LTC3576-1_15 [Linear]

Switching Power Manager with USB On-the-Go Triple Step-Down DC/DCs;
LTC3576-1_15
型号: LTC3576-1_15
厂家: Linear    Linear
描述:

Switching Power Manager with USB On-the-Go Triple Step-Down DC/DCs

文件: 总48页 (文件大小:593K)
中文:  中文翻译
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LTC3576/LTC3576-1  
Switching Power Manager  
with USB On-the-Go + Triple  
Step-Down DC/DCs  
DESCRIPTION  
FEATURES  
Bidirectional Switching Regulator with Bat-Track™ The LTC®3576/LTC3576-1 are highly integrated power  
Adaptive Output Control Provides Efficient Charging management and battery charger ICs for Li-Ion/Polymer  
n
and a 5V Output for USB On-The-Go  
Bat-Track Control of External High Voltage Step-  
Down Switching Regulator  
battery applications. They each include a high efficiency,  
bidirectional switching PowerPath™ manager with auto-  
maticloadprioritization,abatterycharger,anidealdiode,a  
controller for an external high voltage switching regulator  
andthreegeneralpurposestep-downswitchingregulators  
n
n
n
n
Overvoltage Protection Guards Against Damage  
Instant-On Operation with Discharged Battery  
2
2
Triple Step-Down Switching Regulators with I C  
with I C adjustable output voltages. The internal switch-  
Adjustable Outputs (1A/400mA/400mA I  
)
ing regulators automatically limit input current for USB  
compatibility and can also generate 5V at 500mA for USB  
on-the-go applications when powered from the battery.  
BoththeUSBandexternalswitchingregulatorpowerpaths  
featureBat-Trackoptimizedchargingtoprovidemaximum  
180mΩ Internal Ideal Diode + ExternalOIUdTeal Diode  
Controller Powers the Load in Battery Mode  
n
n
n
n
Li-Ion/Polymer Battery Charger (1.5A Max I  
Battery Float Voltage: 4.2V (LTC3576), 4.1V (LTC3576-1)  
)
CHG  
Compact (4mm × 6mm × 0.75mm) 38-Pin QFN Package power to the application from supplies as high as 38V. An  
overvoltage circuit protects the LTC3576/LTC3576-1 from  
damageduetohighvoltageontheV  
orWALLpinswith  
BUS  
APPLICATIONS  
justtwoexternalcomponents.TheLTC3576/LTC3576-1are  
available in a low profile 38-pin (4mm × 6mm × 0.75mm)  
QFN package.  
n
HDD-Based Media Players  
n
GPS, PDAs, Digital Cameras, Smart Phones  
n
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear  
Technology Corporation. Bat-Track and PowerPath are trademarks of Linear Technology  
Corporation. All other trademarks are the property of their respective owners. Protected by U.S.  
Patents, including 6522118, 6404251.  
Automotive Compatible Portable Electronics  
TYPICAL APPLICATION  
High Efficiency PowerPath Manager with Overvoltage Protection  
and Triple Step-Down Regulator  
AUTOMOTIVE  
LT3653  
FIREWIRE, ETC.  
PowerPath Switching Regulator Efficiency  
to System Load (PVOUT/PVBUS  
)
USB OR  
5V AC  
ADAPTER  
OVERVOLTAGE  
PROTECTION  
EXTERNAL HIGH VOLTAGE  
BUCK CONTROLLER  
100  
90  
80  
70  
60  
50  
40  
30  
20  
10  
0
TO OTHER  
LOADS  
USB COMPLIANT  
BIDIRECTIONAL  
SWITCHING  
BAT = 4.2V  
BAT = 3.3V  
REGULATOR  
CC/CV  
0V  
OPTIONAL  
BATTERY  
CHARGER  
CHARGE  
LTC3576/LTC3576-1  
+
Li-Ion  
T
V
I
= 5V  
BUS  
= 0mA  
BAT  
10x MODE  
3.3V/20mA  
RTC/LOW  
ALWAYS ON LDO  
POWER LOGIC  
10  
100  
1000  
0.8V TO 3.6V/400mA  
0.8V TO 3.6V/400mA  
LOAD CURRENT (mA)  
1
2
3
MEMORY  
I/O  
TRIPLE  
HIGH EFFICIENCY  
STEP-DOWN  
SWITCHING  
REGULATORS  
6
3576 TA01b  
ENABLE  
CONTROLS  
0.8V TO 3.6V/1A  
CORE  
μPROCESSOR  
RST  
2
2
2
I C  
I C PORT  
3576 TA01  
3576fb  
1
LTC3576/LTC3576-1  
ABSOLUTE MAXIMUM RATINGS  
PIN CONFIGURATION  
(Notes 1, 2, 3)  
TOP VIEW  
V
, WALL (Transient) t < 1ms,  
BUS  
Duty Cycle < 1% .......................................... –0.3V to 7V  
V
V
, WALL (Static), BAT, V , V , V  
,
38 37 36 35 34 33 32  
BUS  
IN1 IN2 IN3  
CLPROG  
LDO3V3  
NTCBIAS  
NTC  
1
2
3
4
5
6
7
8
9
31 IDGATE  
, ENOTG, NTC, SDA, SCL, DV ,  
OUT  
CC  
30 CHRG  
RST3, CHRG ................................................ –0.3V to 6V  
, I ........ –0.3V to Max(V , V , BAT) + 0.3V  
PROG  
29  
28  
I
LIM0 ILIM1  
BUS OUT  
ACPR  
EN1, EN2, EN3 .............................. –0.3V to V  
+ 0.3V  
OUT  
INx  
OVGATE  
OVSENS  
FB1  
27 WALL  
FBx (x = 1, 2, 3) ..............................–0.3V to V + 0.3V  
V
26  
25 FB2  
24  
C
39  
I
I
I
I
I
I
...................................................................10mA  
OVSENS  
CLPROG  
CHRG RST3  
PROG  
LDO3V3  
SW1 SW2  
I , I  
....................................................................3mA  
V
V
IN1  
IN2  
SW1  
23 SW2  
22 EN2  
21 RST3  
, I  
............................................................50mA  
EN1 10  
........................................................................2mA  
ENOTG 11  
...................................................................30mA  
20  
FB3  
DV  
CC  
12  
, I  
(Continuous).......................................600mA  
13 14 15 16 17 18 19  
UFE PACKAGE  
, I , I  
(Continuous)..............................2A  
SW SW3 BAT VOUT  
Maximum Junction Temperature........................... 125°C  
Operating Temperature Range..................–40°C to 85°C  
Storage Temperature Range...................–65°C to 125°C  
38-LEAD (4mm s 6mm) PLASTIC QFN  
T
JMAX  
= 125°C, θ = 34°C/W  
JA  
EXPOSED PAD (PIN 39) IS GND, MUST BE SOLDERED TO PCB  
ORDER INFORMATION  
LEAD FREE FINISH  
LTC3576EUFE#PBF  
LTC3576EUFE-1#PBF  
TAPE AND REEL  
PART MARKING  
3576  
PACKAGE DESCRIPTION  
TEMPERATURE RANGE  
LTC3576EUFE#TRPBF  
LTC3576EUFE-1#TRPBF  
–40°C to 85°C  
–40°C to 85°C  
38-Lead (4mm × 6mm) Plastic QFN  
38-Lead (4mm × 6mm) Plastic QFN  
35761  
Consult LTC Marketing for parts specified with wider operating temperature ranges.  
Consult LTC Marketing for information on non-standard lead based finish parts.  
For more information on lead free part marking, go to: http://www.linear.com/leadfree/  
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/  
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating  
temperature range, otherwise specifications are at TA = 25°C. VBUS = 5V, BAT = 3.8V, DVCC = 3.3V, RCLPROG = 3.01k, unless  
otherwise noted.  
SYMBOL  
PARAMETER  
CONDITIONS  
MIN  
TYP  
MAX  
UNITS  
PowerPath Switching Regulator—Step-Down Mode  
V
I
Input Supply Voltage  
Total Input Current  
4.35  
5.5  
V
BUS  
l
l
l
l
l
82  
440  
800  
0.32  
1.6  
90  
100  
500  
1000  
0.5  
mA  
mA  
mA  
mA  
mA  
1× Mode  
VBUS(LIM)  
472  
880  
0.39  
2.05  
5× Mode  
10× Mode  
Low Power Suspend Mode  
High Power Suspend Mode  
2.5  
I
(Note 4) Input Quiescent Current  
7
mA  
mA  
mA  
1× Mode  
VBUSQ  
17  
5×, 10× Modes  
0.045  
Low/High Power Suspend Modes  
3576fb  
2
LTC3576/LTC3576-1  
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating  
temperature range, otherwise specifications are at TA = 25°C. VBUS = 5V, BAT = 3.8V, DVCC = 3.3V, RCLPROG = 3.01k, unless  
otherwise noted.  
SYMBOL  
PARAMETER  
CONDITIONS  
MIN  
TYP  
MAX  
UNITS  
h
Ratio of Measured V  
Current to  
210  
1160  
2200  
9.6  
mA/mA  
mA/mA  
mA/mA  
mA/mA  
mA/mA  
1× Mode  
CLPROG  
BUS  
(Note 4)  
CLPROG Program Current  
5× Mode  
10× Mode  
Low Power Suspend Mode  
High Power Suspend Mode  
56  
I
V
Current Available Before  
OUT  
121  
667  
1217  
0.31  
2
mA  
mA  
mA  
mA  
mA  
1× Mode, BAT = 3.3V  
VOUT(POWERPATH)  
Discharging Battery  
5× Mode, BAT = 3.3V  
10× Mode, BAT = 3.3V  
Low Power Suspend Mode  
High Power Suspend Mode  
0.26  
1.6  
0.41  
2.4  
V
V
V
V
CLPROG Servo Voltage in Current Limit  
Switching Modes  
Suspend Modes  
1.18  
100  
V
CLPROG  
UVLO  
mV  
V
Undervoltage Lockout  
Rising Threshold  
Falling Threshold  
4.30  
4.00  
4.35  
V
V
BUS  
BUS  
3.95  
V
to BAT Differential Undervoltage  
Rising Threshold  
Falling Threshold  
200  
50  
mV  
mV  
DUVLO  
OUT  
Lockout  
V
Voltage  
1×, 5×, 10× Modes, 0V < BAT < 4.2V,  
OUT  
3.4  
4.5  
BAT + 0.3  
4.6  
4.7  
4.7  
V
V
I
= 0mA, Battery Charger Off  
VOUT  
USB Suspend Modes, I  
= 250μA  
VOUT  
f
Switching Frequency  
PMOS On-Resistance  
1.8  
2.25  
0.18  
2.7  
MHz  
OSC  
R
PMOS_  
POWERPATH  
R
NMOS On-Resistance  
0.30  
NMOS_  
POWERPATH  
I
Peak Inductor Current Limit  
1
2
3
A
A
A
1× Mode (Note 5)  
5× Mode (Note 5)  
10× Mode (Note 5)  
PEAK_POWERPATH  
R
Suspend LDO Output Resistance  
Closed Loop  
10  
SUSP  
PowerPath Switching Regulator—Step-Up Mode (USB On-the-Go)  
V
BUS  
V
OUT  
Output Voltage  
0mA ≤ I  
≤ 500mA, V > 3.2V  
OUT  
4.75  
2.9  
5.25  
5.5  
V
V
VBUS  
Input Voltage  
l
I
I
I
Output Current Limit  
Peak Inductor Current Limit  
550  
680  
1.8  
mA  
A
VBUS  
PEAK  
OTGQ  
(Note 5)  
V
Quiescent Current  
V
= 3.8V, I = 0mA (Note 6)  
VBUS  
1.38  
1.15  
mA  
V
OUT  
OUT  
BUS  
V
V
Output Current Limit Servo Voltage  
CLPROG  
V
V
UVLO—V  
UVLO—V  
Falling  
Rising  
2.5  
2.6  
2.8  
V
V
OUT(UVLO)  
OUT  
OUT  
OUT  
OUT  
2.9  
t
Short-Circuit Fault Delay  
V
< 4V and PMOS Switch Off  
7.2  
ms  
SCFAULT  
Bat-Track Switching Regulator Control  
V
Absolute WALL Input Threshold  
Rising Threshold  
Hysteresis  
4.2  
0
4.3  
1.1  
4.4  
45  
V
V
WALL  
Differential WALL Input Threshold  
WALL-BAT Falling  
Hysteresis  
30  
60  
mV  
mV  
ΔV  
WALL  
V
Regulation Target Under V Control  
3.55  
BAT + 0.3  
400  
V
μA  
V
OUT  
C
I
WALL Quiescent Current  
ACPR Pull-Down Strength  
ACPR High Voltage  
WALLQ  
R
150  
ACPR  
V
V
V
OUT  
HACPR  
LACPR  
ACPR Low Voltage  
0
V
3576fb  
3
LTC3576/LTC3576-1  
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating  
temperature range, otherwise specifications are at TA = 25°C. VBUS = 5V, BAT = 3.8V, DVCC = 3.3V, RCLPROG = 3.01k, unless  
otherwise noted.  
SYMBOL  
PARAMETER  
CONDITIONS  
MIN  
TYP  
MAX  
UNITS  
Overvoltage Protection  
V
V
Overvoltage Protection Threshold  
OVGATE Output Voltage  
With 6.2k Series Resistor  
6.1  
6.35  
6.7  
12  
V
OVCUTOFF  
OVGATE  
V
V
< V  
> V  
1.88•V  
V
V
OVSENS  
OVSENS  
OVCUTOFF  
OVCUTOFF  
OVSENS  
0
t
OVGATE Time to Reach Regulation  
BAT Regulated Output Voltage  
OVGATE C  
= 1nF  
LOAD  
2.2  
ms  
RISE  
Battery Charger  
V
LTC3576  
4.179  
4.165  
4.200  
4.200  
4.221  
4.235  
V
V
FLOAT  
l
l
LTC3576-1  
4.079  
4.065  
4.100  
4.100  
4.121  
4.135  
V
V
I
I
Constant Current Mode Charger Current  
Battery Drain Current  
R
R
= 1k  
= 5k  
980  
185  
1030  
206  
1065  
223  
mA  
mA  
CHG  
BAT  
PROG  
PROG  
V
VOUT  
> V  
, Suspend Mode,  
UVLO  
3.6  
6
μA  
BUS  
I
= 0μA  
= 0V, I  
V
= 0μA  
VOUT  
28  
45  
μA  
BUS  
(Ideal Diode Mode)  
V
V
V
PROG Pin Servo Voltage  
1.000  
0.100  
100  
1030  
100  
2.85  
135  
–100  
4
V
V
PROG  
PROG_TRKL  
C/10  
PROG Pin Servo Voltage in Trickle Charge BAT < V  
C/10 Threshold Voltage at PROG  
TRKL  
mV  
h
Ratio of I to PROG Pin Current  
mA/mA  
mA  
PROG  
BAT  
I
Trickle Charge Current  
BAT < V  
, R  
= 1k  
TRKL  
TRKL PROG  
V
TRKL  
Trickle Charge Threshold Voltage  
Trickle Charge Hysteresis Voltage  
Recharge Battery Threshold Voltage  
Safety Timer Termination Period  
Bad Battery Termination Time  
End of Charge Current Ratio  
CHRG Pin Output Low Voltage  
CHRG Pin Leakage Current  
BAT Rising  
2.7  
3.0  
V
mV  
ΔV  
ΔV  
TRKL  
Threshold Voltage Relative to V  
–75  
3.3  
–125  
5
mV  
FLOAT  
RECHRG  
t
t
Timer Starts When V = V  
Hour  
Hour  
mA/mA  
mV  
TERM  
BADBAT  
BAT  
FLOAT  
BAT < V  
0.4  
0.5  
0.6  
0.112  
100  
1
TRKL  
h
(Note 7)  
0.085  
0.1  
C/10  
V
I
= 5mA  
= 5V  
65  
CHRG  
CHRG  
CHRG  
I
V
μA  
CHRG  
R
Battery Charger Power FET On-  
0.18  
110  
ON_CHG  
Resistance (Between V  
and BAT)  
OUT  
T
LIM  
Junction Temperature in Constant  
Temperature Mode  
°C  
NTC  
V
Cold Temperature Fault Threshold Voltage Rising Threshold  
Hysteresis  
75  
76.5  
1.6  
78  
%NTCBIAS  
%NTCBIAS  
COLD  
V
V
Hot Temperature Fault Threshold Voltage Falling Threshold  
Hysteresis  
33.4  
0.7  
34.9  
1.5  
36.4  
2.7  
50  
%NTCBIAS  
%NTCBIAS  
HOT  
NTC Disable Threshold Voltage  
Falling Threshold  
Hysteresis  
1.7  
50  
%NTCBIAS  
mV  
DIS  
I
NTC Leakage Current  
NTC = NTCBIAS = 5V  
–50  
nA  
NTC  
Ideal Diode  
V
Forward Voltage  
I
I
= 10mA  
15  
mV  
FWD  
VOUT  
R
Internal Diode On-Resistance Dropout  
Diode Current Limit  
= 200mA  
0.18  
DROPOUT  
VOUT  
I
2
A
MAX_DIODE  
3576fb  
4
LTC3576/LTC3576-1  
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating  
temperature range, otherwise specifications are at TA = 25°C. VBUS = 5V, BAT = 3.8V, DVCC = 3.3V, RCLPROG = 3.01k, unless  
otherwise noted.  
SYMBOL  
PARAMETER  
CONDITIONS  
MIN  
TYP  
MAX  
UNITS  
Always On 3.3V LDO Supply  
V
Regulated Output Voltage  
0mA < I < 20mA  
LDO3V3  
3.1  
3.3  
2.7  
23  
3.5  
V
LDO3V3  
R
R
Closed-Loop Output Resistance  
Dropout Output Resistance  
CL_LDO3V3  
OL_LDO3V3  
Logic (I  
, I  
, EN1, EN2, EN3, ENOTG, and SCL, SDA when DV = 0V)  
LIM0 LIM1  
CC  
V
V
Logic Low Input Voltage  
Logic High Input Voltage  
0.4  
5.5  
V
V
IL  
IH  
1.2  
1.6  
I
I
, I , EN1, EN2, EN3, ENOTG, SCL,  
LIM0 LIM1  
2
μA  
PD1  
SDA Pull-Down Current  
2
I C Port  
DV  
Input Supply  
V
μA  
V
CC  
I
DV Current  
CC  
SCL/SDA = 0kHz, DV = 3.3V  
0.5  
1.0  
DVCC  
CC  
V
DV UVLO  
CC  
DVCC(UVLO)  
2
ADDRESS  
V , SDA, SCL  
I C Address  
0001001[0]  
Input High Threshold  
Input Low Threshold  
Pull-Down Current  
70  
%DV  
%DV  
IH  
CC  
CC  
V , SDA, SCL  
IL  
30  
I
, SDA, SCL  
PD2  
2
μA  
V
V
Digital Output Low (SDA)  
Clock Operating Frequency  
I
= 3mA  
0.4  
OL  
SCL  
BUF  
SDA  
f
t
400  
kHz  
μs  
Bus Free Time Between Stop and Start  
Condition  
1.3  
0.6  
t
Hold Time After (Repeated) Start  
Condition  
μs  
HD_STA  
t
t
t
t
t
t
t
t
t
t
Repeated Start Condition Setup Time  
Stop Condition Setup Time  
Data Hold Time Output  
Data Hold Time Input  
Data Setup Time  
0.6  
0.6  
0
μs  
μs  
ns  
ns  
ns  
μs  
μs  
ns  
ns  
ns  
SU_STA  
SU_STO  
HD_DAT(O)  
HD_DAT(I)  
SU_DAT  
LOW  
900  
0
100  
1.3  
0.6  
20  
20  
SCL Low Period  
SCL High Period  
HIGH  
SDA/SCL Fall Time  
300  
300  
50  
f
SDA/SCL Rise Time  
r
Input Spike Suppression Pulse Width  
SP  
General Purpose Switching Regulators 1, 2 and 3  
V
V
Input Supply Voltage  
(Note 8)  
Connected to V Through  
OUT  
2.7  
2.5  
5.5  
2.9  
V
IN1,2,3  
V
V
UVLO—V  
UVLO—V  
Falling  
Rising  
V
2.6  
2.8  
V
V
OUT(UVLO)  
OUT  
OUT  
OUT  
OUT  
IN1,2,3  
Low Impedance. Switching  
Regulators are Disabled in UVLO  
f
I
Switching Frequency  
FBx Input Current  
1.8  
–50  
100  
2.25  
2.7  
50  
MHz  
nA  
OSC  
V
= 0.85V  
FB1,2,3  
FB1,2,3  
D1,2,3  
Maximum Duty Cycle  
SWx Pull-Down in Shutdown  
%
R
10  
kꢀ  
SW1,2,3_PD  
3576fb  
5
LTC3576/LTC3576-1  
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating  
temperature range, otherwise specifications are at TA = 25°C. VBUS = 5V, BAT = 3.8V, DVCC = 3.3V, RCLPROG = 3.01k, unless  
otherwise noted.  
SYMBOL  
PARAMETER  
CONDITIONS  
MIN  
TYP  
90  
MAX  
UNITS  
μA  
μA  
μA  
μA  
V
I
Pulse-Skipping Mode Input Current  
Burst Mode® Input Current  
LDO Mode Input Current  
Shutdown Input Current Limit  
Maximum Servo Voltage  
Minimum Servo Voltage  
I
I
I
I
= 0μA (Note 9)  
= 0μA (Note 9)  
= 0μA (Note 9)  
= 0μA, FB1,2,3 = 0V  
VIN1,2,3  
OUT1,2,3  
OUT1,2,3  
OUT1,2,3  
OUT1,2,3  
20  
35  
25  
15  
1
l
V
V
V
Full Scale (1,1,1,1) (Note 10)  
Zero Scale (0,0,0,0) (Note 10)  
0.78  
0.80  
0.425  
25  
0.82  
0.445  
FBHIGH1,2,3  
FBLOW1,2,3  
LSB1,2,3  
0.405  
V
V
Servo Voltage Step Size  
mV  
FB1,2  
R
R
LDO Mode Closed-Loop R  
V
= V = 0.8V  
OUT1,2 3  
0.25  
2.5  
LDO_CL1,2,3  
OUT  
FB1,2,3  
LDO Mode Open-Loop R  
(Note 11)  
LDO_OL1,2,3  
OUT  
General Purpose Switching Regulator 1 and 2  
I
PMOS Switch Current Limit  
Pulse-Skipping/Burst Mode  
Operation (Note 5)  
600  
50  
900  
1300  
2800  
mA  
LIM1,2  
I
Available Output Current  
LDO Mode  
mA  
OUT1,2  
R
R
PMOS R  
NMOS R  
0.6  
0.7  
P1,2  
DS(ON)  
N1,2  
DS(ON)  
General Purpose Switching Regulator 3  
I
PMOS Switch Current Limit  
Pulse-Skipping/Burst Mode  
Operation (Note 5)  
1300  
50  
1800  
mA  
LIM3  
I
Available Output Current  
LDO Mode  
mA  
OUT3  
R
R
PMOS R  
NMOS R  
0.18  
0.3  
P3  
DS(0N)  
N3  
DS(ON)  
t
Power-On Reset Time for Switching  
Regulator  
V
Within 92% of Final Value to  
230  
ms  
RST3  
FB3  
RST3 Hi-Z  
Burst Mode is a registered trademark of Linear Technology Corporation.  
Note 1: Stresses beyond those listed under Absolute Maximum Ratings  
may cause permanent damage to the device. Exposure to any Absolute  
Maximum Rating condition for extended periods may affect device  
reliability and lifetime.  
Note 5: The current limit features of this part are intended to protect the  
IC from short term or intermittent fault conditions. Continuous operation  
above the maximum specified pin current rating may result in device  
degradation or failure.  
Note 2: The LTC3576E/LTC3576E-1 are guaranteed to meet performance  
specifications from 0°C to 85°C. Specifications over the –40°C to 85°C  
operating temperature range are assured by design, characterization and  
correlation with statistical process controls.  
Note 6: The bidirectional switcher’s supply current is bootstrapped to V  
BUS  
and in the application will reflect back to V  
by (V /V ) •  
BUS OUT  
OUT  
1/efficiency. Total quiescent current is the sum of the current into the  
pin plus the reflected current.  
V
OUT  
Note 3: The LTC3576E/LTC3576E-1 include overtemperature protection  
that is intended to protect the device during momentary overload  
conditions. Junction temperature will exceed 125°C when overtemperature  
protection is active. Continuous operation above the specified maximum  
operating junction temperature may impair device reliability.  
Note 7: h  
current with indicated PROG resistor.  
Note 8: V not in UVLO.  
Note 9: FBx above regulation such that regulator is in sleep. Specification  
does not include resistive divider current reflected back to V  
Note 10: Applies to pulse-skipping and Burst Mode operation only.  
Note 11: Inductor series resistance adds to open-loop R  
is expressed as a fraction of the measured full charge  
C/10  
OUT  
.
INx  
Note 4: Total input current is the sum of quiescent current, I  
, and  
VBUSQ  
measured current given by V /R  
CLPROG  
• (h  
+ 1).  
CLPROG  
CLPROG  
.
OUT  
3576fb  
6
LTC3576/LTC3576-1  
T = 25°C unless otherwise specified.  
A
TYPICAL PERFORMANCE CHARACTERISTICS  
Ideal Diode Resistance  
VOUT Voltage vs Load Current  
Ideal Diode V-I Characteristics  
vs Battery Voltage  
(Battery Charger Disabled)  
1.0  
0.8  
0.6  
0.4  
0.2  
0
0.25  
0.20  
0.15  
0.10  
0.05  
0
4.50  
INTERNAL IDEAL DIODE  
WITH SUPPLEMENTAL  
EXTERNAL VISHAY  
Si2333 PMOS  
BAT = 4V  
4.25  
4.00  
INTERNAL IDEAL  
DIODE  
INTERNAL IDEAL  
DIODE ONLY  
BAT = 3.4V  
3.75  
INTERNAL IDEAL DIODE  
WITH SUPPLEMENTAL  
EXTERNAL VISHAY  
Si2333 PMOS  
3.50  
3.25  
V
= 5V  
BUS  
0
0.04  
0.08  
0.12  
0.16  
0.20  
2.7  
3.0  
3.3  
3.6  
3.9  
4.2  
0
0.1 0.2 0.3  
0.6 0.7 0.8 0.9 1.0  
0.4 0.5  
FORWARD VOLTAGE (V)  
BATTERY VOLTAGE (V)  
LOAD CURRENT (A)  
3576 G01  
3576 G02  
3576 G03  
USB Limited Load Current vs Battery  
Voltage (Battery Charger Disabled)  
Battery and VBUS Currents  
vs Load Current  
Battery Charge Current  
vs Temperature  
750  
500  
250  
900  
600  
500  
400  
300  
200  
100  
0
R = 2k  
PROG  
V
= 5V  
BUS  
800  
700  
600  
500  
400  
300  
200  
100  
5s MODE  
V
CURRENT  
BUS  
THERMAL REGULATION  
BATTERY CURRENT  
(CHARGING)  
0
–250  
–500  
V
= 5V  
BUS  
BAT = 3.8V  
5s MODE  
R
R
= 3.01k  
BATTERY CURRENT  
(DISCHARGING)  
CLPROG  
= 1k  
PROG  
0
60 80  
TEMPERATURE (°C)  
–40 –20  
0
20 40  
100 120  
0
100 200 300 400 500 600 700 800 9001000  
2.7  
3.9  
4.2  
3.0  
3.3  
3.6  
LOAD CURRENT (mA)  
BATTERY VOLTAGE (V)  
3576 G06  
3576 G05  
3576 G04  
Battery Charging Efficiency  
vs Battery Voltage with No  
PowerPath Switching Regulator  
Transient Response  
PowerPath Switching Regulator  
Efficiency vs Load Current  
External Load (PBAT/PVBUS  
)
100  
90  
80  
70  
60  
50  
40  
30  
95  
90  
85  
80  
75  
70  
65  
60  
55  
R
R
= 3.01k  
CLPROG  
PROG  
= 1k  
V
OUT  
50mV/DIV  
1s MODE  
1s MODE  
AC COUPLED  
5s, 10s MODE  
I
VOUT  
500mA/DIV  
0mA  
5s MODE  
3576 G07  
V
V
= 5V  
20μs/DIV  
BUS  
OUT  
= 3.65V  
CHARGER OFF  
50  
10s MODE  
10  
1000  
100  
2.7  
3.9  
4.2  
3.0  
3.3  
3.6  
LOAD CURRENT (mA)  
BATTERY VOLTAGE (V)  
3576 G08  
3576 G09  
3576fb  
7
LTC3576/LTC3576-1  
T = 25°C unless otherwise specified.  
A
TYPICAL PERFORMANCE CHARACTERISTICS  
VBUS Quiescent Current  
vs VBUS Voltage (Suspend)  
VOUT Voltage  
vs Load Current in Suspend  
VBUS Current  
vs Load Current in Suspend  
60  
50  
5.0  
4.5  
4.0  
3.5  
3.0  
2.5  
2.5  
2.0  
1.5  
1.0  
0.5  
0
V
= 5V  
BUS  
BAT = 3.3V  
= 3.01k  
HIGH POWER SUSPEND  
R
CLPROG  
40  
30  
HIGH POWER  
SUSPEND  
LOW POWER SUSPEND  
20  
10  
0
LOW POWER SUSPEND  
V
= 5V  
BAT = 3.3V  
BUS  
R
= 3.01k  
CLPROG  
0
1
2
3
4
5
0
0.5  
1.0  
1.5  
2.0  
2.5  
0
0.5  
1.0  
1.5  
2.0  
2.5  
BUS VOLTAGE (V)  
LOAD CURRENT (mA)  
LOAD CURRENT (mA)  
3576 G10  
3576 G11  
3576 G12  
Battery Charge Current  
vs VOUT Voltage  
V
OUT Voltage vs Battery Voltage  
Normalized Battery Charger Float  
Voltage vs Temperature  
(Charger Overprogrammed)  
1.001  
1.000  
0.999  
0.998  
0.997  
0.996  
600  
500  
400  
300  
200  
100  
0
4.7  
4.5  
4.3  
4.1  
3.9  
3.7  
3.5  
3.3  
3.1  
2.9  
2.7  
R
R
= 3.01k  
V
I
R
R
= 5V  
= 0V  
CLPROG  
PROG  
5s MODE  
BUS  
VOUT  
= 2k  
= 3.01k  
CLPROG  
PROG  
= 1k  
5s MODE  
1s MODE  
3.65 3.70  
3.40 3.45 3.50 3.55 3.60  
3.75 3.80  
–40  
–15  
10  
35  
60  
85  
2.7  
3.0  
3.3  
3.6  
3.9  
4.2  
V
(V)  
OUT  
TEMPERATURE (°C)  
BATTERY VOLTAGE (V)  
3576 G13  
3576 G15  
3576 G14  
VBUS Quiescent Current  
vs Temperature  
VBUS Quiescent Current in  
Suspend vs Temperature  
Battery Drain Current  
vs Temperature  
60  
50  
35  
30  
25  
20  
15  
10  
5
25  
20  
15  
10  
5
V = 5V  
BUS  
V
= 5V  
BUS  
5s MODE  
40  
30  
20  
10  
0
1s MODE  
BAT = 3.8V  
= 0V  
V
BUS  
SWITCHING  
REGULATORS OFF  
0
0
–40  
–15  
10  
35  
60  
85  
–40  
–15  
10  
35  
60  
TEMPERATURE (°C)  
85  
–40  
–15  
10  
35  
60  
85  
TEMPERATURE (°C)  
TEMPERATURE (°C)  
3576 G17  
3576 G18  
3576 G16  
3576fb  
8
LTC3576/LTC3576-1  
T = 25°C unless otherwise specified.  
A
TYPICAL PERFORMANCE CHARACTERISTICS  
OTG Boost Quiescent Current  
vs VOUT Voltage  
OTG Boost Efficiency  
vs Load Current  
100  
OTG Boost VBUS Voltage  
vs Load Current  
5.5  
5.0  
4.5  
4.0  
3.5  
3.0  
2.5  
2.3  
2.1  
1.9  
1.7  
1.5  
1.3  
1.1  
0.9  
0.7  
0.5  
90  
80  
70  
60  
V
= 4.75V  
BUS  
I
= 500mA  
VBUS  
V
V
V
V
= 5V  
V
V
V
V
= 5V  
OUT  
OUT  
OUT  
OUT  
OUT  
OUT  
OUT  
OUT  
= 4.4V  
= 3.8V  
= 3.2V  
= 4.4V  
= 3.8V  
= 3.2V  
50  
40  
2.90  
3.55  
4.20  
(V)  
4.85  
5.50  
0
100 200 300 400 500 600 700  
LOAD CURRENT (mA)  
1
10  
LOAD CURRENT (mA)  
100  
1000  
V
OUT  
3576 G20  
3576 G19  
3576 G21  
OTG Boost Start-Up Time into  
Current Source Load  
vs VOUT Voltage  
OTG Boost Efficiency  
vs VOUT Voltage  
OTG Boost Burst Mode Current  
Threshold vs VOUT Voltage  
400  
300  
200  
100  
0
2.50  
2.25  
2.00  
1.75  
95  
90  
85  
80  
75  
70  
500mA LOAD  
100mA LOAD  
22μF ON V , 22μF AND  
BUS  
LOAD THROUGH OVP  
RISING THRESHOLD  
FALLING THRESHOLD  
22μF ON V  
,
BUS  
NO OVP  
22μF ON V  
,
BUS  
LOAD THROUGH OVP  
1.50  
4.20  
(V)  
4.85  
2.90  
5.50  
3.55  
2.9  
3.4  
3.9  
V
4.4  
(V)  
4.9  
5.4  
3.55  
4.20  
(V)  
4.85  
2.90  
5.50  
V
OUT  
V
OUT  
OUT  
3576 G24  
3576 G23  
3576 G22  
OTG Boost Start-Up into Current  
Source Load  
OTG Boost Transient Response  
OTG Boost Burst Mode Operation  
V
BUS  
50mV/DIV  
V
AC COUPLED  
BUS  
50mV/DIV  
I
VBUS  
AC COUPLED  
200mA/DIV  
V
SW  
1V/DIV  
0mA  
I
VBUS  
V
200mA/DIV  
BUS  
2V/DIV  
0V  
0mA  
0V  
3576 G26  
3576 G27  
3576 G25  
V
I
= 3.8V  
= 500mA  
200μs/DIV  
V
I
= 3.8V  
= 10mA  
50μs/DIV  
V
= 3.8V  
20μs/DIV  
OUT  
LOAD  
OUT  
LOAD  
OUT  
3576fb  
9
LTC3576/LTC3576-1  
T = 25°C unless otherwise specified.  
A
TYPICAL PERFORMANCE CHARACTERISTICS  
Battery Charging from USB-HV  
BUCK-USB  
Oscillator Frequency  
vs Temperature  
USB OTG from BAT-HV BUCK-BAT  
2.30  
2.25  
2.20  
2.15  
V
V
OUT  
OUT  
1V/DIV  
1V/DIV  
AC COUPLED  
AC COUPLED  
V
V
BUS  
BUS  
100mV/DIV  
200mV/DIV  
AC COUPLED  
AC COUPLED  
V
SW  
I
BAT  
1A/DIV  
5V/DIV  
0V  
0A  
HVOK  
5V/DIV  
HVOK  
5V/DIV  
0V  
V
V
V
V
V
= 5V  
OUT  
OUT  
OUT  
OUT  
OUT  
= 4.2V  
= 3.6V  
= 3V  
0V  
2.10  
3576 G28  
3576 G29  
V
= 5V  
500μs/DIV  
V
I
= 3.8V  
500μs/DIV  
BUS  
BAT  
BUS  
HV = 12V  
IN  
= 285mA  
= 2.7V  
USING LT3653  
HV = 12V  
IN  
2.05  
USING LT3653  
–40  
–15  
10  
35  
60  
85  
TEMPERATURE (°C)  
3576 G30  
Rising OVP Threshold  
vs Temperature  
OVP Connect Waveform  
OVP Disconnect Waveform  
6.280  
6.275  
6.270  
6.265  
6.260  
6.255  
V
BUS  
V
BUS  
5V/DIV  
5V/DIV  
OVGATE  
5V/DIV  
OVGATE  
5V/DIV  
OVP INPUT  
VOLTAGE  
5V TO 10V  
STEP 5V/DIV  
OVP INPUT  
VOLTAGE  
0V TO 5V  
STEP 5V/DIV  
3576 G32  
3576 G31  
500μs/DIV  
500μs/DIV  
–40  
–15  
10  
35  
60  
85  
TEMPERATURE (°C)  
3576 G33  
OVGATE Quiescent Current  
vs Temperature  
RST3, CHRG Pin Current  
vs Voltage (Pull-Down State)  
OVGATE vs OVSENS  
12  
10  
37  
35  
33  
31  
29  
27  
100  
80  
60  
40  
20  
0
V
= 5V  
OVSENS CONNECTED  
TO INPUT THROUGH  
6.2k RESISTOR  
V
= 5V  
BUS  
OVSENS  
BAT = 3.8V  
8
6
4
2
0
–15  
10  
35  
60  
85  
0
1
2
3
4
5
0
2
4
6
8
–40  
INPUT VOLTAGE (V)  
TEMPERATURE (°C)  
RST3, CHRG PIN VOLTAGE (V)  
3576 G34  
3576 G35  
3576 G36  
3576fb  
10  
LTC3576/LTC3576-1  
T = 25°C unless otherwise specified.  
A
TYPICAL PERFORMANCE CHARACTERISTICS  
3.3V LDO Output Voltage  
vs Load Current, VBUS = 0V  
3.3V LDO Step Response  
(5mA to 15mA)  
Battery Drain Current  
vs Battery Voltage  
35  
3.4  
3.2  
3.0  
2.8  
2.6  
I
= 0mA  
BAT = 3.4V  
VOUT  
BAT = 3.9V, 4.2V  
BAT = 3.5V  
BAT = 3.6V  
30  
I
LDO3V3  
V
= 0V  
BUS  
5mA/DIV  
25  
20  
15  
10  
5
0mA  
V
LDO3V3  
20mV/DIV  
AC COUPLED  
BAT = 3V  
V
= 5V  
BUS  
BAT = 3.1V  
BAT = 3.2V  
BAT = 3.3V  
3576 G38  
(SUSPEND MODE)  
BAT = 3.8V  
20μs/DIV  
0
2.7  
3.0  
3.3  
3.6  
4.2  
3.9  
0
5
10  
15  
20  
25  
BATTERY VOLTAGE (V)  
LOAD CURRENT (mA)  
3576 G39  
3576 G37  
Switching Regulator Soft-Start  
Waveform  
Switching Regulator Current Limit  
vs Temperature  
RDS(ON) for Switching Regulator  
Power Switches vs Temperature  
2.0  
1.5  
1.0  
0.5  
0
1.0  
0.8  
0.6  
0.4  
0.2  
0
REGULATOR 3  
REGULATORS 1, 2  
NMOS SWITCH  
PMOS SWITCH  
REGULATOR 3  
REGULATORS 1, 2  
NMOS SWITCH  
PMOS SWITCH  
3576 G40  
50μs/DIV  
V
= 3.8V  
IN1,2,3  
–40  
–15  
10  
35  
60  
85  
–40  
–15  
10  
35  
60  
85  
TEMPERATURE (°C)  
TEMPERATURE (°C)  
3576 G42  
3576 G41  
Switching Regulators 1, 2  
Pulse-Skipping Mode Efficiency  
Switching Regulators 1, 2  
Burst Mode Efficiency  
Switching Regulator Low Power  
Quiescent Currents vs Temperature  
100  
90  
80  
70  
60  
50  
40  
30  
20  
10  
0
100  
90  
80  
70  
60  
50  
40  
30  
20  
10  
0
100  
90  
80  
70  
60  
50  
40  
30  
20  
10  
0
V
= 2.5V  
V
= 3.8V  
V
= 3.8V  
OUT1,2  
IN3  
IN3  
V
= 2.5V  
OUT1,2  
PULSE-SKIPPING MODE  
V
= 1.2V  
OUT1,2  
V
= 1.2V  
OUT1,2  
= 1.8V  
V
= 1.8V  
OUT1,2  
V
OUT1,2  
Burst Mode OPERATION  
LDO MODE  
0.1  
1
10  
100  
1000  
0.1  
1
10  
100  
1000  
–40  
–15  
10  
35  
60  
85  
LOAD CURRENT (mA)  
LOAD CURRENT (mA)  
TEMPERATURE (°C)  
3576 G44  
3576 G45  
3576 G43  
3576fb  
11  
LTC3576/LTC3576-1  
T = 25°C unless otherwise specified.  
A
TYPICAL PERFORMANCE CHARACTERISTICS  
Switching Regulator Constant  
Frequency Quiescent Currents  
Switching Regulator 3  
Pulse-Skipping Mode Efficiency  
Switching Regulator 3  
Burst Mode Efficiency  
100  
90  
80  
70  
60  
50  
40  
30  
20  
10  
0
100  
90  
80  
70  
60  
50  
40  
30  
20  
10  
0
8
7
6
5
V
= 3.8V  
V
= 2.5V  
OUT3  
V
= 3.8V  
IN3  
IN3  
SWITCHING  
REGULATOR 3  
V
= 2.5V  
OUT3  
V
= 1.2V  
OUT3  
V
= 1.8V  
OUT3  
V
= 1.8V  
OUT3  
V
= 1.2V  
OUT3  
4
3
SWITCHING  
REGULATORS 1, 2  
2
1
0
–15  
10  
TEMPERATURE (°C)  
60  
0.1  
1
10  
100  
1000  
–40  
85  
35  
0.1  
1
10  
100  
1000  
LOAD CURRENT (mA)  
LOAD CURRENT (mA)  
3576 G48  
3576 G47  
3576 G46  
Switching Regulator Mode  
Transition, Pulse-Skipping-LDO-  
Pulse-Skipping  
Switching Regulators 1, 2  
Feedback Voltage vs Load Current  
Switching Regulators 1, 2  
Transient Response  
0.820  
V
Burst Mode  
OPERATION  
OUT3  
V
0.815  
0.810  
OUT2  
50mV/DIV  
50mV/DIV  
AC COUPLED  
AC COUPLED  
PULSE-SKIPPING MODE  
0.805  
0.800  
I
OUT2  
V
SW3  
200mA/DIV  
1V/DIV  
0V  
0mA  
3576 G50  
3576 G51  
0.795  
0.790  
V
V
= 3.8V  
50μs/DIV  
IN2  
OUT2  
V
V
= 3.8V  
50μs/DIV  
IN3  
= 3.4V  
= 1.8V  
OUT3  
OUT3  
I
= 50mA  
0.1  
1
10  
100  
1000  
LOAD CURRENT (mA)  
3576 G49  
Switching Regulator Mode  
Transition, Pulse-Skipping–Burst  
Mode Operation–Pulse-Skipping  
Switching Regulator 3 Feedback  
Voltage vs Load Current  
Switching Regulator 3  
Transient Response  
0.810  
0.805  
0.800  
V
OUT3  
V
OUT3  
50mV/DIV  
AC COUPLED  
50mV/DIV  
Burst Mode  
OPERATION  
AC COUPLED  
I
OUT3  
V
500mA/DIV  
SW3  
1V/DIV  
0V  
PULSE-SKIPPING MODE  
0mA  
0.795  
0.790  
3576 G54  
3576 G53  
V
V
= 3.8V  
50μs/DIV  
V
V
= 3.8V  
50μs/DIV  
IN3  
IN3  
OUT3  
= 1.8V  
= 1.8V  
OUT3  
OUT3  
I
= 100mA  
0.1  
1
10  
100  
1000  
LOAD CURRENT (mA)  
3576 G52  
3576fb  
12  
LTC3576/LTC3576-1  
PIN FUNCTIONS  
CLPROG (Pin 1): USB Current Limit Program and Monitor  
Pin. A 1% resistor from CLPROG to ground determines  
the upper limit of the current drawn or sourced from the  
be connected to V  
and the drain should be connected  
BUS  
to the product’s DC input connector. In the absence of an  
overvoltage condition, this pin is connected to an internal  
chargepumpcapableofcreatingsufficientoverdrivetofully  
enhance the pass transistor. If an overvoltage condition is  
detected, OVGATE is brought rapidly to GND to prevent  
damage to the LTC3576/LTC3576-1. OVGATE works in  
conjunction with OVSENS to provide this protection.  
V
pins. A precise fraction, h  
, of the V  
CLPROG  
cur-  
BUS  
BUS  
rent is sent to the CLPROG pin when the PMOS switch of  
the PowerPath switching regulator is on. The switching  
regulator delivers power until the CLPROG pin reaches  
1.18V in step-down mode and 1.15V in step-up mode.  
When the switching regulator is in step-down mode,  
CLPROG is used to regulate the average input current.  
OVSENS (Pin 6): Overvoltage Protection Sense Input.  
OVSENS should be connected through a 6.2k resistor to  
the input power connector and the drain of an external  
N-channel MOS pass transistor. When the voltage on this  
Several V  
current limit settings are available via user  
BUS  
input which will typically correspond to the 500mA and  
100mA USB specifications. When the switching regulator  
is in step-up mode (USB on-the-go), CLPROG is used to  
limit the average output current to 680mA. A multilayer  
ceramic averaging capacitor or R-C network is required  
at CLPROG for filtering.  
pin exceeds  
V
, the OVGATE pin will be pulled  
OVCUTOFF  
to GND to disable the pass transistor and protect the  
LTC3576/LTC3576-1. The OVSENS pin shunts current  
during an overvoltage transient in order to keep the pin  
voltage at 6V.  
LDO3V3 (Pin 2): 3.3V LDO Output Pin. This pin provides  
FB1 (Pin 7): Feedback Input for Switching Regulator 1.  
Whenregulator1scontrolloopiscomplete,thispinservos  
to 1 of 16 possible set points based on the commanded  
a regulated always-on 3.3V supply voltage. LDO3V3  
gets its power from V . It may be used for light loads  
OUT  
such as a watchdog microprocessor or real time clock.  
A 1μF capacitor is required from LDO3V3 to ground. If  
the LDO3V3 output is not used it should be disabled by  
2
value from the I C serial port. See Table 4.  
V
(Pin 8): Power Input for Switching Regulator 1.  
IN1  
This pin will generally be connected to V . A 1μF MLCC  
connecting it to V  
.
OUT  
OUT  
capacitor is recommended on this pin.  
NTCBIAS (Pin 3): NTC Thermistor Bias Output. If NTC  
operation is desired, connect a bias resistor between  
NTCBIAS and NTC, and an NTC thermistor between NTC  
and GND. To disable NTC operation, connect NTC to GND  
and leave NTCBIAS open.  
SW1 (Pin 9): Power Transmission Pin for Switching  
Regulator 1.  
EN1 (Pin 10): Logic Input. This logic input pin indepen-  
dently enables switching regulator 1. Active high. This  
pin is logically ORed with its corresponding bit in the  
NTC (Pin 4): Input to the Thermistor Monitoring Circuits.  
TheNTCpinconnectstoanegativetemperaturecoefficient  
thermistor,whichistypicallyco-packagedwiththebattery,  
to determine if the battery is too hot or too cold to charge.  
If the battery’s temperature is out of range, charging is  
paused until it re-enters the valid range. A low drift bias  
resistorisrequiredfromNTCBIAStoNTCandathermistor  
is required from NTC to ground. To disable NTC operation,  
connect NTC to GND and leave NTCBIAS open.  
2
I C serial port. See Table 3. Has a 2μA internal pull-down  
current source.  
ENOTG (Pin 11): Logic Input. This logic input pin inde-  
pendently enables the bidirectional switching regulator to  
step up the voltage on V  
and provide a 5V output on  
OUT  
V
for USB on-the-go applications. Active high. This  
BUS  
pin is logically ORed with its corresponding bit in the  
2
I C serial port. See Table 3. Has a 2μA internal pull-down  
current source.  
OVGATE (Pin 5): Overvoltage Protection Gate Output.  
Connect OVGATE to the gate pin of an external N-channel  
MOS pass transistor. The source of the transistor should  
3576fb  
13  
LTC3576/LTC3576-1  
PIN FUNCTIONS  
2
DV (Pin 12): Logic Supply for the I C Serial Port. If the  
RST3 (Pin 21): Logic Output. This in an open-drain output  
which indicates that switching regulator 3 has settled to  
its final value. It can be used as a power-on reset for the  
primary microprocessor or to enable the other switching  
regulators for supply sequencing.  
CC  
serial port is not needed, it can be disabled by grounding  
2
DV . When DV is grounded, the I C bits are set to their  
CC  
CC  
default values. See Table 3.  
2
SCL (Pin 13): Clock Input Pin for the I C Serial Port. The  
2
I C logic levels are scaled with respect to DV . If DV  
EN2 (Pin 22): Logic Input. This logic input pin indepen-  
dently enables switching regulator 2. Active high. This  
pin is logically ORed with its corresponding bit in the  
CC  
CC  
is grounded, the SCL pin is equivalent to the C2, C4 and  
2
C6 bits in the I C serial port. SCL in conjunction with SDA  
2
determine the operating modes of switching regulators 1,  
I C serial port. See Table 3. Has a 2μA internal pull-down  
2 and 3 when DV is grounded. See Tables 3 and 5. Has  
current source.  
CC  
a 2μA internal pull-down current source.  
SW2 (Pin 23): Power Transmission Pin for Switching  
Regulator 2.  
2
SDA (Pin 14): Data Input Pin for the I C Serial Port. The  
2
I C logic levels are scaled with respect to DV . If DV  
CC  
CC  
V
(Pin 24): Power Input for Switching Regulator 2.  
IN2  
is grounded, the SDA pin is equivalent to the C3, C5 and  
This pin will generally be connected to V . A 1μF MLCC  
OUT  
2
C7 bits in the I C serial port. SDA in conjunction with SCL  
capacitor is recommended on this pin.  
determine the operating modes of switching regulators 1,  
FB2 (Pin 25): Feedback Input for Switching Regulator 2.  
Whenregulator2scontrolloopiscomplete,thispinservos  
to 1 of 16 possible set points based on the commanded  
2 and 3 when DV is grounded. See Tables 3 and 5. Has  
CC  
a 2μA internal pull-down current source.  
NC (Pin 15): Unconnected Pin. This pin is not connected  
2
value from the I C serial port. See Table 4.  
internally to the part. It is permissible to tie this pin to V  
IN3  
V (Pin 26): Bat-Track External Switching Regulator  
in order to make the V PCB trace wider.  
C
IN3  
Control Output. This pin drives the V pin of an external  
C
V
IN3  
(Pin 16): Power Input for Switching Regulator 3.  
Linear Technology step-down switching regulator. An  
This pin will generally be connected to V . A 1μF MLCC  
OUT  
external P-channel MOSFET is sometimes required to  
capacitor is recommended on this pin.  
provide power to V  
with its gate tied to the ACPR pin  
OUT  
SW3 (Pin 17): Power Transmission Pin for Switching  
(seetheApplicationsInformationsection). Inconcertwith  
Regulator 3.  
WALL and ACPR, it will regulate V  
charger efficiency  
to maximize battery  
OUT  
NC (Pin 18): Unconnected Pin. This pin is not connected  
internally to the part. It is permissible to tie this pin to SW3  
in order to make the SW3 PCB trace wider.  
WALL(Pin27):ExternalPowerSourceSenseInput.WALL  
should be connected to the output of the external high  
voltage switching regulator and to the drain of an external  
P-channel MOSFET if used. It is used to determine when  
power is applied to the external regulator. When power  
is detected, ACPR is driven low and the USB input is au-  
tomatically disabled. Pulling this pin above 4.3V enables  
EN3 (Pin 19): Logic Input. This logic input pin indepen-  
dently enables switching regulator 3. Active high. This  
pin is logically ORed with its corresponding bit in the  
2
I C serial port. See Table 3. Has a 2μA internal pull-down  
current source.  
the V pin.  
C
FB3 (Pin 20): Feedback Input for Switching Regulator 3.  
Whenregulator3scontrolloopiscomplete,thispinservos  
to 1 of 16 possible set points based on the commanded  
2
value from the I C serial port. See Table 4.  
3576fb  
14  
LTC3576/LTC3576-1  
PIN FUNCTIONS  
BAT (Pin 32): Single Cell Li-Ion Battery Pin. Depending on  
ACPR (Pin 28): External Power Source Present Output  
(ActiveLow).ACPRindicatesthattheoutputoftheexternal  
high voltage step-down switching regulator is suitable for  
use by the LTC3576/LTC3576-1. It should be connected to  
the gate of an external P-channel MOSFET whose source  
available V  
power, a Li-Ion battery on BAT will either  
BUS  
deliverpowertoV throughtheidealdiodeorbecharged  
OUT  
from V  
via the battery charger.  
OUT  
VOUT (Pin 33): Output Voltage of the Bidirectional  
PowerPath Switching Regulator in step-down mode and  
Input Voltage of the Battery Charger. The majority of the  
portable product should be powered from VOUT. The  
LTC3576/LTC3576-1 will partition the available power  
between the external load on VOUT and the internal bat-  
tery charger. Priority is given to the external load and any  
extra power is used to charge the battery. An ideal diode  
from BAT to VOUT ensures that VOUT is powered even if  
the load exceeds the allotted power from VBUS or if the  
VBUS power source is removed. In on-the-go mode, this  
pin delivers power to VBUS via the SW pin. VOUT should  
be bypassed with a low impedance ceramic capacitor.  
is connected to V  
and whose drain is connected to  
OUT  
WALL. ACPR has a high level of V  
and a low level of  
OUT  
GND. The USB bidirectional switcher is disabled when  
ACPR is low.  
PROG (Pin 29): Charge Current Program and Charge Cur-  
rent Monitor Pin. Connecting a 1% resistor from PROG  
to ground programs the charge current. If sufficient input  
powerisavailableinconstant-currentmode,thispinservos  
to 1V. The voltage on this pin always represents the actual  
charge current by using the following formula:  
VPROG  
RPROG  
IBAT  
=
1030  
V
(Pins 34, 35): Power Pins. These pins deliver power  
OUT  
BUS  
to V  
via the SW pin by drawing controlled current from  
CHRG (Pin 30): Open-Drain Charge Status Output. The  
CHRG pin indicates the status of the battery charger.  
Four possible charger states are represented by CHRG:  
charging, not charging, unresponsive battery and battery  
temperature out of range. In addition, CHRG is used to  
a DC source such as a USB port or DC output wall adapter.  
In on-the-go mode these pins provide power to external  
loads.TiethetwoV  
pinstogetheratthepartandbypass  
BUS  
with a low impedance multilayer ceramic capacitor.  
indicate whether there is a short-circuit condition on V  
BUS  
SW (Pin 36): The SW pin transfers power between V  
BUS  
when the bidirectional switching regulator is in step-up  
mode (on-the-go). CHRG is modulated at 35kHz and  
switches between a low and a high duty cycle for easy  
recognition by either humans or microprocessors. See  
Table 1. CHRG requires a pull-up resistor and/or LED to  
provide indication.  
and V  
via the bidirectional switching regulator. See  
OUT  
the Applications Information section for a discussion of  
inductance value and current rating.  
I
,I  
(Pins37,38):I  
andI  
controlthecurrent  
LIM0 LIM1  
LIM0  
LIM1  
limit of the PowerPath switching regulator. See Table 1.  
Both the I  
and I  
pins are logically ORed with their  
LIM0  
LIM1  
2
IDGATE (Pin 31): Ideal Diode Amplifier Output. This pin  
correspondingbitsintheI Cserialport.SeeTables3and6.  
Each has a 2μA internal pull-down current source.  
controlsthegateofanoptionalexternalP-channelMOSFET  
used as an ideal diode between V  
and BAT. The external  
OUT  
Exposed Pad (Pin 39): Ground. The Exposed Pad should  
be connected to a continuous ground plane on the second  
layer of the printed circuit board by several vias directly  
under the LTC3576/LTC3576-1.  
idealdiodeoperatesinparallelwiththeinternalidealdiode.  
ThesourceoftheP-channelMOSFETshouldbeconnected  
to V  
and the drain should be connected to BAT. If the  
OUT  
external ideal diode MOSFET is not used, IDGATE should  
be left floating.  
3576fb  
15  
LTC3576/LTC3576-1  
BLOCK DIAGRAM  
V
C
26  
OVSENS  
OVGATE  
6
OVP  
5
27 WALL  
V
WALL  
DETECT  
C
V
V
35  
34  
BUS  
BUS  
CONTROL  
ACPR  
28  
2.25MHz  
BIDIRECTIONAL  
PowerPath  
SWITCHING  
REGULATOR  
SW  
36  
2
LDO3V3  
3.3V LDO  
SUSPEND LDO  
V
33  
31  
OUT  
500μA/2.5mA  
+
+
+
IDGATE  
IDEAL  
CC/CV  
CLPROG  
1
CHARGER  
+
+
5.1V  
NTCBIAS  
NTC  
3
4
BATTERY  
TEMPERATURE  
MONITOR  
15mV  
0.3V  
+
+
BAT  
32  
29  
3.6V  
1.18V  
OR 1.15V  
PROG  
CHRG 30  
CHARGE  
STATUS  
V
8
9
IN1  
ENABLE  
SW1  
FB1  
400mA 2.25MHz  
BUCK  
D/A  
D/A  
D/A  
REGULATOR  
7
4
V
24  
IN2  
ENABLE  
23 SW2  
400mA 2.25MHz  
BUCK  
REGULATOR  
FB2  
25  
16  
4
I
LIM  
DECODE  
LOGIC  
V
IN3  
ENABLE  
17 SW3  
1A 2.25MHz  
BUCK  
REGULATOR  
I
37  
38  
LIM0  
FB3  
20  
21  
I
LIM1  
4
RST3  
ENOTG 11  
EN1 10  
EN2 22  
EN3 19  
DV 12  
CC  
2
SDA 14  
SCL 13  
I C PORT  
39  
3576 BD  
GND  
3576fb  
16  
LTC3576/LTC3576-1  
TIMING DIAGRAM  
SDA  
t
t
t
SU,DAT  
SU,STA  
BUF  
t
SU,STO  
t
t
t
LOW  
HD,STA  
HD,DAT  
3208 F05  
SCL  
t
t
SP  
t
HIGH  
HD,STA  
START  
CONDITION  
REPEATED START  
CONDITION  
STOP  
CONDITION  
START  
CONDITION  
t
r
t
f
I2C WRITE PROTOCOL  
WRITE ADDRESS  
R/W  
SUB-ADDRESS  
INPUT DATA BYTE  
0
0
0
1
0
0
1
1
0
A7  
1
A6  
2
A5  
3
A4  
A3  
A2  
6
A1  
7
A0  
8
B7  
1
B6  
2
B5  
B4  
B3  
B2  
B1  
7
B0  
START  
STOP  
SDA  
SCL  
0
0
0
1
0
0
0
8
ACK  
9
ACK  
9
ACK  
9
1
2
3
4
5
6
7
4
5
3
4
5
6
8
3576 I2C  
3576fb  
17  
LTC3576/LTC3576-1  
OPERATION  
Introduction  
For automotive, firewire, and other high voltage applica-  
tions,theLTC3576/LTC3576-1provideBat-Trackcontrolof  
anexternalLTCstep-downswitchingregulatortomaximize  
battery charger efficiency and minimize heat production.  
WhenpowerisavailablefromboththeUSBandanauxiliary  
input, the auxiliary input is given priority.  
TheLTC3576/LTC3576-1arehighlyintegratedpowerman-  
agement ICs designed to make optimal use of the power  
availablefromavarietyofsources,whileminimizingpower  
dissipation and easing thermal budgeting constraints.  
They include a high efficiency bidirectional PowerPath  
switching regulator, a controller for an external high volt-  
age step-down switching regulator, a battery charger, an  
ideal diode, an always-on LDO, an overvoltage protection  
circuit and three general purpose step-down switching  
regulators. The entire chip is controlled by either direct  
The LTC3576/LTC3576-1 contain both an internal 180mΩ  
ideal diode as well as an ideal diode controller for use  
with an optional external P-channel MOSFET. The ideal  
diode(s) from BAT to V  
guarantee that ample power  
even if there is insufficient or  
OUT  
is always available to V  
absent power at V  
OUT  
2
digital control or by an I C serial port or both.  
or WALL.  
BUS  
The innovative PowerPath architecture ensures that the  
applicationispoweredimmediatelyafterexternalvoltageis  
applied,evenwithacompletelydeadbattery,byprioritizing  
power to the application.  
An always-on LDO provides a regulated 3.3V from avail-  
able power at V . Drawing very little quiescent current,  
OUT  
this LDO will be on at all times and can be used to supply  
20mA.  
When acting as a step-down converter, the LTC3576/  
LTC3576-1’s bidirectional switching regulator takes  
power from USB, wall adapters, or other 5V sources and  
provides power to the application and efficiently charges  
the battery using Bat-Track. Because power is conserved  
TheLTC3576/LTC3576-1featureanovervoltageprotection  
circuit which is designed to work with an external N-chan-  
nel MOSFET to prevent damage to their inputs caused by  
accidental application of high voltage.  
To prevent battery drain when a device is connected to a  
the LTC3576/LTC3576-1 allow the load current on V  
to  
OUT  
suspended USB port, an LDO from V  
to V  
provides  
BUS  
OUT  
exceed the current drawn by the USB port making maxi-  
mumuseoftheallowableUSBpowerforbatterycharging.  
For USB compatibility the switching regulator includes  
a precision average input current limit. The PowerPath  
switching regulator and battery charger communicate to  
ensure that the average input current never exceeds the  
USB specifications.  
either low power or high power USB suspend current to  
the application.  
The three general purpose switching regulators can be  
independently enabled either by direct digital control or  
2
2
by operating the I C serial port. Under I C control, all  
three switching regulators have adjustable set points so  
that voltages can be reduced when high processor perfor-  
manceisnotneeded. AlongwithconstantfrequencyPWM  
mode, all three switching regulators have automatic Burst  
Mode operation and LDO modes for significantly reduced  
quiescent current under light load conditions.  
Additionally, the bidirectional switching regulator can also  
operate as a 5V synchronous step-up converter taking  
power from V  
and delivering up to 500mA to V  
OUT  
BUS  
without the need for any additional external components.  
This enables systems with USB dual-role transceivers to  
function as USB on-the-go dual-role devices. True output  
disconnect and average output current limit features are  
included for short-circuit protection.  
3576fb  
18  
LTC3576/LTC3576-1  
OPERATION  
Bidirectional PowerPath Switching Regulator—  
Step-Down Mode  
If the combined external load plus battery charge current  
is large enough to cause the switching regulator to reach  
the programmed input current limit, the battery charger  
will reduce its charge current by precisely the amount  
necessary to enable the external load to be satisfied. Even  
if the battery charge current is programmed to exceed the  
allowable USB current, the USB specification for average  
input current will not be violated; the battery charger will  
reduce its current as needed. Furthermore, if the load cur-  
The power delivered from V  
to V  
is controlled by  
BUS  
OUT  
a 2.25MHz constant frequency bidirectional switching  
regulator operating in step-down mode. V drives the  
OUT  
combination of the external load (step-down switching  
regulators 1, 2 and 3) and the battery charger. To meet the  
maximum USB load specification, the switching regulator  
contains a measurement and control system that ensures  
that the average input current remains below the level  
programmed at CLPROG.  
rent at V  
exceeds the programmed power from V  
,
OUT  
BUS  
load current will be drawn from the battery via the ideal  
diode(s) even when the battery charger is enabled.  
If the combined load does not cause the switching regu-  
lator to reach the programmed input current limit, V  
will track approximately 0.3V above the battery voltage.  
By keeping the voltage across the battery charger at this  
low level, power lost to the battery charger is minimized.  
Figure 1 shows the power flow in step-down mode.  
ThecurrentoutofCLPROGisaprecisefractionoftheV  
BUS  
OUT  
current. When a programming resistor and an averaging  
capacitor are connected from CLPROG to GND, the volt-  
age on CLPROG represents the average input current of  
the switching regulator. As the input current approaches  
the programmed limit, CLPROG reaches 1.18V and power  
delivered by the switching regulator is held constant.  
TO AUTOMOTIVE,  
FIREWIRE, ETC.  
HIGH VOLTAGE  
V
V
SW  
FB  
IN  
STEP-DOWN  
SWITCHING  
REGULATOR  
C
26  
27  
V
C
WALL  
OVERVOLTAGE PROTECTION  
OVSENS  
OVGATE  
+
+
+
V
6
5
OUT  
3.6V  
BAT + 0.3V 4.3V  
ACPR  
+
28  
6V  
s2  
+
Bat-Track HV CONTROL  
3.5V TO  
(BAT + 0.3V)  
TO SYSTEM LOAD  
TO USB  
OR WALL  
ADAPTER  
V
SW  
BUS  
35  
34  
36  
33  
V
BUS  
V
OUT  
PWM AND  
GATE DRIVE  
V
BUS  
IDEAL  
VOLTAGE  
DIODE  
CONTROLLER  
+
IDGATE  
OPTIONAL EXTERNAL  
IDEAL DIODE PMOS  
I
/N  
CONSTANT CURRENT  
CONSTANT VOLTAGE  
BATTERY CHARGER  
SWITCH  
OmV  
31  
32  
+
5V  
+
15mV  
+
+
+
0.3V  
CLPROG  
1.18V  
1
BAT  
+
3.6V  
AVERAGE V  
CURRENT LIMIT  
CONTROLLER  
INPUT  
V
VOLTAGE  
BUS  
OUT  
CONTROLLER  
+
SINGLE CELL  
Li-Ion  
3576 F01  
USB INPUT  
BATTERY POWER  
HV INPUT  
Figure 1. PowerPath Block Diagram—Power Available from USB/Wall Adapter  
3576fb  
19  
LTC3576/LTC3576-1  
OPERATION  
4.5  
4.2  
3.9  
3.6  
3.3  
3.0  
2.7  
2.4  
The input current limit is programmed by the I  
and  
LIM0  
2
I
pins or by the I C serial port. The input current limit  
LIM1  
has five possible settings ranging from the USB suspend  
limit of 500μA up to 1A for wall adapter applications. Two  
of these settings are specifically intended for use in the  
100mA and 500mA USB applications. Refer to Table 1 for  
current limit settings using the I  
Table 6 for current limit settings using the I C port.  
NO LOAD  
300mV  
and I  
pins and  
LIM0  
LIM1  
2
Table 1. USB Current Limit Settings Using ILIM0 and ILIM1  
I
I
USB SETTING  
LIM1  
LIM0  
3.6  
4.2  
2.4  
2.7  
3.0  
3.3  
3.9  
0
0
BAT (V)  
1× Mode (USB 100mA Limit)  
10× Mode (Wall 1A Limit)  
Low Power Suspend (USB 500μA Limit)  
5× Mode (USB 500mA Limit)  
3576 F02  
0
1
1
1
0
1
Figure 2. VOUT vs BAT  
For very low-battery voltages, the battery charger acts like  
a load and, due to limited input power, its current will tend  
When the switching regulator is activated, the average  
input current will be limited by the CLPROG programming  
resistor according to the following expression:  
to pull V  
OUT  
below the 3.6V instant-on voltage. To prevent  
from falling below this level, an undervoltage circuit  
OUT  
V
automatically detects that V  
is falling and reduces the  
OUT  
VCLPROG  
RCLPROG  
IVBUS =IVBUSQ  
where I  
LTC3576-1, V  
current limit, R  
+
• h  
(
+1  
battery charge current as needed. This reduction ensures  
that load current and voltage are always prioritized while  
allowing as much battery charge current as possible. See  
Battery Charger Over Programming in the Applications  
Information section.  
)
CLPROG  
is the quiescent current of the LTC3576/  
CLPROG  
VBUSQ  
is the CLPROG servo voltage in  
is the value of the programming  
is the ratio of the measured cur-  
CLPROG  
The voltage regulation loop is compensated by the ca-  
resistor and h  
rent at V  
CLPROG  
pacitance on V . A 10μF MLCC capacitor is required  
to the sample current delivered to CLPROG.  
OUT  
BUS  
for loop stability. Additional capacitance beyond this value  
Refer to the Electrical Characteristics table for values of  
, V and I . Given worst-case circuit  
will improve transient response.  
h
CLPROG CLPROG  
VBUSQ  
tolerances, the USB specification for the average input  
current in 100mA or 500mA mode will not be violated,  
AninternalundervoltagelockoutcircuitmonitorsV and  
BUS  
rises above  
keeps the switching regulator off until V  
BUS  
provided that R  
is 3.01k or greater.  
CLPROG  
4.30V and is about 200mV above the battery voltage.  
Hysteresis on the UVLO turns off the regulator if V  
While not in current limit, the switching regulator’s  
Bat-Track feature will set V to approximately 300mV  
BUS  
falls below 4V or to within 50mV of the battery voltage.  
OUT  
When this happens, system power at V  
from the battery via the ideal diode(s).  
will be drawn  
above the voltage at BAT. However, if the voltage at BAT  
OUT  
is below 3.3V, and the load requirement does not cause  
the switching regulator to exceed its current limit, V  
OUT  
Bidirectional PowerPath Switching Regulator—  
Step-Up Mode  
will regulate at a fixed 3.6V as shown in Figure 2. This  
instant-on operation will allow a portable product to run  
immediatelywhenpowerisappliedwithoutwaitingforthe  
battery to charge. If the load does exceed the current limit  
For USB on-the-go applications, the bidirectional  
PowerPathswitchingregulatoractsasastep-upconverter  
at V , V  
will range between the no-load voltage and  
todeliverpowerfromV  
toV .ThepowerfromV  
BUS OUT  
OUT  
BUS OUT  
slightly below the battery voltage, indicated by the shaded  
region of Figure 2.  
can come from the battery or the output of the external  
3576fb  
20  
LTC3576/LTC3576-1  
OPERATION  
TO AUTOMOTIVE,  
FIREWIRE, ETC.  
HIGH VOLTAGE  
STEP-DOWN  
SWITCHING  
REGULATOR  
V
V
SW  
FB  
IN  
C
26  
27  
V
WALL  
C
OVERVOLTAGE PROTECTION  
OVSENS  
+
+
+
V
6
5
OUT  
3.6V  
BAT + 0.3V 4.3V  
ACPR  
+
28  
6V  
OVGATE  
s2  
+
Bat-Track HV CONTROL  
3.5V TO  
(BAT + 0.3V)  
TO SYSTEM LOAD  
V
SW  
OUT  
BUS  
TO USB  
CABLE  
35  
34  
36  
33  
V
BUS  
V
PWM AND  
GATE DRIVE  
V
BUS  
IDEAL  
VOLTAGE  
DIODE  
CONTROLLER  
+
IDGATE  
OPTIONAL EXTERNAL  
IDEAL DIODE PMOS  
I
/N  
CONSTANT CURRENT  
CONSTANT VOLTAGE  
BATTERY CHARGER  
SWITCH  
OmV  
31  
32  
+
5V  
+
15mV  
+
+
+
0.3V  
CLPROG  
1.15V  
1
BAT  
+
3.6V  
AVERAGE V  
CURRENT LIMIT  
CONTROLLER  
OUTPUT  
V
VOLTAGE  
BUS  
OUT  
CONTROLLER  
+
SINGLE CELL  
Li-Ion  
3576 F03  
BATTERY POWER  
HV INPUT  
Figure 3. PowerPath Block Diagram—USB On-the-Go  
transient response. The V  
3% load regulation up to an output current of 500mA. At  
light loads, the switching regulator goes into Burst Mode  
operation. The regulator will deliver power to V  
reaches 5.1V after which the NMOS and PMOS switches  
shut off. The regulator delivers power again to V  
it falls below 5.1V.  
voltage has approximately  
high voltage switching regulator. As a step-up converter,  
the bidirectional switching regulator produces 5V on  
BUS  
BUS  
V
and is capable of delivering at least 500mA. USB  
until it  
on-the-go can be enabled by either the external control  
BUS  
2
pin, ENOTG, or via I C. Figure 3 shows the power flow  
once  
in step-up mode.  
BUS  
An undervoltage lockout circuit monitors V  
and pre-  
OUT  
The switching regulator features both peak inductor and  
average output current limit. The peak current mode  
architecture limits peak inductor current on a cycle-by-  
vents step-up conversion until V  
rises above 2.8V. To  
OUT  
preventbackdrivingofV  
wheninputpowerisavailable,  
BUS  
the V  
undervoltage lockout circuit prevents step-up  
BUS  
cycle basis. The peak current limit is equal to V /2ꢀ to  
conversion if V  
is greater than 4.3V at the time step-up  
BUS  
BUS  
a maximum of 1.8A so that in the event of a sudden short  
circuit, the current limit will fold back to a lower value.  
In step-up mode, the voltage on CLPROG represents the  
average output current of the switching regulator when  
a programming resistor and an averaging capacitor are  
connected from CLPROG to GND. With a 3.01k resistor  
on CLPROG, the bidirectional switching regulator has an  
output current limit of 680mA. As the output current ap-  
mode is enabled. The switching regulator is also designed  
to allow true output disconnect by eliminating body diode  
conduction of the internal PMOS switch. This allows V  
BUS  
to go to zero volts during a short-circuit condition or while  
shut down, drawing zero current from V  
.
OUT  
The voltage regulation loop is compensated by the capaci-  
tance on V . A 4.7μF MLCC is required for loop stability.  
BUS  
Additional capacitance beyond this value will improve  
3576fb  
21  
LTC3576/LTC3576-1  
OPERATION  
proachesthislimitCLPROGservosto1.15VandV  
falls  
WALL will rise toward this programmed output voltage.  
WhenWALLexceedsapproximately4.3V,ACPRisbrought  
low and the Bat-Track control of the LTC3576/LTC3576-1  
BUS  
there may not  
rapidly to V . When V  
is close to V  
OUT  
BUS  
OUT  
be sufficient negative slope on the inductor current when  
the PMOS switch is on to balance the rise in the inductor  
current when the NMOS switch is on. This will cause the  
inductor current to run away and the voltage on CLPROG  
to rise. When CLPROG reaches 1.2V the switching of the  
overdrives the local V control of the external high volt-  
C
age step-down switching regulator. Therefore, once the  
Bat-Track control is enabled, the output voltage is set in-  
dependent of the switching regulator feedback network.  
synchronous PMOS is terminated and V  
is applied  
OUT  
Bat-Trackcontrolprovidesasignificantefficiencyadvantage  
over the simple use of a 5V switching regulator output to  
statically to its gate. This ensures that the inductor current  
will have sufficient negative slope during the time current  
is flowing to the output. The PMOS will resume switching  
when CLPROG drops down to 1.15V.  
drive the battery charger. With a 5V output driving V  
battery charger efficiency is approximately:  
,
OUT  
V
5V  
BAT  
ηTOTAL = ηBUCK  
TheLTC3576/LTC3576-1maintainvoltageregulationeven  
if V  
is above V . This is achieved by disabling the  
OUT  
BUS  
PMOS switch. The PMOS switch is enabled when V  
BUS  
where  
η
BUCK  
istheefficiencyofthehighvoltageswitching  
rises above V  
below V  
+ 180mV and is disabled when it falls  
OUT  
regulator and 5V is the output voltage of the switching  
regulator. With a typical switching regulator efficiency of  
87% and a typical battery voltage of 3.8V, the total bat-  
tery charger efficiency is approximately 66%. Assuming  
a 1A charge current, 1.7W of power is dissipated just to  
charge the battery!  
+ 70mV to prevent the inductor current from  
OUT  
running away when not in current limit. Since the PMOS  
no longer acts as a low impedance switch in this mode,  
there will be more power dissipation within the IC. This  
will cause a sharp drop in efficiency.  
If V  
is less than 4V and the PMOS switch is disabled  
BUS  
With Bat-Track, battery charger efficiency is approxi-  
mately:  
for more than 7.2ms a short-circuit fault will be declared  
and the part will shut off. The CHRG pin will blink at 35kHz  
with a duty cycle that varies between 12% and 88% at a  
4Hz rate. See Table 2. To re-enable step-up mode, the  
ENOTG pin or, with ENOTG grounded, the B0 bit in the  
V
BAT  
ηTOTAL = ηBUCK  
V
BAT + 0.3V  
2
With the same assumptions as above, the total battery  
charger efficiency is approximately 81%. This example  
works out to less than 1W of power dissipation, or almost  
60% less heat.  
I C port must be cycled low and then high.  
Bat-Track Auxiliary High Voltage Switching Regulator  
Control  
See the Typical Applications section for complete circuits  
using the LT3480 and the LT3653 with Bat-Track control.  
The WALL, ACPR and  
V pins can be used in conjunction  
C
with an external high voltage step-down switching regula-  
tor such as the LT®3480 or the LT3653 to minimize heat  
production when operating from higher voltage sources,  
as shown in Figures 1 and 3. Bat-Track control circuitry  
regulatestheexternalswitchingregulator’soutputvoltage  
to the larger of (BAT + 300mV) or 3.6V. This maximizes  
battery charger efficiency while still allowing instant-on  
operation when the battery is deeply discharged.  
Ideal Diode(s) from BAT to V  
OUT  
TheLTC3576/LTC3576-1eachhaveaninternalidealdiodeas  
wellasacontrollerforanoptionalexternalidealdiode.Both  
the internal and the external ideal diodes are always on and  
will respond quickly whenever V  
drops below BAT.  
OUT  
If the load current increases beyond the power allowed  
from the switching regulator, additional power will be  
pulled from the battery via the ideal diode(s). Further-  
Thefeedbacknetworkofthehighvoltageregulatorshould  
be set to generate an output voltage between 4.5V and  
5.5V.Whenhighvoltageisappliedtotheexternalregulator,  
more, if power to V  
(USB or wall adapter) is removed,  
BUS  
3576fb  
22  
LTC3576/LTC3576-1  
OPERATION  
2200  
2000  
1800  
1600  
1400  
1200  
copy of the V  
current to the CLPROG pin, which will  
BUS  
VISHAY Si2333  
OPTIONAL EXTERNAL  
IDEAL DIODE  
servo to approximately 100mV in this mode. To remain  
compliant with the USB specification, the input to the LDO  
is current limited so that it will not exceed the low power  
LTC3576/  
LTC3576-1  
IDEAL DIODE  
or high power suspend specification. If the load on V  
OUT  
1000  
800  
600  
400  
200  
0
exceeds the suspend current limit, the additional current  
will come from the battery via the ideal diode(s).  
ON  
SEMICONDUCTOR  
MBRM120LT3  
3.3V Always-On LDO Supply  
The LTC3576/LTC3576-1 include a low quiescent current  
low dropout regulator that is always powered. This LDO  
can be used to provide power to a system pushbutton  
controller, standby microcontroller or real time clock. De-  
signed to deliver up to 20mA, the always-on LDO requires  
at least a 1ꢁF low impedance ceramic bypass capacitor  
0
120 180 240 300 360 420 480  
60  
FORWARD VOLTAGE (mV) (BAT – V  
)
OUT  
3576 F04  
Figure 4. Ideal Diode V-I Characteristics  
then all of the application power will be provided by the  
battery via the ideal diodes. The ideal diode(s) will be fast  
for compensation. The LDO is powered from V , and  
therefore will enter dropout at loads less than 20mA as  
OUT  
enough to keep V  
from drooping with only the stor-  
OUT  
age capacitance required for the switching regulator. The  
internal ideal diode consists of a precision amplifier that  
activates a large on-chip P-channel MOSFET whenever  
V
falls near 3.3V. If the LDO3V3 output is not used, it  
OUT  
should be disabled by connecting it to V  
.
OUT  
the voltage at V  
is approximately 15mV (V  
) below  
Battery Charger  
OUT  
FWD  
the voltage at BAT. Within the amplifier’s linear range, the  
small-signal resistance of the ideal diode will be quite low,  
keeping the forward drop near 15mV. At higher current  
levels, the MOSFET will be in full conduction.  
The LTC3576/LTC3576-1 include a constant-current/con-  
stant-voltage battery charger with automatic recharge,  
automatic termination by safety timer, low voltage trickle  
charging, bad cell detection and thermistor sensor input  
for out-of-temperature charge pausing.  
To supplement the internal ideal diode, an external  
P-channel MOSFET may be added from BAT to V . The  
OUT  
Battery Preconditioning  
IDGATE pin of the LTC3576/LTC3576-1 drives the gate of  
the external P-channel MOSFET for automatic ideal diode  
control. The source of the external P-channel MOSFET  
When a battery charge cycle begins, the battery charger  
first determines if the battery is deeply discharged. If the  
should be connected to V  
and the drain should be con-  
OUT  
batteryvoltageisbelowV ,typically2.85V,anautomatic  
TRKL  
nected to BAT. Capable of driving a 1nF load, the IDGATE  
pin can control an external P-channel MOSFET transistor  
having an on-resistance of 30mΩ or lower.  
trickle charge feature sets the battery charge current to  
10% of the programmed value. If the low voltage persists  
for more than 1/2 hour, the battery charger automatically  
terminates and indicates via the CHRG pin that the battery  
was unresponsive.  
Suspend LDO  
IftheLTC3576/LTC3576-1areconfiguredforUSBsuspend  
mode,thebidirectionalswitchingregulatorisdisabledand  
Oncethebatteryvoltageisabove2.85V,thechargerbegins  
charging in full power constant-current mode. The cur-  
thesuspendLDOprovidespowertotheV  
pin(presum-  
OUT  
rent delivered to the battery will try to reach 1030/R  
.
PROG  
ingthereispoweravailabletoV ). ThisLDOwillprevent  
BUS  
Depending on available input power and external load  
conditions, the battery charger may or may not be able  
to charge at the full programmed rate. The external load  
will always be prioritized over the battery charge current.  
the battery from running down when the portable product  
has access to a suspended USB port. Regulating at 4.6V,  
thisLDOonlybecomesactivewhentheswitchingconverter  
isdisabled (suspended). Thesuspend LDOsendsa scaled  
3576fb  
23  
LTC3576/LTC3576-1  
OPERATION  
Likewise, the USB current limit programming will always  
be observed and only additional power will be available to  
charge the battery. When system loads are light, battery  
charge current will be maximized.  
Ineithertheconstant-currentorconstant-voltagecharging  
modes, the voltage at the PROG pin will be proportional to  
the actual charge current delivered to the battery. There-  
fore, the actual charge current can be determined at any  
time by monitoring the PROG pin voltage and using the  
following equation:  
Charge Termination  
The battery charger has a built-in safety timer. When the  
voltage on the battery reaches the pre-programmed float  
voltage, the battery charger will regulate the battery volt-  
age and the charge current will decrease naturally. Once  
the battery charger detects that the battery has reached  
the float voltage, the four hour safety timer is started.  
After the safety timer expires, charging of the battery will  
discontinue and no more current will be delivered.  
VPROG  
RPROG  
IBAT  
=
•1030  
In many cases, the actual battery charge current, I , will  
BAT  
belowerthanI  
duetolimitedinputpoweravailableand  
CHG  
prioritization with the system load drawn from V  
.
OUT  
The Battery Charger Flow Chart illustrates the battery  
charger’s algorithm.  
Automatic Recharge  
Charge Status Indication  
After the battery charger terminates, it will remain off  
drawing only microamperes of current from the battery.  
If the portable product remains in this state long enough,  
thebatterywilleventuallyselfdischarge.Toensurethatthe  
batteryisalwaystoppedoff,achargecyclewillautomatically  
begin when the battery voltage falls below the recharge  
threshold which is typically 100mV less than the charger’s  
float voltage. In the event that the safety timer is running  
whenthebatteryvoltagefallsbelowtherechargethreshold,  
it will reset back to zero. To prevent brief excursions below  
the recharge threshold from resetting the safety timer, the  
battery voltage must be below the recharge threshold for  
more than 1ms. The charge cycle and safety timer will  
The CHRG pin indicates the status of the battery charger.  
Four possible states are represented by CHRG which  
include charging, not charging, unresponsive battery and  
battery temperature out of range.  
The signal at the CHRG pin can be easily recognized as  
one of the above four states by either a human or a mi-  
croprocessor. An open-drain output, the CHRG pin can  
drive an indicator LED through a current limiting resistor  
for human interfacing or simply a pull-up resistor for  
microprocessor interfacing.  
To make the CHRG pin easily recognized by both humans  
and microprocessors, the pin is either low for charging,  
high for not charging, or it is switched at high frequency  
(35kHz) to indicate the two possible faults, unresponsive  
battery and battery temperature out of range.  
also restart if the V  
UVLO cycles low and then high  
BUS  
(e.g., V  
is removed and then replaced), or if the battery  
BUS  
2
charger is cycled on and off by the I C port.  
Charge Current  
When charging begins, CHRG is pulled low and remains  
low for the duration of a normal charge cycle. When  
charging is complete, i.e., the BAT pin reaches the float  
voltage and the charge current has dropped to one-tenth  
oftheprogrammedvalue, theCHRGpinisreleased(Hi-Z).  
If a fault occurs, the pin is switched at 35kHz. While  
switching, its duty cycle is modulated between a high  
and low value at a very low frequency. The low and high  
duty cycles are disparate enough to make an LED appear  
to be on or off thus giving the appearance of “blinking”.  
The charge current is programmed using a single resis-  
tor from PROG to ground. 1/1030th of the battery charge  
current is sent to PROG which will attempt to servo to  
1.000V. Thus, the battery charge current will try to reach  
1030 times the current in the PROG pin. The program  
resistor and the charge current are calculated using the  
following equation:  
VPROG  
RPROG  
ICHG  
=
1030  
3576fb  
24  
LTC3576/LTC3576-1  
OPERATION  
Battery Charger Flow Chart  
POWER ON/  
ENABLE CHARGER  
CLEAR EVENT TIMER  
ASSERT CHRG LOW  
YES  
NTC OUT OF RANGE  
NO  
INHIBIT CHARGING  
PAUSE EVENT TIMER  
BAT < 2.85V  
BAT > V  
E  
FLOAT  
BATTERY STATE  
2.85V < BAT < V  
E  
FLOAT  
YES  
CHRG CURRENTLY  
HIGH-Z  
CHARGE WITH  
FIXED VOLTAGE  
(V  
CHARGE AT  
100V/R (C/10 RATE)  
CHARGE AT  
1030V/R  
PROG  
RATE  
PROG  
)
FLOAT  
NO  
INDICATE  
NTC FAULT  
AT CHRG  
RUN EVENT TIMER  
PAUSE EVENT TIMER  
RUN EVENT TIMER  
TIMER > 4 HOURS  
NO  
NO  
TIMER > 30 MINUTES  
YES  
YES  
NO  
INHIBIT CHARGING  
STOP CHARGING  
I
< C/10  
YES  
BAT  
YES  
BAT RISING  
THROUGH  
RECHRG  
INDICATE BATTERY  
FAULT AT CHRG  
CHRG HIGH-Z  
CHRG HIGH-Z  
V
NO  
BAT FALLING  
THROUGH  
RECHRG  
NO  
NO  
YES  
BAT > 2.85V  
YES  
BAT < V  
RECHRG  
V
YES  
NO  
3576 FLOW  
3576fb  
25  
LTC3576/LTC3576-1  
OPERATION  
Each of the two faults has its own unique “blink” rate for  
human recognition as well as two unique duty cycles for  
machine recognition.  
In addition to charge status, the CHRG pin is also used  
to indicate whether there is a short-circuit condition on  
V
when the bidirectional switching regulator is in on-  
BUS  
the-go mode. When a short-circuit condition is detected,  
CHRG will blink with the same modulation frequency and  
duty cycle as a bad battery fault. If the charger is on at the  
same time that on-the-go is enabled, a 4Hz modulation of  
12% and 88% duty cycles on CHRG could indicate a bad  
The CHRG pin does not respond to the C/10 threshold  
if the LTC3576/LTC3576-1 is in V  
current limit. This  
BUS  
preventsfalseendofchargeindicationsduetoinsufficient  
power available to the battery charger.  
Table 2 illustrates the four possible states of the CHRG  
pin when the battery charger is active.  
battery or a short-circuit fault on V . System software  
BUS  
should turn off the charger or on-the-go to determine  
which fault has occurred.  
Table 2. CHRG Signal  
MODULATION  
Although very improbable, it is possible that a duty cycle  
reading could be taken at the bright-dim transition (low  
duty cycle to high duty cycle). When this happens the  
duty cycle reading will be precisely 50%. If the duty cycle  
reading is 50%, system software should disqualify it and  
take a new duty cycle reading.  
STATUS  
Charging  
FREQUENCY (BLINK) FREQUENCY  
DUTY CYCLES  
100%  
0Hz  
0Hz  
0Hz (Low-Z)  
0Hz (Hi-Z)  
Not Charging  
NTC Fault  
0%  
35kHz  
35kHz  
1Hz at 50%  
4Hz at 50%  
6%, 94%  
12%, 88%  
Bad Battery  
or On-The-Go  
Short-Circuit  
Fault  
NTC Thermistor  
The battery temperature is measured by placing a nega-  
tive temperature coefficient (NTC) thermistor close to the  
battery pack.  
An NTC fault is represented by a 35kHz pulse train whose  
duty cycle alternates between 6% and 94% at a 1Hz rate. A  
human will easily recognize the 1Hz rate as a “slow” blink-  
ing which indicates the out-of-range battery temperature  
while a microprocessor will be able to decode either the  
6% or 94% duty cycles as an NTC fault.  
To use this feature connect the NTC thermistor, R , be-  
NTC  
tween the NTC pin and ground and a bias resistor, R  
,
NOM  
from NTCBIAS to NTC. R  
should be a 1% 200ppm  
NOM  
resistor with a value equal to the value of the chosen NTC  
thermistor at 25°C (R25).  
If a battery is found to be unresponsive to charging (i.e.,  
its voltage remains below 2.85V for 1/2 hour), the CHRG  
pin gives the bad battery fault indication. For this fault, a  
human would easily recognize the 4Hz “fast” blink of the  
LEDwhileamicroprocessorwouldbeabletodecodeeither  
the 12% or 88% duty cycles as a bad battery fault.  
The LTC3576/LTC3576-1 pauses charging when the re-  
sistance of the NTC thermistor drops to 0.54 times the  
value of R25 or approximately 54k for a 100k thermistor.  
For a Vishay Curve 1 thermistor, this corresponds to ap-  
proximately 40°C. If the battery charger is in constant  
voltage (float) mode, the safety timer also pauses until the  
thermistor indicates a return to a valid temperature. As the  
temperature drops, the resistance of the NTC thermistor  
rises. The LTC3576/LTC3576-1 are also designed to pause  
charging when the value of the NTC thermistor increases  
to 3.25 times the value of R25. For a Vishay Curve 1  
100k thermistor, this resistance, 325k, corresponds to  
approximately 0°C. The hot and cold comparators each  
have approximately 3°C of hysteresis to prevent oscilla-  
tion about the trip point. Grounding the NTC pin disables  
all NTC functionality.  
Note that the LTC3576/LTC3576-1 are 3-terminal  
PowerPath products where system load is always priori-  
tized over battery charging. Due to excessive system load,  
there may not be sufficient power to charge the battery  
beyond the trickle charge threshold voltage within the bad  
battery timeout period. In this case, the battery charger  
will falsely indicate a bad battery. System software may  
then reduce the load and reset the battery charger to try  
again.  
3576fb  
26  
LTC3576/LTC3576-1  
OPERATION  
Thermal Regulation  
voltage is removed, the drain of the external MOSFET  
will return to 5V.  
To prevent thermal damage to the LTC3576/LTC3576-1 or  
surrounding components, an internal thermal feedback  
loop will automatically decrease the programmed charge  
current if the die temperature rises to 105°C. This thermal  
regulation technique protects the LTC3576/LTC3576-1  
from excessive temperature due to high power operation  
or high ambient thermal conditions, and allows the user  
to push the limits of the power handling capability with  
a given circuit board design. The benefit of the LTC3576/  
LTC3576-1 thermal regulation loop is that charge current  
can be set according to actual conditions rather than  
worst-case conditions for a given application with the  
assurance that the charger will automatically reduce the  
current in worst-case conditions.  
The charge pump output on OVGATE has limited output  
drive capability. Care must be taken to avoid leakage on  
this pin as it may adversely affect operation.  
SeetheApplicationsInformationsectionforresistorpower  
dissipation rating calculations, a table of recommended  
components, and examples of dual-input and reverse  
input protection.  
2
I C Interface  
The LTC3576/LTC3576-1 may receive commands from a  
2
host (master) using the standard 2-wire I C interface. The  
Timing Diagram shows the timing relationship of the sig-  
nals on the bus. The two bus lines, SDA and SCL, must be  
HIGH when the bus is not in use. External pull-up resistors  
Overvoltage Protection  
2
or current sources, such as the LTC1694 I C accelerator,  
TheLTC3576/LTC3576-1canprotectitselffromtheinadver-  
are required on these lines. The LTC3576/LTC3576-1are  
2
tent application of excessive voltage to V  
or WALL with  
BUS  
receive-only slave devices. The I C control signals, SDA  
just two external components: an N-channel MOSFET and  
a 6.2k resistor. The maximum safe overvoltage magnitude  
will be determined by the choice of the external MOSFET  
and its associated drain breakdown voltage.  
and SCL are scaled internally to the DV supply. DV  
CC  
CC  
should be connected to the same power supply as the  
2
microcontroller generating the I C signals.  
2
The I C port has an undervoltage lockout on the DV  
CC  
2
The overvoltage protection module consists of two pins.  
The first, OVSENS, is used to measure the externally ap-  
plied voltage through an external resistor. The second,  
OVGATE, is an output used to drive the gate pin of the  
external MOSFET. When OVSENS is below 6V, an internal  
charge pump will drive OVGATE to approximately 1.88 ×  
OVSENS. This will enhance the N-channel MOSFET and  
provide a low impedance connection to VBUS or WALL  
which will, in turn, power the LTC3576/LTC3576-1. If  
OVSENS should rise above 6V due to a fault or use of  
an incorrect wall adapter, OVGATE will be pulled to GND  
disabling the external MOSFET and therefore protecting  
downstream circuitry. When the voltage drops below 6V  
again, the external MOSFET will be re-enabled.  
pin. When DV is below approximately 1V, the I C serial  
CC  
port is cleared and switching regulators 1, 2 and 3 are  
set to full scale.  
Bus Speed  
2
The I C port is designed to be operated at speeds of up  
to 400kHz. It has built-in timing delays to ensure correct  
2
operation when addressed from an I C compliant master  
device. It also contains input filters designed to suppress  
glitches should the bus become corrupted.  
Start and Stop Conditions  
A bus master signals the beginning of a communication  
to a slave device by transmitting a START condition. A  
START condition is generated by transitioning SDA from  
high to LOW while SCL is HIGH. When the master has  
finished communicating with the slave, it issues a STOP  
condition by transitioning SDA from LOW to HIGH while  
SCL is high. The bus is then free for communication with  
When USB on-the-go is enabled, the bidirectional switch-  
ingregulatorpowersuptheovervoltageprotectioncircuit  
through the body diode of the external MOSFET, thus pro-  
viding protection to the part even when VBUS is sourcing  
power. When high voltage is applied to the drain of the  
external MOSFET, VBUS will remain at 5V. Once the high  
2
another I C device.  
3576fb  
27  
LTC3576/LTC3576-1  
OPERATION  
Byte Format  
Bus Write Operation  
EachbytesenttotheLTC3576/LTC3576-1mustbeeightbits  
long followed by an extra clock cycle for the acknowledge  
bit. The data should be sent to the LTC3576/LTC3576-1  
with the most significant bit (MSB) first.  
The master initiates communication with the LTC3576/  
LTC3576-1 with a START condition and a 7-bit address  
followed by the R/W bit = 0. If the address matches that  
oftheLTC3576/LTC3576-1,theLTC3576/LTC3576-1return  
an acknowledge. The master should then deliver the sub-  
address. Again the LTC3576/LTC3576-1 acknowledge and  
the cycle is repeated for the data byte. The data byte is  
transferredtoaninternalholdinglatchuponthereturnofits  
acknowledge by the LTC3576/LTC3576-1. This procedure  
must be repeated for each sub-address that requires new  
data. After one or more data bytes have been transferred  
to the LTC3576/LTC3576-1, the master may terminate the  
communication with a STOP condition. Alternatively, a  
repeated START condition can be initiated by the master  
Acknowledge  
The acknowledge signal is used for handshaking between  
the master and the slave. An acknowledge (active low)  
generatedbytheslave(LTC3576/LTC3576-1)letsthemas-  
ter know that the latest byte of information was received.  
The acknowledge related clock pulse is generated by the  
master. The master releases the SDA line (HIGH) during  
the acknowledge clock cycle. The slave-receiver must pull  
down the SDA line during the acknowledge clock pulse  
so that it remains a stable LOW during the HIGH period  
of this clock pulse.  
2
and another chip on the I C bus can be addressed. This  
cyclecancontinueindefinitelyandtheLTC3576/LTC3576-1  
remembers the last input of valid data that it received.  
Once all chips on the bus have been addressed and sent  
valid data, a global STOP condition can be sent and the  
LTC3576/LTC3576-1 will update their command latches  
with the data that they have received.  
Slave Address  
The address byte consists of the 7-bit address and the  
read/write (R/W) bit. The LTC3576/LTC3576-1 respond to  
onlyone7-bitaddresswhichhasbeenfactoryprogrammed  
to 0001001. The R/W bit is the least significant bit of the  
address byte. It must be 0 for the LTC3576/LTC3576-1 to  
recognize the address since they are write only devices.  
Thus the address byte is 0x12. If the correct seven bit ad-  
dressisgivenbuttheR/Wbitis1,theLTC3576/LTC3576-1  
will not respond.  
2
In certain circumstances the data on the I C bus may be-  
come corrupted. In these cases, the LTC3576/LTC3576-1  
respond appropriately by preserving only the last set  
of complete data that they have received. For example,  
assume the LTC3576/LTC3576-1 have been successfully  
addressed and are receiving data when a STOP condition  
mistakenlyoccurs.TheLTC3576/LTC3576-1willignorethis  
STOP condition and will not respond until a new START  
condition, correct address and sub-address, new set of  
data and STOP condition are transmitted.  
Sub-Addressed Writing  
The LTC3576/LTC3576-1 have four command registers  
2
for control input. They are accessed by the I C port via a  
sub-addressed writing system.  
Likewise, with only one exception, if the LTC3576/  
LTC3576-1 were previously addressed and sent valid data  
but not updated with a STOP, they will respond to any  
STOP that appears on the bus, independent of the num-  
ber of repeated STARTs that have occurred. If a repeated  
START is given and the LTC3576/LTC3576-1 successfully  
acknowledge their address and sub-address, they will not  
respond to a STOP until a full byte of the new data has  
been received and acknowledged.  
Each write to the LTC3576/LTC3576-1 consists of three  
bytes. The first byte is always the LTC3576/LTC3576-1’s  
write address. The second byte represents the LTC3576/  
LTC3576-1’s sub-address. The sub-address acts as  
pointer to direct the subsequent data byte within the  
LTC3576/LTC3576-1.Thethirdbyteconsistsofthedatato  
be written to the location pointed to by the sub-address.  
The LTC3576/LTC3576-1 contain four sub-addresses at  
locations 0x00, 0x01, 0x02 and 0x03.  
3576fb  
28  
LTC3576/LTC3576-1  
OPERATION  
Input Data  
sub-address 1 controls the servo voltage of switching  
regulator 3 and the enable signals for all three switching  
regulators, as well as the enable signal for the PowerPath  
Table 3 illustrates the four data bytes that may be written  
to the LTC3576/LTC3576-1.  
switching regulator to power up V  
for USB on-the-go.  
BUS  
The first byte at sub-address 0 controls the servo volt-  
age for switching regulators 1 and 2. The second byte at  
The servo voltages are decoded in Table 4. The default  
servo voltage is 0.8V.  
Table 3. I2C Serial Port Mapping*  
A7  
A6  
A5  
A4  
A3  
A2  
A1  
A0  
B7  
B6  
B5  
B4  
B3  
B2  
B1  
B0  
Switching Regulator 1 Voltage  
(See Table 4)  
Switching Regulator 2 Voltage  
(See Table 4)  
Switching Regulator 3 Voltage  
(See Table 4)  
Reset Value  
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
C7  
C6  
C5  
C4  
C3  
C2  
C1  
C0  
D7  
D6  
D5  
D4  
D3  
D2  
D1  
D0  
Switching  
Switching  
Switching  
Input Current  
Limit  
(See Table 6)  
Unused  
Regulator 1  
Modes  
Regulator 2  
Modes  
Regulator 3  
Modes  
(See Table 5)  
(See Table 5)  
(See Table 5)  
Reset Value  
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
*The A7-A0 and B7-B4 bits default to 1 and all other bits default to 0 when the chip is powered and DV = 0.  
CC  
Table 4. Switching Regulator Servo Voltage  
A7  
A3  
B7  
0
A6  
A2  
B6  
0
A5  
A1  
B5  
0
A4  
A0  
B4  
0
Switching Regulator 1 Servo Voltage  
Switching Regulator 2 Servo Voltage  
Switching Regulator 3 Servo Voltage  
0.425  
0.450  
0.475  
0.500  
0.525  
0.550  
0.575  
0.600  
0.625  
0.650  
0.675  
0.700  
0.725  
0.750  
0.775  
0.800  
0
0
0
1
0
0
1
0
0
0
1
1
0
1
0
0
0
1
0
1
0
1
1
0
0
1
1
1
1
0
0
0
1
0
0
1
1
0
1
0
1
0
1
1
1
1
0
0
1
1
0
1
1
1
1
0
1
1
1
1
3576fb  
29  
LTC3576/LTC3576-1  
OPERATION  
2
Disabling the I C Port  
Thethirddatabyteatsub-address2controlstheoperating  
modes of each switching regulator as well as the input  
current limit settings. Each switching regulator can be  
independently set to one of three operating modes listed  
in Table 5.  
2
The I C serial port can be disabled by grounding the DV  
CC  
pin. In this mode, the LTC3576/LTC3576-1 are controlled  
through the individual logic input pins EN1, EN2, EN3,  
ENOTG, I  
, I  
, SDA and SCL. Some functionality is  
LIM0 LIM1  
not available in this mode such as the programmability of  
switchingregulators1,2and3soutputvoltage,thebattery  
chargerdisablefeatureandthehighpowersuspendmode.  
Inthismode,theprogrammableswitchingregulatorshave  
a fixed servo voltage of 0.8V. Because the SDA and SCL  
Table 5. General Purpose Switching Regulator Modes  
C7 (SDA)*  
C6 (SCL)* Switching Regulator 1 Mode  
C4 (SCL)* Switching Regulator 2 Mode  
C2 (SCL)* Switching Regulator 3 Mode  
C5 (SDA)*  
C3 (SDA)*  
0
1
1
X
0
1
Pulse-Skipping Mode  
LDO Mode  
pins have no other context when DV is grounded, these  
CC  
pins are re-mapped to control the switching regulator  
mode bits C2 to C7. SCL maps to C2, C4 and C6 while  
SDA maps to C3, C5 and C7.  
Burst Mode Operation  
*SDA and SCL take on this context only when DV = 0V.  
CC  
The input current limit settings are decoded according  
to Table 6. This table indicates the maximum current  
RST3 Pin  
that will be drawn from the V  
pin in the event that the  
BUS  
The RST3 pin is an open-drain output used to indicate that  
switching regulator 3 has been enabled and has reached  
itsnalvoltage.RST3remainslowimpedanceuntilregula-  
tor 3 reaches 92% of its regulation value.  
load at V  
(battery charger plus system load) exceeds  
OUT  
the power available. Any additional power will be drawn  
from the battery. The start-up state for the input current  
limit setting is 00 representing the low power 100mA  
USB setting.  
A230msdelayisincludedtoallowasystemmicrocontroller  
ample time to reset itself. RST3 may be used as a power-  
on reset to the microprocessor powered by regulator 3  
or may be used to enable regulators 1 and/or 2 for supply  
sequencing. RST3 is an open-drain output and requires  
a pull-up resistor to the output voltage of regulator 3 or  
another appropriate power source.  
Table 6. USB Current Limit Settings  
C1  
LIM1  
0
C0  
LIM0  
0
D6  
X
(I  
)* (I  
)* USB SETTING  
1× Mode (USB 100mA Limit)  
X
0
1
1
1
1
0
0
1
10× Mode (Wall 1A Limit)  
0
Low Power Suspend (USB 500μA Limit)  
High Power Suspend (USB 2.5mA Limit)  
5× Mode (USB 500mA Limit)  
1
Shutdown Mode  
X
The bidirectional USB switching regulator in step-down  
*I  
and I  
can only be used to enable the low power suspend mode  
LIM1  
LIM0  
mode is enabled whenever V  
is above V  
and the  
and are logically ORed with C1 and C0, respectively.  
BUS  
UVLO  
LTC3576/LTC3576-1arenotinoneofthetwoUSBsuspend  
modes (500μA or 2.5mA). When power is available from  
boththeUSBandauxiliaryinputs,theauxiliaryinputisgiven  
priority and the USB switching regulator is disabled.  
The fourth and final byte of input data at sub-address 3  
providesbitsfordisablingthebatterychargerandenabling  
the high power suspend mode current limit of 2.5mA.  
The ideal diode(s) are enabled at all times and cannot be  
disabled.  
3576fb  
30  
LTC3576/LTC3576-1  
OPERATION  
Step-Down Switching Regulators  
Step-Down Switching Regulator Operating Modes  
The LTC3576/LTC3576-1 contain three general purpose  
2.25MHz step-down constant-frequency current mode  
switchingregulators. Tworegulatorsprovideupto400mA  
and a third switching regulator can provide up to 1A.  
All three switching regulators can be programmed for  
a minimum start-up output voltage of 0.8V and can be  
used to power a microcontroller core, microcontroller  
I/O, memory, disk drive or other logic circuitry. All three  
The LTC3576/LTC3576-1’s general purpose switching  
regulatorsincludethreepossibleoperatingmodestomeet  
the noise/power needs of a variety of applications.  
In pulse-skipping mode, an internal latch is set at the start  
ofeverycyclewhichturnsonthemainP-channelMOSFET  
switch.Duringeachcycle,acurrentcomparatorcompares  
thepeakinductorcurrenttotheoutputofanerroramplifier.  
The output of the current comparator resets the internal  
latch which causes the main P-channel MOSFET switch to  
turn off and the N-channel MOSFET synchronous rectifier  
to turn on. The N-channel MOSFET synchronous rectifier  
turns off at the end of the 2.25MHz cycle or if the current  
through the N-channel MOSFET synchronous rectifier  
drops to zero. Using this method of operation, the error  
amplifier adjusts the peak inductor current to deliver the  
required output power. All necessary compensation is  
internal to the switching regulator requiring only a single  
ceramicoutputcapacitorforstability.AtlightloadsinPWM  
mode, the inductor current may reach zero on each pulse  
which will turn off the N-channel MOSFET synchronous  
rectifier. In this case, the switch node (SW) goes high  
impedance and the switch node voltage will “ring”. This  
is discontinuous mode operation, and is normal behavior  
for a switching regulator. At very light loads in pulse-skip-  
pingmode,theswitchingregulatorswillautomaticallyskip  
pulses as needed to maintain output regulation.  
2
switchingregulatorshaveI Cprogrammablesetpointsfor  
on-the-fly power savings. They also support 100% duty  
cycle operation (low dropout mode) when their input volt-  
agedropsveryclosetotheiroutputvoltage.Tosuitavariety  
of applications, selectable mode functions can be used to  
trade off noise for efficiency. Three modes are available to  
control the operation of the LTC3576/LTC3576-1’s general  
purposeswitchingregulators.Atmoderatetoheavyloads,  
the pulse skip mode provides the lowest noise switching  
solution. At lighter loads, Burst Mode operation or LDO  
mode may be selected. The switching regulators include  
soft-start to limit inrush current when powering on, short-  
circuit current protection and switch node slew limiting  
circuitry to reduce radiated EMI. No external compensa-  
tion components are required. The operating mode of the  
2
regulators may be set by either I C control or by manual  
2
control of the SDA and SCL pins if the I C port is not used.  
Each converter may be individually enabled by either their  
2
external control pins EN1, EN2, EN3 or by the I C port. All  
At high duty cycles (V  
> V /2) it is possible for the  
INx  
three switching regulators have individual programmable  
OUTx  
2
inductorcurrenttoreverse,causingtheregulatortooperate  
continuouslyatlightloads.Thisisnormalandregulationis  
maintained, but the supply current will increase to several  
mA due to continuous switching.  
feedback servo voltages via I C control. The switching  
regulator input supplies V , V and V will generally  
IN1 IN2  
IN3  
be connected to the system load pin V  
.
OUT  
3576fb  
31  
LTC3576/LTC3576-1  
OPERATION  
InBurstModeoperation,theswitchingregulatorautomati-  
callyswitchesbetweenxedfrequencyPWMoperationand  
hystereticcontrolasafunctionoftheloadcurrent. Atlight  
loads, the regulator operates in hysteretic mode and uses  
a constant current algorithm to control the inductor cur-  
rent. While in Burst Mode operation, the output capacitor  
is charged to a voltage slightly higher than the regulation  
point. The step-down switching regulator then goes into  
sleep mode, during which the output capacitor provides  
the load current. In sleep mode, most of the regulator’s  
circuitry is powered down, conserving battery power.  
When the output voltage drops below a pre-determined  
value, the switching regulator circuitry is powered on and  
another burst cycle begins. The duration for which the  
regulator operates in sleep mode depends on the load  
current. The sleep time decreases as the load current  
increases. Burst Mode operation provides a significant  
improvement in efficiency at light loads at the expense  
of higher output ripple when compared to pulse-skipping  
mode. At heavy loads Burst Mode operation functions in  
the same manner as pulse-skipping mode.  
dropoutcondition,therespectiveoutputvoltageequalsthe  
regulator’s input voltage minus the voltage drops across  
the internal P-channel MOSFET and the inductor.  
Step-Down Switching Regulator Low Supply Operation  
The LTC3576/LTC3576-1 incorporate an undervoltage  
lockout circuit on V  
which shuts down the general  
OUT  
purpose switching regulators when V  
drops below  
OUT  
V . This UVLO prevents unstable operation.  
OUT(UVLO)  
Step-Down Switching Regulator Soft-Start Operation  
Soft-start is accomplished by gradually increasing the  
peak inductor current for each switching regulator over a  
500ꢁs period. This allows each output to rise slowly, help-  
ing minimize the battery surge current. A soft-start cycle  
occurs whenever a given switching regulator is enabled,  
or after a fault condition has occurred (thermal shutdown  
or UVLO). A soft-start cycle is not triggered by changing  
operating modes. This allows seamless output operation  
when transitioning between Burst Mode operation, pulse-  
skipping mode or LDO mode.  
Finally, the switching regulators have an LDO mode that  
gives a DC option for regulating their output voltages. In  
LDOmode,theswitchingregulatorsareconvertedtolinear  
regulators and deliver continuous power from their SWx  
pins through their respective inductors. This mode gives  
the lowest possible output noise as well as low quiescent  
current at light loads.  
Step-Down Switching Regulator Switching  
Slew Rate Control  
The step-down switching regulators contain new patent  
pending circuitry to limit the slew rate of the switch node  
(SWx). This new circuitry is designed to transition the  
switch node over a period of a couple of nanoseconds,  
significantly reducing radiated EMI and conducted supply  
noise.  
Thestep-downswitchingregulatorsallowon-the-flymode  
transitions,providingseamlesstransitionbetweenmodes  
even under load. This allows the user to switch back and  
forth between modes to reduce output ripple or increase  
low current efficiency as needed.  
Step-Down Switching Regulator in Shutdown  
Thestep-downswitchingregulatorsareinshutdownwhen  
not enabled for operation. In shutdown, all circuitry in  
the step-down switching regulator is disconnected from  
the switching regulator input supply leaving only a few  
nanoamperesofleakagecurrent.Thestep-downswitching  
regulatoroutputsareindividuallypulledtogroundthrough  
a 10k resistor on their SWx pins when in shutdown.  
Step-Down Switching Regulator Dropout Operation  
It is possible for a switching regulator’s input voltage,  
V
, to approach its programmed output voltage (e.g., a  
INx  
battery voltage of 3.4V with a programmed output voltage  
of 3.3V). When this happens, the PMOS switch duty cycle  
increasesuntilitisturnedoncontinuouslyat100%.Inthis  
3576fb  
32  
LTC3576/LTC3576-1  
APPLICATIONS INFORMATION  
Bidirectional PowerPath Switching Regulator  
CLPROG Resistor and Capacitor Selection  
Bidirectional PowerPath Switching Regulator V  
BUS  
and V  
Bypass Capacitor Selection  
OUT  
The type and value of capacitors used with the LTC3576/  
LTC3576-1 determine several important parameters such  
asregulatorcontrol-loopstabilityandinputvoltageripple.  
Because the LTC3576/LTC3576-1 use a bidirectional  
As described in the Bidirectional Switching Regula-  
tor—Step-Down Mode section, the resistor on the  
CLPROG pin determines the average V  
input current  
BUS  
limit when the switching regulator is set to either the 1×  
switching regulator between V  
and V , the V  
mode (USB 100mA), the 5× mode (USB 500mA) or the  
BUS  
OUT BUS  
current waveform contains high frequency components.  
It is strongly recommended that a low equivalent series  
resistance (ESR) multilayer ceramic capacitor (MLCC) be  
10× mode. The V  
input current will be comprised of  
BUS  
two components, the current that is used to drive V  
OUT  
and the quiescent current of the switching regulator. To  
ensure that the USB specification is strictly met, both  
components of the input current should be considered.  
The Electrical Characteristics table gives the typical values  
forquiescentcurrentsinallsettingsaswellascurrentlimit  
programming accuracy. To get as close to the 500mA or  
100mA specifications as possible, a precision resistor  
should be used. Recall that:  
used to bypass V . Tantalum and aluminum capacitors  
BUS  
arenotrecommendedbecauseoftheirhighESR.Thevalue  
of the capacitor on V  
directly controls the amount of  
BUS  
input ripple for a given load current. Increasing the size  
of this capacitor will reduce the input ripple.  
The inrush current limit specification for USB devices is  
calculatedintermsofthetotalnumberofCoulombsneeded  
to charge the V  
bypass capacitor to 5V. The maximum  
I
= I  
+ V  
/R  
• (h  
+1).  
BUS  
VBUS  
VBUSQ  
CLPROG CLPPROG  
CLPROG  
inrush charge for USB on-the-go devices is 33μC. This  
places a limit of 6.5μF of capacitance on V assuming  
An averaging capacitor is required in parallel with the  
resistor so that the switching regulator can determine the  
average input current. This capacitor also provides the  
dominant pole for the feedback loop when current limit  
is reached. To ensure stability, the capacitor on CLPROG  
should be 0.1μF or larger.  
BUS  
a linear capacitor. However, most ceramic capacitors have  
a capacitance that varies with bias voltage. The average  
capacitanceneedstobelessthan6.5μFovera0Vto5Vbias  
voltagerangetomeettheinrushcurrentlimitspecification.  
A 10μF capacitor in a 0805 package, such as the Murata  
GRM21BR71A106KE51LwouldbeasuitableV  
bypass  
BUS  
Bidirectional PowerPath Switching Regulator  
Inductor Selection  
capacitor. If more capacitance is required for better noise  
performanceandstabilityitshouldbeconnecteddirectlyto  
Because the input voltage range and output voltage range  
of the PowerPath switching regulator are both fairly nar-  
row, the LTC3576/LTC3576-1 were designed for a specific  
inductance value of 3.3μH. Some inductors which may be  
suitable for this application are listed in Table 7.  
theV  
pinwhenusingtheovervoltageprotectioncircuit.  
BUS  
This extra capacitance will be soft-connected over several  
milliseconds to limit inrush current and avoid excessive  
transient voltage drops on V  
.
BUS  
To prevent large V  
voltage steps during transient load  
OUT  
Table 7. Recommended PowerPath Inductors for the LTC3576  
MAX MAX  
conditions, it is also recommended that an MLCC be used  
to bypass V . The output capacitor is used in the com-  
OUT  
INDUCTOR  
TYPE  
L
I
DCR SIZE IN mm  
(Ω) (L × W × H) MANUFACTURER  
DC  
pensation of the switching regulator. At least 10μF with  
(μH) (A)  
low ESR are required on V . Additional capacitance will  
OUT  
LPS4018  
3.3 2.2 0.08  
Coilcraft  
www.coilcraft.com  
3.9 × 3.9 × 1.7  
improve load transient performance and stability.  
D53LC  
3.3 2.26 0.034  
3.3 1.55 0.070  
Toko  
5 × 5 × 3  
MLCCs typically have exceptional ESR performance.  
MLCCscombinedwithatightboardlayoutandanunbroken  
ground plane will yield very good performance and low  
EMI emissions.  
DB318C  
www.toko.com  
3.8 × 3.8 × 1.8  
WE-TPC  
Type M1  
3.3 1.95 0.065  
Wurth Electronik  
www.we-online.com  
4.8 × 4.8 × 1.8  
CDRH6D12  
CDRH6D38  
3.3  
3.3  
2.2 0.063  
3.5 0.020  
Sumida  
www.sumida.com  
6.7 × 6.7 × 1.5  
7 × 7 × 4  
3576fb  
33  
LTC3576/LTC3576-1  
APPLICATIONS INFORMATION  
ThereareMLCCsavailablewithseveraltypesofdielectrics  
each having considerably different characteristics. For  
example, X7R MLCCs have the best voltage and tempera-  
ture stability. X5R MLCCs have apparently higher packing  
density but poorer performance over their rated voltage  
and temperature ranges. Y5V MLCCs have the highest  
packing density, but must be used with caution, because  
of their extreme nonlinear characteristic of capacitance  
versus voltage. The actual in-circuit capacitance of a  
ceramic capacitor should be measured with a small AC  
signal and DC bias as is expected in-circuit. Many vendors  
to improve transient response for output voltages much  
greater than 0.8V. A variety of capacitor sizes can be used  
for C but a value of 10pF is recommended for most ap-  
FB  
plications. Experimentation with capacitor sizes between  
2pF and 22pF may yield improved transient response.  
Step-Down Switching Regulator Inductor Selection  
Many different sizes and shapes of inductors are avail-  
able from numerous manufacturers. Choosing the right  
inductor from such a large selection of devices can be  
overwhelming, but following a few basic guidelines will  
make the selection process much simpler.  
specify the capacitance versus voltage with a 1V  
AC  
RMS  
test signal and, as a result, over state the capacitance that  
the capacitor will present in the application. Using similar  
operating conditions as the application, the user must  
measureorrequestfromthevendortheactualcapacitance  
to determine if the selected capacitor meets the minimum  
capacitance that the application requires.  
Thegeneralpurposestep-downconvertersaredesignedto  
work with inductors in the range of 2ꢁH to 10ꢁH. For most  
applications a 4.7ꢁH inductor is suggested for the lower  
current switching regulators 1 and 2 and 2ꢁH is recom-  
mendedforthehighercurrentswitchingregulator 3.Larger  
valueinductorsreduceripplecurrentwhichimprovesout-  
put ripple voltage. Lower value inductors result in higher  
ripple current and improved transient response time. To  
maximize efficiency, choose an inductor with a low DC  
resistance. For a 1.2V output, efficiency is reduced about  
2% for 100mꢀ series resistance at 400mA load current,  
and about 2% for 300mꢀ series resistance at 100mA load  
current. Choose an inductor with a DC current rating at  
least 1.5 times larger than the maximum load current to  
ensure that the inductor does not saturate during normal  
operation. If output short circuit is a possible condition,  
the inductor should be rated to handle the maximum peak  
current specified for the step-down converters. Different  
core materials and shapes will change the size/current  
and price/current relationship of an inductor. Toroid or  
shielded pot cores in ferrite or Permalloy materials are  
small and don’t radiate much energy, but generally cost  
more than powdered iron core inductors with similar  
electrical characteristics. Inductors that are very thin or  
have a very small volume typically have much higher  
core and DCR losses, and will not give the best efficiency.  
The choice of which style inductor to use often depends  
more on the price vs size, performance and any radiated  
EMI requirements than on what the LTC3576/LTC3576-1  
require to operate.  
Step-Down Switching Regulator Output Voltage  
Programming  
2
All three switching regulators have I C programmable  
set points and can be programmed for start-up output  
voltages of at least 0.8V. The full-scale output voltage for  
each switching regulator is programmed using a resistor  
divider from the switching regulator output connected to  
the FBx pins such that:  
R1  
R2  
VOUTx = V  
+1  
FBx  
where V ranges from 0.425V to 0.8V. See Figure 5.  
FBx  
Typical values for R1 are in the range of 40k to 1M. The  
capacitorC cancelsthepolecreatedbyfeedbackresistors  
FB  
and the input capacitance of the FBx pin and also helps  
V
INx  
L
V
SWx  
OUTx  
LTC3576/  
C
R1  
C
OUT  
FB  
LTC3576-1  
FBx  
R2  
GND  
3576 F05  
Figure 5. Buck Converter Application Circuit  
3576fb  
34  
LTC3576/LTC3576-1  
APPLICATIONS INFORMATION  
The inductor value also has an effect on Burst Mode op-  
eration. Lower inductor values will cause the Burst Mode  
operation switching frequency to increase.  
tor is sufficient for most applications. For good transient  
response and stability the output capacitor should retain  
atleast4Fofcapacitanceoveroperatingtemperatureand  
biasvoltage.Eachswitchingregulatorinputsupplyshould  
be bypassed with a 1ꢁF capacitor. Consult with capacitor  
manufacturers for detailed information on their selection  
and specifications of ceramic capacitors. Many manufac-  
turers now offer very thin (<1mm tall) ceramic capacitors  
ideal for use in height-restricted designs. Table 9 shows a  
list of several ceramic capacitor manufacturers.  
Table 8 shows several inductors that work well with the  
LTC3576/LTC3576-1’s general purpose regulators. These  
inductors offer a good compromise in current rating, DCR  
and physical size. Consult each manufacturer for detailed  
information on their entire selection of inductors.  
Table 8. Recommended Inductors  
MAX MAX  
INDUCTOR  
TYPE  
L
I
DCR  
(Ω)  
SIZE IN mm  
(L × W × H) MANUFACTURER  
DC  
Table 9. Recommended Ceramic Capacitor Manufacturers  
(μH) (A)  
AVX  
www.avxcorp.com  
www.murata.com  
www.t-yuden.com  
www.vishay.com  
www.tdk.com  
DE2818C  
4.7 1.25 0.072  
3.3 1.45 0.053  
4.7 0.79 0.24  
3.3 0.90 0.20  
2.2 1.14 0.14  
Toko  
www.toko.comm  
3.0 × 2.8 × 1.8  
3.0 × 2.8 × 1.8  
3.6 × 3.6 × 1.2  
3.6 × 3.6 × 1.2  
3.6 × 3.6 × 1.2  
3.0 × 2.8 × 1.2  
3.0 × 2.8 × 1.2  
3.0 × 2.8 × 1.2  
Murata  
D312C  
Taiyo Yuden  
Vishay Siliconix  
TDK  
DE2812C  
4.7  
3.3  
2.0  
1.2 1.13*  
1.4 0.10*  
1.8 0.067*  
Overvoltage Protection  
CDRH3D16  
CDRH2D11  
4.7  
3.3  
2.2  
4.7  
3.3  
0.9  
0.11  
Sumida  
4.0 × 4.0 × 1.8  
4.0 × 4.0 × 1.8  
4.0 × 4.0 × 1.8  
3.2 × 3.2 × 1.2  
3.2 × 3.2 × 1.2  
3.2 × 3.2 × 1.2  
4.9 × 4.9 × 1.0  
3.1 × 3.1 × 1.8  
3.1 × 3.1 × 1.8  
3.1 × 3.1 × 1.8  
3.1 × 3.1 × 1.2  
3.1 × 3.1 × 1.2  
3.1 × 3.1 × 1.2  
5.2 × 5.2 × 1.2  
5.2 × 5.2 × 1.2  
5.2 × 5.2 × 1.2  
5.2 × 5.2 × 1.0  
5.2 × 5.2 × 1.0  
5.2 × 5.2 × 1.0  
1.1 0.085  
1.2 0.072  
www.sumida.com  
V
BUS  
can be protected from overvoltage damage with two  
additional components, a resistor R1 and an N-channel  
MOSFET MN1, as shown in Figure 6. Suitable choices for  
MN1 are listed in Table 10.  
0.5  
0.6 0.123  
2.2 0.78 0.098  
4.7 0.75 0.19  
0.17  
CLS4D09  
SD3118  
4.7  
1.3 0.162  
Cooper  
www.cooperet.com  
Table 10. Recommended N-channel MOSFETs for the  
Overvoltage Protection Circuit  
3.3 1.59 0.113  
2.2  
4.7  
2.0 0.074  
0.8 0.246  
PART NUMBER  
Si1472DH  
BVDSS  
30V  
R
PACKAGE  
SC70-6  
SOT-23  
SOT-23  
SOT-23  
SOT-23  
SOT-23  
WDFN6  
ON  
SD3112  
SD12  
3.3 0.97 0.165  
2.2 1.12 0.14  
4.7 1.29 0.117*  
3.3 1.42 0.104*  
2.2 1.80 0.075*  
4.7 1.08 0.153*  
3.3 1.31 0.108*  
2.2 1.65 0.091*  
82mΩ  
60mΩ  
65mΩ  
80mΩ  
35mΩ  
50mꢀ  
35mΩ  
Si2302ADS  
Si2306BDS  
Si2316BDS  
IRLML2502  
FDN372S  
20V  
30V  
30V  
SD10  
20V  
30V  
LPS3015  
4.7  
3.3  
2.2  
1.1  
1.3  
1.5  
0.2  
0.13  
0.11  
Coilcraft  
www.coilcraft.com  
3.0 × 3.0 × 1.5  
3.0 × 3.0 × 1.5  
3.0 × 3.0 × 1.5  
NTLJS4114N  
30V  
R1 is a 6.2k resistor and must be rated for the power dis-  
sipated during maximum overvoltage. In an overvoltage  
condition the OVSENS pin will be clamped at 6V. R1 must  
be sized appropriately to dissipate the resultant power.  
For example, a 1/10W 6.2k resistor can have at most  
*Typical DCR  
Step-Down Switching Regulator Input/Output Bypass  
Capacitor Selection  
Low ESR (equivalent series resistance) MLCCs should  
be used at each switching regulator output as well as at  
√P  
• 6.2kꢀ = 25V applied across its terminals. With  
MAX  
the 6V at OVSENS, the maximum overvoltage magnitude  
thatthisresistorcanwithstandis31V.A1/4W6.2kresistor  
raises this value to 45V. OVSENS’s absolute maximum  
current rating of 10mA imposes an upper limit of 68V  
each switching regulator input supply (V ). Only X5R  
INx  
or X7R ceramic capacitors should be used because they  
retaintheircapacitanceoverwidervoltageandtemperature  
ranges than other ceramic types. A 10ꢁF output capaci-  
protection.  
3576fb  
35  
LTC3576/LTC3576-1  
APPLICATIONS INFORMATION  
MP1  
MN1  
USB/WALL  
ADAPTER  
V
BUS  
D1  
C1  
MN1  
USB/WALL  
ADAPTER  
V
LTC3576/  
BUS  
LTC3576-1  
C1  
LTC3576/  
R1  
R2  
LTC3576-1  
OVGATE  
OVSENS  
R1  
OVGATE  
OVSENS  
3576 F08  
V
BUS  
V
BUS  
POSITIVE PROTECTION UP TO BVDSS OF MN1  
NEGATIVE PROTECTION UP TO BVDSS OF MP1  
3576 F06  
Figure 6. Overvoltage Protection  
Figure 8. Dual Polarity Voltage Protection  
transforms the voltage at V  
to a voltage just above  
BUS  
M1  
V1  
V2  
WALL  
the level at BAT, while limiting power to less than the  
amount programmed at CLPROG. The charger should be  
programmed (with the PROG pin) to deliver the maximum  
safe charging current without regard to the USB specifi-  
cations. If there is insufficient current available to charge  
the battery at the programmed rate, it will reduce charge  
OVGATE  
LTC3576/  
LTC3576-1  
BUS  
V
M2  
D2  
D1  
C1  
GND  
R1  
OVSENS  
current until the system load on V  
is satisfied and the  
OUT  
3576 F07  
V
current limit is satisfied. Programming the charger  
BUS  
for more current than is available will not cause the aver-  
age input current limit to be violated. It will merely allow  
the battery charger to make use of all available power to  
chargethebatteryasquicklyaspossible,andwithminimal  
dissipation within the charger.  
Figure 7. Dual-Input Overvoltage Protection  
I
t is possible to protect both VBUS and WALL from  
overvoltage damage with several additional components,  
as shown in Figure 7. Schottky diodes D1 and D2 pass the  
larger of V1 and V2 to R1 and OVSENS. If either V1 or V2  
exceeds 6V plus VF (Schottky), OVGATE will be pulled to  
GNDandboththeWALLandUSBinputswillbeprotected.  
Eachinputisprotecteduptothedrain-sourcebreakdown,  
BVDSS, of MN1 and MN2. R1 must also be rated for the  
power dissipated during maximum overvoltage.  
Battery Charger Stability Considerations  
TheLTC3576/LTC3576-1’sbatterychargercontainsbotha  
constant-voltage and a constant-current control loop. The  
constant-voltage loop is stable without any compensation  
when a battery is connected with low impedance leads.  
Excessive lead length, however, may add enough series  
inductance to require a bypass capacitor of at least 1μF  
from BAT to GND.  
Reverse Voltage Protection  
The LTC3576/LTC3576-1 can also be easily protected  
against the application of reverse voltages, as shown in  
Figure 8. D1 and R1 are necessary to limit the maximum  
High value, low ESR MLCCs reduce the constant-voltage  
loop phase margin, possibly resulting in instability. Up  
to 22μF may be used in parallel with a battery, but larger  
capacitors should be decoupled with 0.2Ω to 1Ω of series  
resistance.  
V
seenbyMP1duringpositiveovervoltageevents.D1’s  
GS  
breakdownvoltagemustbesafelybelowMP1’sBVGS.The  
circuit shown in Figure 8 offers forward voltage protection  
up to MN1’s BVDSS and reverse voltage protection up to  
MP1’s BVDSS.  
Furthermore, a 100μF MLCC in series with a 0.3Ω resistor  
from BAT to GND is required to prevent oscillation when  
the battery is disconnected.  
Battery Charger Over Programming  
The USB high power specification allows for up to 2.5W  
to be drawn from the USB port. The LTC3576/LTC3576-1’s  
bidirectional switching regulator in step-down mode  
In constant-current mode, the PROG pin is in the feed-  
back loop rather than the battery voltage. Because of the  
additional pole created by any PROG pin capacitance,  
3576fb  
36  
LTC3576/LTC3576-1  
APPLICATIONS INFORMATION  
capacitance on this pin must be kept to a minimum. With  
no additional capacitance on the PROG pin, the charger  
is stable with program resistor values as high as 25k.  
However, additional capacitance on this node reduces the  
maximumallowedprogramresistor.Thepolefrequencyat  
the PROG pin should be kept above 100kHz. Therefore, if  
of the thermistor. Using the bias resistor in addition to an  
adjustmentresistor,boththeupperandthelowertempera-  
ture trip points can be independently programmed with  
the constraint that the difference between the upper and  
lower temperature thresholds cannot decrease. Examples  
of each technique are given below.  
the PROG pin has a parasitic capacitance, C  
, the fol-  
PROG  
NTC thermistors have temperature characteristics which  
areindicatedonresistance-temperatureconversiontables.  
TheVishay-DalethermistorNTHS0603N011-N1003F,used  
in the following examples, has a nominal value of 100k  
and follows the Vishay Curve 1 resistance-temperature  
characteristic.  
lowing equation should be used to calculate the maximum  
resistance value for R  
:
PROG  
1
RPROG  
2π • 100kHz • CPROG  
In the explanation below, the following notation is used.  
R25 = Value of the Thermistor at 25°C  
Alternate NTC Thermistors and Biasing  
The LTC3576/LTC3576-1 provide temperature qualified  
charging if a grounded thermistor and a bias resistor  
are connected to NTC. By using a bias resistor whose  
value is equal to the room temperature resistance of the  
thermistor (R25) the upper and lower temperatures are  
pre-programmed to approximately 40°C and 0°C respec-  
tively assuming a Vishay Curve 1 thermistor.  
R
R
= Value of thermistor at the cold trip point  
= Value of the thermistor at the hot trip  
NTC|COLD  
NTC|HOT  
point  
r
r
= Ratio of R  
to R25  
COLD  
NTC|COLD  
= Ratio of R  
to R25  
HOT  
NTC|HOT  
The upper and lower temperature thresholds can be ad-  
justed by either a modification of the bias resistor value  
or by adding a second adjustment resistor to the circuit.  
If only the bias resistor is adjusted, then either the upper  
or the lower threshold can be modified but not both. The  
other trip point will be determined by the characteristics  
R
– Primary thermistor bias resistor  
NOM  
(see Figure 9)  
R1 = Optional temperature range adjustment resistor  
(see Figure 10)  
LTC3576/LTC3576-1  
NTC BLOCK  
NTCBIAS  
LTC3576/LTC3576-1  
NTC BLOCK  
NTCBIAS  
3
4
3
0.765 • NTCBIAS  
R
0.765 • NTCBIAS  
NOM  
+
R
NOM  
100k  
105k  
+
TOO_COLD  
TOO_HOT  
TOO_COLD  
TOO_HOT  
NTC  
NTC  
4
R1  
12.7k  
R
NTC  
100k  
T
+
+
R
NTC  
100k  
T
0.349 • NTCBIAS  
0.349 • NTCBIAS  
+
+
NTC_ENABLE  
NTC_ENABLE  
0.1V  
0.1V  
3576 F10  
3576 F09  
Figure 9. Standard NTC Configuration  
Figure 10. Modified NTC Configuration  
3576fb  
37  
LTC3576/LTC3576-1  
APPLICATIONS INFORMATION  
The trip points for the LTC3576/LTC3576-1’s temperature  
qualificationareinternallyprogrammedat0.349NTCBIAS  
for the hot threshold and 0.765NTCBIAS for the cold  
threshold.  
From the Vishay Curve 1 R-T characteristics, r  
is  
HOT  
0.2488 at 60°C. Using the above equation, R  
should  
NOM  
be set to 46.4k. With this value of R  
, r  
is 1.436  
NOM COLD  
and the cold trip point is about 16°C. Notice that the span  
is now 44°C rather than the previous 40°C. This is due to  
the decrease in “temperature gain” of the thermistor as  
absolute temperature increases.  
Therefore, the hot trip point is set when:  
RNTC HOT  
NTCBIAS= 0.349 NTCBIAS  
RNOM +RNTC HOT  
The upper and lower temperature trip points can be inde-  
pendentlyprogrammedbyusinganadditionalbiasresistor  
asshowninFigure10. Thefollowingformulascanbeused  
And the cold trip point is set when:  
to compute the values of R  
and R1:  
NOM  
RNTC COLD  
NTCBIAS= 0.765NTCBIAS  
RNOM +RNTC COLD  
rCOLD rHOT  
RNOM  
=
R25  
2.714  
R1= 0.536 RNOM rHOT R25  
Solving these equations for R  
results in the following:  
and R  
NTC|HOT  
NTC|COLD  
For example, to set the trip points to 0°C and 45°C with  
a Vishay Curve 1 thermistor choose:  
R
= 0.536 • R  
NTC|HOT  
NOM  
and  
3.266 – 0.4368  
RNOM  
=
100k =104.2k  
R
= 3.25 • R  
2.714  
NTC|COLD  
NOM  
By setting R  
equal to R25, the above equations result  
NOM  
= 0.536 and r  
the nearest 1% value is 105k:  
in r  
= 3.25. Referencing these ratios  
HOT  
COLD  
R1 = 0.536 • 105k – 0.4368 • 100k = 12.6k  
to the Vishay Resistance-Temperature Curve 1 chart gives  
a hot trip point of about 40°C and a cold trip point of about  
0°C. The difference between the hot and cold trip points  
is approximately 40°C.  
the nearest 1% value is 12.7k. The final solution is shown  
in Figure 10 and results in an upper trip point of 45°C and  
a lower trip point of 0°C.  
By using a bias resistor, R  
, different in value from  
NOM  
Hot Plugging and USB Inrush Current Limiting  
R25, the hot and cold trip points can be moved in either  
direction. The temperature span will change somewhat  
due to the nonlinear behavior of the thermistor. The fol-  
lowing equations can be used to calculate a new value for  
the bias resistor:  
The overvoltage protection circuit provides inrush current  
limiting due to the long time it takes for OVGATE to fully  
enhancetheN-channelMOSFET. Thispreventsthecurrent  
from building up in the cable too quickly thus dampen-  
ing out any resonant overshoot on V . It is possible to  
BUS  
rHOT  
RNOM  
=
=
R25  
observe voltage overshoot on V  
when connecting the  
BUS  
0.536  
r
LTC3576/LTC3576-1toalabpowersupplyiftheovervoltage  
protection circuit is not used. This overshoot is caused by  
the inductance of the long leads from the power supply to  
RNOM  
COLD R25  
3.25  
V
. Twisting the wires together from the supply to V  
BUS  
BUS  
where r  
and r  
are the resistance ratios at the de-  
HOT  
COLD  
can greatly reduce the parasitic inductance of these long  
sired hot and cold trip points. Note that these equations  
are linked. Therefore, only one of the two trip points can  
be chosen, the other is determined by the default ratios  
designed in the IC. Consider an example where a 60°C  
hot trip point is desired.  
leadskeepingthevoltageatV tosafelevels.USBcables  
BUS  
are generally manufactured with the power leads in close  
proximity, and thus have fairly low parasitic inductance.  
3576fb  
38  
LTC3576/LTC3576-1  
APPLICATIONS INFORMATION  
Hot Plugging and USB On-the-Go  
For V  
pulsing, the limit on the V  
capacitance on  
BUS  
BUS  
the A device allows a B device to differentiate between  
a powered down on-the-go device and a powered down  
standardhost. TheBdevicewillsendoutapulseofcurrent  
If there is more than 4.3V on V  
when on-the-go is  
BUS  
enabled, the bidirectional switching regulator will not try  
to drive V . If USB on-the-go is enabled and an external  
BUS  
that will raise V  
to a voltage between 2.1V and 5.25V if  
BUS  
supply is then connected to V , one of three things will  
BUS  
connected to an on-the-go A device which must have no  
more than 6.5μF. An on-the-go A device must drive V  
happen depending on the properties of the external sup-  
ply. If the external supply has a regulation voltage higher  
than 5.1V, the bidirectional switching regulator will stop  
BUS  
as soon as the current pulse raises V  
above 2.1V if the  
BUS  
device is capable of responding to V  
pulsing.  
BUS  
switching and V  
will be held at the regulation voltage  
BUS  
of the external supply. If the external supply has a lower  
This same current pulse must not raise V  
any higher  
BUS  
regulation voltage and is capable of only sourcing current  
than 2V when connected to a standard host which must  
haveatleast9F. The9Fforastandardhostrepresents  
then V  
will be regulated to 5.1V. The external supply  
BUS  
will not source current to V  
.
the minimum capacitance with V  
between 4.75V and  
BUS  
BUS  
5.25V. Since the SRP pulse must not drive V  
greater  
BUS  
For a supply that can also sink current and has a regula-  
tion voltage less than 5.1V, the bidirectional switching  
regulator will source current into the external supply in an  
than2V, thecapacitanceseenatthesevoltagelevelscanbe  
greaterthan9F,especiallyifMLCCsareused.Therefore,  
the 96μF represents a lower bound on the standard host  
bypass capacitance for determining the amplitude and  
duration of the current pulse. More capacitance will only  
attempt to bring V  
up to 5.1V. As long as the external  
BUS  
supply holds V  
to more than 4V or V  
+ 70mV, the  
BUS  
OUT  
bidirectional switching regulator will source up to 680mA  
into the supply. If V is held to a voltage that is less than  
decrease the maximum level that V  
given current pulse.  
will rise to for a  
BUS  
BUS  
4V and V  
+ 70mV then the short circuit timer will shut  
OUT  
off the switching regulator after 7.2ms. The CHRG pin will  
Figure 11 shows an on-the-go device using the LTC3576/  
LTC3576-1 acting as the A device. Additional capacitance  
then blink indicating a short circuit current fault.  
can be placed on the V  
pin of the LTC3576/LTC3576-1  
BUS  
V
Bypass Capacitance and USB On-The-Go  
when using the overvoltage protection circuit. A B device  
may not be able to distinguish between a powered down  
LTC3576/LTC3576-1 with overvoltage protection and a  
powered down standard host because of this extra ca-  
BUS  
Session Request Protocol  
Whentwoon-the-godevicesareconnected,onewillbethe  
A device and the other will be the B device depending on  
whether the device is connected to a micro A or micro B  
plug. The A device provides power to the B device and  
starts as the host. To prolong battery life, the A device can  
pacitance. In addition, if the SRP pulse raises V  
above  
BUS  
its UVLO threshold of 4.3V the LTC3576/LTC3576-1 will  
assume input power is available and will not attempt to  
drive V . Therefore, it is recommended that an on-  
BUS  
power down V  
when the bus is not being used. If the A  
BUS  
the-go device using the LTC3576/LTC3576-1 respond to  
device has powered down V , the B device can request  
BUS  
data-line pulsing.  
the A device to power up V  
and start a new session us-  
BUS  
ing the session request protocol (SRP). The SRP consists  
of data-line pulsing and V pulsing. The B device must  
When an on-the-go device using the LTC3576/LTC3576-1  
becomes the B device, as in Figure 12, it must send out  
BUS  
+
first pulse the D or D data line. The B device must then  
a data line pulse followed by a V  
pulse to request a  
BUS  
pulse V only if the A device does not respond to the  
session from the A device. The on-the-go device designer  
can choose how much capacitance will be placed on the  
BUS  
data-linepulse. TheAdeviceisrequiredtorespondtoonly  
one of the pulsing methods. A devices that never power  
V
pin of the LTC3576/LTC3576-1 and then generate  
pulse that can distinguish between a powered  
BUS  
down V  
are not required to respond to the SRP.  
a V  
BUS  
BUS  
3576fb  
39  
LTC3576/LTC3576-1  
APPLICATIONS INFORMATION  
OVP  
(OPTIONAL)  
OVSENS  
ON-THE-GO  
POWER  
MANAGER  
OVGATE  
LTC3576/  
LTC3576-1  
V
BUS  
ENOTG  
C
A
C
B
<6.5μF  
<6.5μF  
WITHOUT OVP  
+
D
D
ON-THE-GO  
TRANSCEIVER  
ON-THE-GO  
TRANSCEIVER  
3576 F11  
A DEVICE  
B DEVICE  
Figure 11. LTC3576/LTC3576-1 as the A Device  
OVP  
(OPTIONAL)  
OVSENS  
STANDARD  
USB HOST OR  
ON-THE-GO  
POWER  
OVGATE  
LTC3576/  
LTC3576-1  
V
BUS  
MANAGER  
ENOTG  
C
C
A
B
<6.5μF FOR OTG DEVICES  
<6.5μF  
>96μF FOR STANDARD HOST  
WITHOUT OVP  
STANDARD OR  
ON-THE-GO  
TRANSCEIVER  
D
ON-THE-GO  
TRANSCEIVER  
+
D
3576 F12  
B DEVICE  
A DEVICE  
Figure 12. LTC3576/LTC3576-1 as the B Device  
down on-the-go A device and a powered down standard  
host. A suitable pulse can be generated because of the  
disparity in the bypass capacitances of an on-the-go A  
device and a standard host even if there is somewhat  
high frequency components. High frequency currents,  
such as the V , V , V and V currents tend to find  
BUS IN1 IN2  
IN3  
their way on the ground plane along a mirror path directly  
beneath the incident path on the top of the board. If there  
are slits or cuts in the ground plane due to other traces  
on that layer, the current will be forced to go around the  
slits. If high frequency currents are not allowed to flow  
back through their natural least-area path, excessive  
voltage will build up and radiated emissions will occur  
(see Figure 13). There should be a group of vias directly  
under the grounded backside leading directly down to an  
internal ground plane. To minimize parasitic inductance,  
the ground plane should be as close as possible to the  
top plane of the PC board (layer 2).  
more than 6.5μF capacitance connected to the V  
of the LTC3576/LTC3576-1.  
pin  
BUS  
Board Layout Considerations  
The Exposed Pad on the backside of the LTC3576/  
LTC3576-1 package must be securely soldered to the PC  
board ground. This is the primary ground pin in the pack-  
age, and it serves as the return path for both the control  
circuitry and the N-channel MOSFET switches.  
Furthermore, duetoitshighfrequencyswitchingcircuitry,  
it is imperative that the input capacitor, inductor, and  
output capacitor be as close to the LTC3576/LTC3576-1  
as possible and that there be an unbroken ground plane  
under the LTC3576/LTC3576-1 and all of their external  
The IDGATE pin for the external ideal diode controller has  
extremely limited drive current. Care must be taken to  
minimize leakage to adjacent PC board traces. 100nA of  
leakage from this pin will introduce an additional offset to  
3576fb  
40  
LTC3576/LTC3576-1  
APPLICATIONS INFORMATION  
3576 F13  
Figure 13. Higher Frequency Ground Current Follow Their  
Incident Path. Slices in the Ground Plane Create Large Loop  
Areas. The Large Loop Areas Increase the Inductance of the  
Path Leading to Higher System Noise  
theidealdiodeofapproximately10mV.Tominimizeleakage,  
the trace can be guarded on the PC board by surrounding  
as possible. Use area fills whenever possible. This  
also applies to the PowerPath switching regulator  
it with V  
connected metal, which should generally be  
inductor and the output capacitor on V . The GND  
OUT  
OUT  
less than one volt higher than IDGATE.  
side of the output capacitors should connect directly  
to the thermal ground plane of the part.  
When laying out the printed circuit board, the following  
checklist should be used to ensure proper operation of  
the LTC3576/LTC3576-1:  
4. The switching power traces connecting SW, SW1,  
SW2, SW3 and the switch node of the external step-  
down switching regulator to their respective induc-  
tors should be minimized to reduce radiated EMI and  
parasitic coupling. Due to the large voltage swing  
of the switching nodes, sensitive nodes such as the  
feedback nodes (FB1, FB2 and FB3) should be kept  
far away or shielded from the switching nodes or  
poor performance could result.  
1. The Exposed Pad of the package (Pin 39) should  
connect directly to a large ground plane to minimize  
thermal and electrical impedance.  
2. The traces connecting V , V , V , V and  
BUS IN1 IN2 IN3  
V of the external step-down switching regulator  
IN  
to their respective decoupling capacitors should be  
as short as possible. The GND side of these capaci-  
tors should connect directly to the ground plane of  
the part. These capacitors provide the AC current to  
the internal power MOSFETs and their drivers. It is  
critical to minimize inductance from these capacitors  
to the LTC3576/LTC3576-1 and external step-down  
switching regulator.  
5. Keep the feedback pin traces (FB1, FB2, FB3 and FB  
of the external step-down switching regulator) as  
short as possible. Minimize any parasitic capacitance  
between the feedback traces and any switching node  
(i.e., SW, SW1, SW2, SW3 and logic signals). If nec-  
essary shield the feedback nodes with a GND trace  
6. Connect V , V and V to V through a short  
OUT  
IN1 IN2  
low impedance trace.  
IN3  
3. Connections between the step-down switching regu-  
lator (both internal and external) inductors and their  
respective output capacitors should be kept as short  
3576fb  
41  
LTC3576/LTC3576-1  
TYPICAL APPLICATIONS  
Minimum Parts Count USB Power Manager with Low-Battery Start-Up and USB On-the-Go  
USB  
26  
27  
28  
L1  
ON-THE-GO  
3.3μH  
V
WALL ACPR  
C
35  
34  
36  
33  
31  
32  
TO OTHER  
LOADS  
USB,  
WALL ADAPTER  
V
V
SW  
OUT  
BUS  
BUS  
C1  
10μF  
0805  
V
C3  
22μF  
0805  
5
6
3
OVGATE  
IDGATE  
BAT  
OVSENS  
NTCBIAS  
+
Li-Ion  
4
29  
1
NTC  
8
9
7
PROG  
CLPROG  
V
IN1  
L2  
4.7μH  
1.76V TO 3.3V  
400mA  
C2  
0.1μF  
0402  
MEMORY  
SW1  
FB1  
1k  
3.01k  
1.02M  
324k  
10pF  
10pF  
10pF  
1μF  
10μF  
10μF  
10μF  
LTC3576/LTC3576-1  
LDO3V3  
2
24  
23  
25  
V
IN2  
12  
L3  
1.61V TO 3.03V  
400mA  
1μF  
DV  
CC  
4.7μH  
I/O  
SW2  
FB2  
1μF  
1.02M  
365k  
30  
PUSHBUTTON  
MICROCONTROLLER  
CHRG  
MICROPROCESSOR  
13, 14  
16  
17  
20  
2
I C  
V
IN3  
L4  
2μH  
0.8V TO 1.51V  
1A  
10  
22  
CORE  
POR  
SW3  
FB3  
EN1  
751k  
806k  
1μF  
EN2  
C1: MURATA GRM21BR7A106KE51L  
C3: TAIYO YUDEN JMK212BJ226MG  
L1: COILCRAFT LPS4018-332LM  
L2, L3: TOKO 1098AS-4R7M  
19  
11  
37  
38  
EN3  
10k  
ENOTG  
L4: TOKO 1098AS-2R0M  
I
I
LIM0  
LIM1  
21  
3576 TA02  
RST3  
3576fb  
42  
LTC3576/LTC3576-1  
TYPICAL APPLICATIONS  
High Efficiency USB/Automotive Power Manager with Overvoltage Protection,  
Reverse-Voltage Protection, Low-Battery Start-Up and USB On-the-Go  
AUTOMOTIVE  
FIREWIRE, ETC.  
2
M1  
4
L1  
V
BOOST  
SW  
IN  
6.8μH  
0.47μF  
D1  
3
150k  
4.7μF  
68nF  
5
LT3480  
RUN/SS  
22μF  
499k  
100k  
40.2k  
8
10  
R
FB  
T
PG  
V
GND BD SYNC  
C
7
11  
1
6
9
M4  
USB  
26  
27  
28  
L2  
ON-THE-GO  
3.3μH  
V
WALL ACPR  
USB,  
WALL  
ADAPTER  
C
M3  
35  
34  
36  
33  
31  
32  
TO OTHER  
LOADS  
V
V
SW  
OUT  
BUS  
BUS  
M2  
C1  
22μF  
0805  
V
C3  
22μF  
0805  
2.2k  
IDGATE  
BAT  
M5  
5
6
R1  
6.2k  
OVGATE  
OVSENS  
+
Li-Ion  
30  
8
3
CHRG  
NTCBIAS  
100k  
R2  
V
IN1  
4
29  
1
L3  
4.7μH  
1.76V TO 3.3V  
400mA  
NTC  
9
7
PROG  
CLPROG  
MEMORY  
SW1  
FB1  
T
1.02M  
324k  
10pF  
1μF  
C2  
0.1μF  
0402  
100k  
1k  
3.01k  
10μF  
LTC3576/LTC3576-1  
LDO3V3  
2
24  
23  
25  
V
IN2  
12  
L4  
4.7μH  
1.61V TO 3.03V  
400mA  
1μF  
DV  
CC  
I/O  
SW2  
FB2  
1μF  
1.02M  
365k  
10pF  
PUSHBUTTON  
MICROCONTROLLER  
10μF  
MICROPROCESSOR  
13, 14  
16  
17  
20  
2
I C  
V
IN3  
L5  
2μH  
0.8V TO 1.51V  
1A  
10  
22  
CORE  
POR  
SW3  
FB3  
EN1  
751k  
806k  
10pF  
1μF  
EN2  
19  
11  
37  
38  
10μF  
EN3  
10k  
ENOTG  
I
I
LIM0  
LIM1  
21  
3576 TA03  
RST3  
C1, C3: TAYIO YUDEN JMK212BJ226MG L5: TOKO 1098AS-2R0M  
D1: DIODES INC. DFLS240L  
M1,M2,M4, M5: SILICONIX Si2333DS  
L1: TAIYO YUDEN NP06DZB6R8M  
L2: COILCRAFT LPS4018-332LM  
L3, L4: TOKO 1098AS-4R7M  
M3: ON SEMICONDUCTOR NTLJS4114N  
R1: 1/10W RESISTOR  
R2: CURVE 1  
3576fb  
43  
LTC3576/LTC3576-1  
TYPICAL APPLICATIONS  
High Efficiency USB/Automotive Power Manager with Overvoltage Protection, USB On-the-Go, Pushbutton Start,  
Automatic Supply Sequencing and 10 Second Push-and-Hold Hard Shutdown  
AUTOMOTIVE  
FIREWIRE, ETC.  
2
3
4
L1  
V
BOOST  
SW  
IN  
6.8μH  
0.47μF  
D1  
4.7μF  
150k  
68nF  
5
LT3480  
499k  
RUN/SS  
22μF  
100k  
40.2k  
8
10  
R
FB  
T
PG  
V
GND BD SYNC  
C
7
11  
1
6
9
M2  
USB  
26  
27  
28  
L2  
ON-THE-GO  
3.3μH  
V
WALL ACPR  
USB,  
WALL  
ADAPTER  
C
M1  
35  
34  
36  
33  
31  
32  
TO OTHER  
LOADS  
V
V
SW  
OUT  
BUS  
BUS  
C1  
22μF  
0805  
V
C3  
22μF  
0805  
2.2k  
IDGATE  
BAT  
M3  
5
6
R1  
6.2k  
OVGATE  
OVSENS  
+
Li-Ion  
30  
8
3
CHRG  
NTCBIAS  
100k  
V
IN1  
4
29  
1
1.76V TO 3.3V  
400mA  
NTC  
9
7
PROG  
CLPROG  
MEMORY  
SW1  
FB1  
L3  
4.7μH  
R2  
100k  
T
1.02M  
324k  
10pF  
1μF  
C2  
0.1μF  
0402  
1k  
3.01k  
10μF  
LTC3576/LTC3576-1  
14  
13  
12  
16  
22  
17  
SDA  
SCL  
V
IN3  
0.8V TO 1.51V  
1A  
EN2  
CORE  
POR  
DV  
SW3  
CC  
L5  
2μH  
1μF  
751k  
806k  
10pF  
1μF  
10k  
20  
FB3  
10μF  
2
LDO3V3  
1k  
1μF  
21  
24  
10  
23  
RST3  
V
IN2  
1.61V TO 3.03V  
400mA  
EN1  
1M  
I/O  
SW2  
4.7k  
EN3  
M4  
L4  
4.7μH  
1.02M  
365k  
10pF  
1μF  
5.1k 5.1k  
25  
11  
37  
38  
FB2  
10μF  
10μF  
ENOTG  
SDA  
SCL  
10k  
10μF  
I
I
LIM0  
LIM1  
2
SEND I C CODE: “0s1201F8”  
3576 TA04  
C1, C3: TAYIO YUDEN JMK212BJ226MG M1: ON SEMICONDUCTOR NTLJS4114N  
D1: DIODES INC. DFLS240L  
L1: TAIYO YUDEN NP06DZB6R8M  
L2: COILCRAFT LPS4018-332LM  
L3, L4: TOKO 1098AS-4R7M  
L5: TOKO 1098AS-2R0M  
M2, M3: SILICONIX Si2333DS  
M4: 2N7002  
R1: 1/10W RESISTOR  
R2: CURVE 1  
3576fb  
44  
LTC3576/LTC3576-1  
TYPICAL APPLICATIONS  
High Efficiency USB/Automotive Power Manager with Current Limiting and  
Overvoltage Protection on Both Inputs, Low-Battery Start-Up and USB On-the-Go  
AUTOMOTIVE  
FIREWIRE, ETC.  
7.5V TO 36V  
TRANSIENTS TO 60V  
7
8
1
3
L1  
4.7μH  
V
BOOST  
SW  
IN  
0.47μF  
D1  
4.7μF  
34.2k  
LT3653  
22μF  
6
5
I
I
SENSE  
LIM  
V
OUT  
V
V
GND HVOK  
C
9
2
4
USB  
26  
28  
27  
L2  
ON-THE-GO  
3.3μH  
ACPR WALL  
USB,  
C
M1  
35  
34  
36  
33  
31  
32  
TO OTHER  
LOADS  
WALL  
V
V
SW  
OUT  
BUS  
C1  
22μF  
0805  
ADAPTER  
V
BUS  
C3  
22μF  
0805  
IDGATE  
BAT  
5
6
R1  
6.2k  
OVGATE  
OVSENS  
+
Li-Ion  
3
NTCBIAS  
8
9
7
100k  
R2  
V
IN1  
4
29  
1
L3  
1.76V TO 3.3V  
400mA  
NTC  
4.7μH  
PROG  
CLPROG  
MEMORY  
SW1  
FB1  
T
1.02M  
10pF  
1μF  
C2  
0.1μF  
0402  
100k  
1k  
3.01k  
10μF  
10μF  
10μF  
324k  
LTC3576/LTC3576-1  
LDO3V3  
2
24  
23  
25  
V
IN2  
12  
L4  
4.7μH  
1.61V TO 3.03V  
400mA  
1μF  
DV  
CC  
I/O  
SW2  
FB2  
1μF  
1.02M  
365k  
10pF  
30  
PUSHBUTTON  
MICROCONTROLLER  
CHRG  
MICROPROCESSOR  
13, 14  
16  
17  
20  
2
I C  
V
IN3  
L5  
2μH  
0.8V TO 1.51V  
1A  
10  
22  
CORE  
POR  
SW3  
FB3  
EN1  
751k  
806k  
10pF  
1μF  
EN2  
19  
11  
37  
38  
EN3  
10k  
ENOTG  
I
I
LIM0  
LIM1  
21  
3576 TA05  
RST3  
C1, C3: TAYIO YUDEN JMK212BJ226MG M1: FAIRCHILD FDN327S  
D1: DIODES INC. DFLS140  
R1: 1/10W RESISTOR  
R2: CURVE 1  
L1: COILCRAFT MSS6132-472MLC  
L2: COILCRAFT LPS4018-332LM  
L3, L4: TOKO 1098AS-4R7M  
L5: TOKO 1098AS-2R0M  
3576fb  
45  
LTC3576/LTC3576-1  
TYPICAL APPLICATIONS  
High Efficiency USB/Wall Power Manager with Dual Overvoltage Protection,  
Reverse-Voltage Protection, Low-Battery Start-Up and USB On-The-Go  
5V WALL  
ADAPTER  
M3  
M4  
M1  
M2  
C1  
22μF  
0805  
M5  
USB  
5
27  
28  
L1  
ON-THE-GO  
3.3μH  
OVGATE WALL ACPR  
35  
34  
26  
36  
33  
31  
32  
TO OTHER  
LOADS  
USB  
V
V
V
SW  
BUS  
C2  
V
BUS  
C
OUT  
22μF  
C4  
22μF  
0805  
0805  
2.2k  
IDGATE  
BAT  
M6  
R1  
6.2k  
+
6
3
OVSENS  
NTCBIAS  
Li-Ion  
30  
8
CHRG  
100k  
R2  
V
IN1  
4
29  
1
L2  
4.7μH  
1.76V TO 3.3V  
400mA  
NTC  
9
7
PROG  
CLPROG  
MEMORY  
SW1  
FB1  
T
1.02M  
324k  
10pF  
1μF  
C3  
100k  
1k  
0.1μF  
0402  
3.01k  
10μF  
LTC3576/LTC3576-1  
LDO3V3  
2
24  
23  
25  
V
IN2  
12  
L3  
4.7μH  
1.61V TO 3.03V  
400mA  
1μF  
DV  
CC  
I/O  
SW2  
FB2  
1μF  
1.02M  
365k  
10pF  
PUSHBUTTON  
MICROCONTROLLER  
10μF  
MICROPROCESSOR  
13, 14  
16  
17  
20  
2
I C  
V
IN3  
L4  
2μH  
0.8V TO 1.51V  
1A  
10  
22  
CORE  
POR  
SW3  
FB3  
EN1  
751k  
806k  
10pF  
1μF  
EN2  
19  
11  
37  
38  
10μF  
EN3  
10k  
ENOTG  
I
I
LIM0  
LIM1  
21  
3576 TA07  
RST3  
C1, C2, C4: TAYIO YUDEN JMK212BJ226MG M1, M2, M5, M6: SILICONIX Si2333DS  
L1: COILCRAFT LPS4018-332LM  
L2, L3: TOKO 1098AS-4R7M  
L4: TOKO 1098AS-2R0M  
M3, M4: FAIRCHILD FDN327S  
R1: 1/10W RESISTOR  
R2: CURVE 1  
3576fb  
46  
LTC3576/LTC3576-1  
PACKAGE DESCRIPTION  
UFE Package  
38-Lead Plastic QFN (4mm × 6mm)  
(Reference LTC DWG # 05-08-1750 Rev B)  
0.70 p0.05  
4.50 p 0.05  
3.10 p 0.05  
2.40 REF  
2.65 p 0.05  
4.65 p 0.05  
PACKAGE OUTLINE  
0.20 p0.05  
0.40 BSC  
4.40 REF  
5.10 p 0.05  
6.50 p 0.05  
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS  
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED  
PIN 1 NOTCH  
R = 0.30 OR  
0.35 s 45o  
CHAMFER  
2.40 REF  
R = 0.10  
0.75 p 0.05  
TYP  
4.00 p 0.10  
37 38  
0.40 p 0.10  
PIN 1  
TOP MARK  
(NOTE 6)  
1
2
4.65 p 0.10  
4.40 REF  
6.00 p 0.10  
2.65 p 0.10  
(UFE38) QFN 0708 REV B  
0.200 REF  
R = 0.115  
TYP  
0.20 p 0.05  
0.40 BSC  
0.00 – 0.05  
BOTTOM VIEW—EXPOSED PAD  
NOTE:  
1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE  
2. DRAWING NOT TO SCALE  
3. ALL DIMENSIONS ARE IN MILLIMETERS  
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE  
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE  
5. EXPOSED PAD SHALL BE SOLDER PLATED  
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION  
ON THE TOP AND BOTTOM OF PACKAGE  
3576fb  
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.  
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-  
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.  
47  
LTC3576/LTC3576-1  
TYPICAL APPLICATION  
Firewire/Automotive Battery Charger with Automatic USB On-the-Go and Overvoltage Protection  
AUTOMOTIVE  
FIREWIRE, ETC.  
7.5V TO 36V  
TRANSIENTS TO 60V  
7
8
1
L1  
4.7μH  
V
IN  
BOOST  
SW  
0.47μF  
D1  
4.7μF  
LT3653  
22μF  
34.2k  
6
5
3
I
I
SENSE  
LIM  
V
OUT  
V
V
GND HVOK  
C
9
2
4
USB  
ON-THE-GO  
M1  
26  
28  
27  
J1  
L2  
MICRO-AB  
3.3μH  
ACPR WALL  
C
35  
34  
36  
33  
TO OTHER  
LOADS  
V
BUS  
V
V
SW  
BUS  
C1  
22μF  
0805  
D
V
BUS  
OUT  
C2  
22μF  
0805  
+
D
32  
5
6
ID  
OVGATE  
OVSENS  
BAT  
6.2k  
+
GND  
Li-Ion  
3.01k  
LTC3576/LTC3576-1  
TO USB  
TRANSCEIVER  
29  
1
2
LDO3V3  
PROG  
1μF  
CLPROG  
300k  
C3  
M2  
1k  
0.1μF  
0402  
11  
ENOTG  
3576 TA06  
V
BUS  
POWERS UP WHEN ID PIN HAS LESS THAN 10ꢀ TO GND (MICRO-A PLUG CONNECTED)  
C1, C2: TAIYO YUDEN JMK212BJ226MG L2: COILCRAFT LPS4018-332LM  
D1: DIODES INC. DFLS140  
J1: HIROSE ZX62-AB-5PA  
L1: COILCRAFT MSS6132-472MLC  
M1: FAIRCHILD FDN372S  
M2: SILICONIX Si2333DS  
RELATED PARTS  
PART NUMBER  
DESCRIPTION  
COMMENTS  
Power Management  
Switching USB Power Manager with Li-Ion/Polymer  
Chargers Plus Triple Buck DC/DC  
Maximizes Available Power from USB Port, Bat-Track, 1.5A Max Charge  
Current, 180mꢀ Ideal Diode with <50mꢀ Option, 3.3V/25mA Always-On  
LDO, Two 400mA and One 1A Buck Regulators, Instant-On Operation  
(LTC3555-1), Instant-On Operation and 4.1V Float Votlage (LTC3555-3),  
4mm × 5mm 28-Pin QFN Package  
LTC3555/LTC3555-1  
LTC3555-3  
Switching USB Power Manager with Li-Ion/Polymer  
Charger Plus Dual Buck Plus Buck-Boost DC/DC  
Maximizes Available Power from USB Port, Bat-Track, Instant-On  
Operation, 1.5A Max Charge Current, 180mꢀ Ideal Diode with <50mꢀ  
Option, 3.3V/25mA Always-On LDO, Two 400mA Buck Regulators,  
One 1A Buck-Boost Regulator, 4mm × 5mm 28-Pin QFN Package  
LTC3556  
LTC3586  
Switching USB Power Manager with Li-Ion/Polymer  
Charger Plus Dual Buck Plus Buck-Boost Plus Boost  
DC/DC  
Maximizes Available Power from USB Port, Bat-Track, Instant-On  
Operation, 1.5A Max Charge Current, 180mꢀ Ideal Diode with <50mꢀ  
Option, 3.3V/25mA Always-On LDO, Two 400mA Synchronous Buck  
Regulators, One 1A Buck-Boost Regulator, One 600mA Boost Regulator,  
4mm × 6mm 38-Pin QFN Package  
Switching USB Power Manager and Battery Chargers  
with Overvoltage Protection  
Maximizes Available Power from USB Port, Bat-Track, Instant-On  
Operation, 1.5A Max Charge Current, 180mꢀ Ideal Diode with <50mꢀ  
Option, Controller for External High Voltage Buck Regulator, Protection  
Against Transients of Up to 60V, 3.3V/25mA Always-On LDO,4.1V Float  
Voltage (LTC4098-1), 4mm × 3mm 14-Pin DFN Package  
LTC4098/LTC4098-1  
3576fb  
LT 0809 REV B • PRINTED IN USA  
LinearTechnology Corporation  
1630 McCarthy Blvd., Milpitas, CA 95035-7417  
48  
© LINEAR TECHNOLOGY CORPORATION 2008  
(408) 432-1900 FAX: (408) 434-0507 www.linear.com  

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