LTC3558EUD#PBF [Linear]
LTC3558 - Linear USB Battery Charger with Buck and Buck-Boost Regulators; Package: QFN; Pins: 20; Temperature Range: -40°C to 85°C;型号: | LTC3558EUD#PBF |
厂家: | Linear |
描述: | LTC3558 - Linear USB Battery Charger with Buck and Buck-Boost Regulators; Package: QFN; Pins: 20; Temperature Range: -40°C to 85°C 稳压器 电池 |
文件: | 总32页 (文件大小:398K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
LTC3558
Linear USB Battery Charger
with Buck and
Buck-Boost Regulators
FEATURES
DESCRIPTION
The LTC®3558 is a USB battery charger with dual high ef-
ficiency switching regulators. The device is ideally suited
to power single-cell Li-Ion/Polymer based handheld ap-
plications needing multiple supply rails.
Battery Charger
n
Standalone USB Charger
n
Up to 950mA Charge Current Programmable via
Single Resistor
n
HPWR Input Selects 20% or 100% of Programmed
Battery charge current is programmed via the PROG pin
and the HPWR pin with capability up to 950mA of current
at the BAT pin. The CHRG pin allows battery status to be
monitored continuously during the charging process. An
internal timer controls charger termination.
Charge Current
n
NTC Input for Temperature Qualified Charging
n
Internal Timer Termination
Bad Battery Detection
n
Switching Regulators (Buck and Buck-Boost)
Thepartincludesmonolithicsynchronousbuckandbuck-
boost regulators that can provide up to 400mA of output
current each and operate at efficiencies greater than 90%
over the entire Li-Ion/Polymer battery range. The buck-
boostregulatorcanregulateitsprogrammedoutputvoltage
at its rated deliverable current over the entire Li-Ion range
without drop out, increasing battery runtime.
n
Up to 400mA Output Current per Regulator
n
2.25MHz Constant-Frequency Operation
Power Saving Burst Mode® Operation
n
n
Low Profile, 20-Lead, 3mm × 3mm QFN Package
APPLICATIONS
TheLTC3558isofferedinalowprofile(0.75mm),thermally
enhanced, 20-lead (3mm × 3mm) QFN package.
, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology
Corporation. All other trademarks are the property of their respective owners.
n
SD/Flash-Based MP3 Players
Low Power Handheld Applications
n
TYPICAL APPLICATION
USB Charger Plus Buck Regulator and Buck-Boost Regulator
Demo Board
USB (4.3V TO 5.5V)
V
BAT
CC
SINGLE
Li-lon CELL
(2.7V TO 4.2V)
+
1μF
PV
IN1
IN2
PV
1.74k
PROG
NTC
10μF
1.2V AT 400mA
SW1
4.7μH
LTC3558
10pF
10μF
324k
649k
CHRG
SUSP
HPWR
MODE
EN1
FB1
SWAB2
2.2μH
3.3V AT 400mA
DIGITAL
CONTROL
SWCD2
V
OUT2
121k
22μF
324k
105k
33pF
EN2
FB2
15k
330pF
10pF
EXPOSED
PAD
GND
V
C2
3558 TA01
3558f
1
LTC3558
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
V
(Transient);
TOP VIEW
CC
t < 1ms and Duty Cycle < 1%....................... –0.3V to 7V
(Static) .................................................. –0.3V to 6V
V
CC
20 19 18 17 16
BAT, CHRG ................................................... –0.3V to 6V
EN2
15
14
13
12
11
GND
BAT
1
2
3
4
5
V
PROG, SUSP.................................–0.3V to (V + 0.3V)
C2
CC
FB2
21
8
MODE
FB1
HPWR, NTC...................–0.3V to Max (V , BAT) + 0.3V
CC
SUSP
PROG Pin Current...............................................1.25mA
V
EN1
OUT2
BAT Pin Current ..........................................................1A
6
7
9 10
PV , PV ..................................–0.3V to (BAT + 0.3V)
IN1
IN2
EN1, EN2, MODE, V
.............................. –0.3V to 6V
OUT2
UD PACKAGE
20-LEAD (3mm × 3mm) PLASTIC QFN
FB1, SW1......................... –0.3V to (PV + 0.3V) or 6V
IN1
FB2, V , SWAB2............. –0.3V to (PV + 0.3V) or 6V
C2
IN2
OUT2
T
= 125°C, θ = 68°C/W
JA
JMAX
SWCD2 ............................–0.3V to (V
+ 0.3V) or 6V
EXPOSED PAD (PIN 21) IS GND, MUST BE SOLDERED TO PCB
I
I
...............................................................600mA DC
SW1
, I
, I
...................................750mA DC
SWAB2 SWCD2 VOUT2
Junction Temperature (Note 2) ............................. 125°C
Operating Temperature Range (Note 3).... –40°C to 85°C
Storage Temperature.............................. –65°C to 125°C
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
20-Lead (3mm × 3mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 85°C
LTC3558EUD#PBF
LTC3558EUD#TRPBF
LDCD
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/
3558f
2
LTC3558
ELECTRICAL CHARACTERISTICS The l denotes specifications that apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. VCC = 5V, BAT = PVIN1 = PVIN2 = 3.6V, RPROG = 1.74k, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Battery Charger
l
V
Input Supply Voltage
4.3
5.5
V
CC
I
Battery Charger Quiescent Current
(Note 4)
Standby Mode, Charge Terminated
285
8.5
400
17
μA
μA
VCC
Suspend Mode, V
= 5V
SUSP
V
BAT Regulated Output Voltage
4.179
4.165
440
84
4.200
4.200
460
92
–3.5
–2.5
–1.5
4.221
4.235
500
100
–7
–4
–3
V
V
mA
mA
μA
μA
μA
FLOAT
CHG
0°C ≤ T ≤ 85°C
HPWR = 1
HPWR = 0
A
l
I
I
Constant-Current Mode Charge
Current
Battery Drain Current
Standby Mode, Charger Terminated, EN1 = EN2 = 0
Shutdown, V < V , BAT = 4.2V, EN1 = EN2 = 0
BAT
CC
UVLO
Suspend Mode, SUSP = 5V, BAT = 4.2V, EN1 = EN2 = 0
= 0V, EN1 = EN2 = 1, MODE = 1,
V
CC
FB1 = FB2 = 0.85V, V
= 3.6V
–50
4
–100
4.125
μA
V
OUT2
V
UVLO
Undervoltage Lockout Threshold
Undervoltage Lockout Hysteresis
BAT = 3.5V, V Rising
3.85
30
CC
BAT = 3.5V
200
50
mV
mV
ΔV
UVLO
V
Differential Undervoltage Lockout
Threshold
BAT = 4.05V, (V – BAT) Falling
70
DUVLO
CC
Differential Undervoltage Lockout
Hysteresis
BAT = 4.05V
130
mV
ΔV
DUVLO
V
PROG
PROG Pin Servo Voltage
HPWR = 1
HPWR = 0
1.000
0.200
0.100
V
V
V
BAT < V
TRKL
h
PROG
Ratio of I to PROG Pin Current
800
mA/mA
BAT
I
Trickle Charge Current
BAT < V
36
46
56
3
mA
TRKL
TRKL
V
Trickle Charge Threshold Voltage
Trickle Charge Hysteresis Voltage
Recharge Battery Threshold Voltage
Recharge Comparator Filter Time
Safety Timer Termination Period
Bad Battery Termination Time
BAT Rising
2.8
2.9
100
–95
1.7
4
V
TRKL
mV
ΔV
ΔV
TRKL
Threshold Voltage Relative to V
BAT Falling
–75
–115
mV
FLOAT
RECHRG
t
t
t
ms
RECHRG
BAT = V
3.5
0.4
4.5
0.6
Hour
Hour
mA/mA
ms
TERM
FLOAT
TRKL
BAT < V
0.5
0.1
2.2
500
BADBAT
h
End-of-Charge Indication Current Ratio (Note 5)
0.085
0.11
C/10
C/10
t
End-of-Charge Comparator Filter Time
I
Falling
BAT
BAT
R
Battery Charger Power FET On-
Resistance (Between V and BAT)
I
= 190mA
mΩ
ON(CHG)
CC
T
Junction Temperature in Constant
Temperature Mode
105
°C
LIM
NTC
V
V
V
Cold Temperature Fault Threshold
Voltage
Hot Temperature Fault Threshold
Voltage
Rising NTC Voltage
Hysteresis
Falling NTC Voltage
Hysteresis
Falling NTC Voltage
Hysteresis
75
33.4
0.7
–1
76.5
1.6
34.9
1.6
1.7
50
78
36.4
2.7
1
%V
%V
%VCC
%VCC
%V
CC
mV
μA
COLD
HOT
DIS
CC
CC
l
NTC Disable Threshold Voltage
I
NTC Leakage Current
V = V = 5V
NTC CC
NTC
3558f
3
LTC3558
ELECTRICAL CHARACTERISTICS The l denotes specifications that apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. VCC = 5V, BAT = PVIN1 = PVIN2 = 3.6V, RPROG = 1.74k, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Logic (HPWR, SUSP, CHRG, EN1, EN2, MODE)
V
V
Input Low Voltage
HPWR, SUSP, MODE, EN1, EN2 Pins
HPWR, SUSP, MODE, EN1, EN2 Pins
HPWR, SUSP Pins
0.4
V
V
IL
Input High Voltage
1.2
1.9
IH
l
R
Logic Pin Pull-Down Resistance
CHRG Pin Output Low Voltage
CHRG Pin Input Current
4
100
0
6.3
250
1
MΩ
mV
μA
DN
V
I
= 5mA
CHRG
CHRG
CHRG
I
BAT = 4.5V, V
= 5V
CHRG
Buck Switching Regulator
l
l
PV
Input Supply Voltage
2.7
4.2
V
IN1
I
Pulse Skip Input Current
Burst Mode Current
Shutdown Current
FB1 = 0.85V, MODE = 0 (Note 6)
FB1 = 0.85V, MODE = 1 (Note 6)
EN1 = 0
220
35
0
400
50
2
μA
μA
μA
μA
PVIN1
Supply Current in UVLO
PV = PV = 2V
4
8
IN1
IN2
l
l
PV UVLO
PV Falling
IN1
Switching Frequency
Peak PMOS Current Limit
Feedback Voltage
2.30
2.45
2.55
2.25
800
800
V
V
IN1
IN1
PV Rising
2.70
2.59
f
I
MODE = 0
MODE = 0
1.91
550
780
–50
100
MHz
mA
mV
nA
%
OSC
1050
820
50
LIMSW1
l
l
V
FB1
FB1
I
FB Input Current
FB1 = 0.85V
FB1 = 0V
D
R
R
R
Maximum Duty Cycle
MAX1
R
R
of PMOS
of NMOS
I
I
= 100mA
0.65
0.75
13
Ω
PMOS1
NMOS1
SW1(PD)
DS(ON)
DS(ON)
SW1
SW1
= –100mA
Ω
SW Pull-Down in Shutdown
kΩ
Buck-Boost Switching Regulator
l
PV
IN2
Input Supply Voltage
2.7
4.2
V
I
PWM Input Current
MODE = 0, I
MODE = 1, I
= 0A, FB2 = 0.85V (Note 6)
= 0A, FB2 = 0.85V (Note 6)
220
20
0
400
30
1
μA
μA
μA
μA
PVIN2
OUT
OUT
Burst Mode Input Current
Shutdown Current
EN2 = 0, I
= 0A
OUT
Supply Current in UVLO
PV = PV = 2V
4
8
IN1
IN2
l
l
PV UVLO
PV Falling
IN2
Minimum Regulated Buck-Boost V
2.30
2.45
2.55
V
V
V
IN2
IN2
PV Rising
2.70
2.75
V
V
2.65
5.60
700
250
450
0
OUT2(LOW)
OUT2(HIGH)
LIMF2
OUT
Maximum Regulated Buck-Boost V
Forward Current Limit (Switch A)
Forward Current Limit (Switch A)
Reverse Current Limit (Switch D)
Reverse Current Limit (Switch D)
5.45
580
180
325
–35
50
V
OUT
l
l
l
l
I
I
I
I
I
MODE = 0
MODE = 1
MODE = 0
MODE = 1
820
320
575
35
mA
mA
mA
mA
mA
PEAK2(BURST)
LIMR2
ZERO2(BURST)
MAX2(BURST)
Maximum Deliverable Output Current
in Burst Mode Operation
2.7V < PV < 4.2V
IN2
2.75V < V
< 5.5V
OUT2
l
V
Feedback Servo Voltage
780
–50
1.91
800
820
50
mV
nA
FB2
I
f
FB2 Input Current
FB2 = 0.85V
MODE = 0
FB2
Switching Frequency
2.25
2.59
MHz
OSC
3558f
4
LTC3558
ELECTRICAL CHARACTERISTICS The l denotes specifications that apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. VCC = 5V, BAT = PVIN1 = PVIN2 = 3.6V, RPROG = 1.74k, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
= 3.6V
MIN
TYP
MAX
UNITS
Ω
R
PMOS R
V
OUT
0.6
DSP(ON)
DS(ON)
R
NMOS R
0.6
Ω
DSN(ON)
DS(ON)
I
I
PMOS Switch Leakage
NMOS Switch Leakage
Maximum Buck Duty Cycle
Maximum Boost Duty Cycle
Soft-Start Time
Switches A, D
Switches B, C
MODE = 0
–1
–1
1
1
μA
μA
%
LEAK(P)
LEAK(N)
l
DC
DC
100
BUCK(MAX)
MODE = 0
75
0.5
10
%
BOOST(MAX)
t
ms
SS2
R
V
Pull-Down in Shutdown
OUT
kΩ
OUT(PD)
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 4: V supply current does not include current through the PROG pin
or any current delivered to the BAT pin. Total input current is equal to this
CC
specification plus 1.00125 • I where I is the charge current.
BAT
BAT
Note 5: I
is expressed as a fraction of measured full charge current
C/10
Note 2: T is calculated from the ambient temperature T and power
with indicated PROG resistor.
J
A
dissipation P according to the following formula:
D
Note 6: Dynamic supply current is higher due to the gate charge being
T = T + (P • θ )
JA
delivered at the switching frequency.
J
A
D
Note 3: The LTC3558E is guaranteed to meet 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.
3558f
5
LTC3558
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
Battery Regulation (Float) Voltage
vs Battery Charge Current,
Constant-Voltage Charging
Suspend State Supply and BAT
Currents vs Temperature
Battery Regulation (Float)
Voltage vs Temperature
10
9
8
7
6
5
4
3
2
1
0
4.24
4.205
4.200
4.195
4.190
4.185
4.180
4.175
4.170
4.165
4.160
4.155
4.150
V
= 5V
CC
4.23
4.22
I
VCC
4.21
4.20
4.19
4.18
4.17
V
= 5V
CC
BAT = 4.2V
SUSP = 5V
EN1 = EN2 = 0V
V
= 5V
CC
I
BAT
HPWR = 5V
R
= 845Ω
PROG
EN1 = EN2 = 0V
4.16
–55
–15
5
25
45
65
85
–35 –15
25
45
65
85
–35
–55
5
0
100 200 300 400 500 600 700 800 9001000
TEMPERATURE (°C)
TEMPERATURE (°C)
I
(mA)
BAT
3558 G01
3558 G02
3558 G03
Battery Charge Current vs Ambient
Temperature in Thermal Regulation
Battery Charge Current
vs Supply Voltage
Battery Charge Current
vs Battery Voltage
500
495
490
485
480
475
470
465
460
455
450
445
440
500
450
400
350
300
250
200
150
100
50
500
450
400
350
300
250
200
150
100
50
V
= 5V
HPWR = 5V
V
= 5V
PROG
CC
CC
HPWR = 5V
= 1.74k
R
= 1.74k
R
PROG
EN1 = EN2 = 0V
V
= 5V
HPWR = 0V
3.5
CC
HPWR = 5V
= 1.74k
R
PROG
EN1 = EN2 = 0
0
0
4.3 4.4
4.6
4.8 4.9 5.0 5.1 5.2 5.3 5.4 5.5
4.7
4.5
–55 –35 –15
5
25 45 65 85 105 125
2
2.5
3
4
4.5
V
(V)
TEMPERATURE (°C)
CC
V
(V)
BAT
3558 G04
3558 G06
3558 G05
Battery Drain Current in Undervoltage
Lockout vs Temperature
Battery Charger Undervoltage
PROG Voltage
Lockout Threshold vs Temperature
vs Battery Charge Current
1.2
1.0
4.2
4.1
3.0
2.5
2.0
1.5
V
= 5V
BAT = 3.5V
CC
EN1 = EN2 = 0V
HPWR = 5V
= 1.74k
R
PROG
RISING
EN1 = EN2 = 0V
BAT = 4.2V
4.0
3.9
3.8
3.7
3.6
0.8
0.6
BAT = 3.6V
FALLING
0.4
0.2
0
1.0
0.5
0
3.5
0
50 100 150 200 250 300 350 400 450 500
(mA)
25
TEMPERATURE (°C)
65
85
–55 –35 –15
5
45
25
TEMPERATURE (°C)
65
85
–55 –35 –15
5
45
I
BAT
3558 G09
3558 G07
3558 G08
3558f
6
LTC3558
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, unless otherwise noted.
Recharge Threshold
vs Temperature
Battery Charger FET
SUSP/HPWR Pin Rising
On-Resistance vs Temperature
Thresholds vs Temperature
115
111
107
103
99
1.2
700
650
600
550
500
450
400
350
300
V
= 5V
V
= 5V
V
BAT
EN1 = EN2 = 0V
= 4V
CC
CC
CC
I
= 200mA
1.1
1.0
0.9
0.8
0.7
0.6
0.5
95
91
87
83
79
75
0.4
–55
–15
5
25
45
65
85
–55
–35 –15
5
25
45
65
85
–35
–15
5
25
45
65
85
–55 –35
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
3558 G10
3558 G12
3558 G11
CHRG Pin Output Low Voltage
vs Temperature
CHRG Pin I-V Curve
Timer Accuracy vs Supply Voltage
140
120
2.0
1.5
1.0
0.5
0
70
60
50
40
30
20
10
0
V
I
= 5V
CHRG
V
= 5V
CC
CC
= 5mA
BAT = 3.8V
100
80
60
40
20
–0.5
–1.0
0
25
TEMPERATURE (°C)
65
85
–55 –35 –15
5
45
4.3
4.7
4.9
(V)
5.1
5.3
5.5
4.5
4
6
0
1
2
3
5
V
CC
CHRG (V)
3558 G13
3558 G15
3558 G14
Complete Charge Cycle
2400mAh Battery
Buck and Buck-Boost Regulator
Switching Frequency vs Temperature
Timer Accuracy vs Temperature
2.425
2.325
2.225
2.125
2.025
1.925
1.825
1.725
7
6
1000
800
600
400
200
0
5.0
4.5
4.0
3.5
3.0
5.0
4.0
3.0
2.0
1.0
0
V
= 5V
V
= 0V, MODE = 0
CC
CC
V
= 5V
CC
PROG
BAT = PV = PV
IN1
IN2
R
= 0.845k
HPWR = 5V
5
BAT = 4.2V
BAT = 3.6V
4
BAT = 2.7V
3
2
1
0
–1
–2
–55 –35 –15
5
25 45 65 85 105 125
–55 –35 –15
5
85
0
1
2
3
4
5
6
25
45
65
TEMPERATURE (°C)
TEMPERATURE (°C)
TIME (HOUR)
3558 G17
3558 G18
3558 G16
3558f
7
LTC3558
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
Buck and Buck-Boost Regulator
Undervoltage Thresholds
vs Temperature
Buck and Buck-Boost Regulator
Enable Thresholds
Buck Regulator Input Current vs
Temperature, Burst Mode Operation
vs Temperature
1200
1100
1000
900
2.750
2.700
2.650
2.600
2.550
2.500
2.450
2.400
2.350
2.300
2.250
50
45
BAT = PV = PV = 3.6V
BAT = PV = PV
FB1 = 0.85V
IN1
IN2
IN1
IN2
RISING
40
PV = 4.2V
IN1
800
35
30
FALLING
RISING
PV = 2.7V
IN1
700
FALLING
600
25
20
500
400
–55 –35 –15
5
25 45 65 85 105 125
–55 –35 –15
5
25 45 65 85 105 125
–55 –35 –15
5
25 45 65 85 105 125
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
3558 G20
3558 G19
3558 G21
Buck Regulator Input Current vs
Temperature, Pulse Skip Mode
Buck Regulator PMOS RDS(0N)
vs Temperature
Buck Regulator NMOS RDS(0N)
vs Temperature
1300
1200
1100
1000
900
1300
1200
1100
1000
900
400
350
FB1 = 0.85V
300
PV = 2.7V
IN1
PV = 4.2V
IN1
250
200
PV = 2.7V
IN1
800
800
PV = 2.7V
IN1
PV = 4.2V
IN1
PV = 4.2V
IN1
700
700
600
600
150
100
500
500
400
400
–55 –35 –15
5
25 45
125
–55 –35 –15
5
25 45
125
65 85 105
65 85 105
–55 –35 –15
5
25 45 65 85 105 125
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
3558 G23
3558 G24
3558 G22
Buck Regulator Efficiency vs ILOAD
Buck Regulator Load Regulation
Buck Regulator Line Regulation
100
90
80
70
60
50
40
30
20
10
0
1.250
1.240
1.230
1.220
1.210
1.200
1.190
1.180
1.170
1.160
1.150
1.25
1.24
1.23
1.22
I
= 200mA
LOAD
PV = 3.6V
IN1
OUT
Burst Mode
OPERATION
V
= 1.2V
Burst Mode
OPERATION
1.21
1.20
PULSE SKIP
MODE
PULSE SKIP
MODE
1.19
1.18
1.17
1.16
1.15
V
= 1.2V
OUT
PV = 2.7V
IN1
PV = 4.2V
IN1
0.1
1
10
(mA)
100
1000
2.700
3.000
3.300
3.600
3.900
4.200
1
10
100
1000
I
PV (V)
IN1
LOAD
I
(mA)
LOAD
3558 G25
3558 G27
3558 G26
3558f
8
LTC3558
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
Buck Regulator
Pulse Skip Mode Operation
Buck Regulator
Burst Mode Operation
Buck Regulator Start-Up Transient
V
OUT
V
OUT
V
OUT
20mV/
20mV/
500mV/DIV
DIV (AC)
DIV (AC)
SW
INDUCTOR
CURRENT
SW
2V/DIV
2V/DIV
I
= 200mA/
DIV
L
INDUCTOR
CURRENT
= 50mA/
DIV
INDUCTOR
CURRENT
= 60mA/
DIV
EN
2V/DIV
I
L
I
L
3558 G29
3558 G28
3558 G30
PV = 3.8V
IN1
LOAD = 10mA
200ns/DIV
PV = 3.8V
IN1
50μs/DIV
PULSE SKIP MODE
LOAD = 6Ω
PV = 3.8V
IN1
LOAD = 60mA
2μs/DIV
Buck Regulator Transient
Response, Pulse Skip Mode
Buck Regulator Transient
Response, Burst Mode Operation
Buck-Boost Regulator Input
Current vs Temperature
30
25
20
15
10
5
INDUCTOR
CURRENT
INDUCTOR
CURRENT
Burst Mode OPERATION
FB2 = 0.85V
I = 200mA/
I
= 200mA/
L
L
DIV
DIV
PV = 4.2V
IN2
V
OUT
V
OUT
50mV/
50mV/
PV = 2.7V
IN2
DIV (AC)
DIV (AC)
LOAD STEP
5mA TO
290mA
LOAD STEP
5mA TO
290mA
3558 G32
3558 G31
PV = 3.8V
IN1
50μs/DIV
PV = 3.8V
IN1
50μs/DIV
–55 –35 –15
5
25 45 65 85 105 125
TEMPERATURE (°C)
3558 G33
Buck-Boost Regulator NMOS
RDS(ON) vs Temperature
Buck-Boost Regulator Input
Current vs Temperature
Buck-Boost Regulator PMOS
RDS(ON) vs Temperature
500
450
400
350
300
250
200
150
100
800
750
700
650
600
550
500
450
400
350
300
250
200
1200
1100
1000
900
800
700
600
500
400
300
200
PWM MODE
FB2 = 0.85V
PV = 2.7V
IN2
PV = 2.7V
IN2
PV = 4.2V
IN2
PV = 4.2V
IN2
PV = 2.7V
IN2
PV = 4.2V
IN2
–55 –35 –15
5
25 45 65 85 105 125
–55 –35 –15
5
45
85 105 125
25
65
85
105 125
–55 –35 –15
5
25 45 65
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
3558 G35
3558 G34
3558 G36
3558f
9
LTC3558
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, unless otherwise noted.
Buck-Boost Efficiency
vs Load Current
Buck-Boost Regulator
Efficiency vs Input Voltage
100
90
80
70
60
50
40
30
20
100
95
90
85
80
75
70
65
60
55
50
V
= 3.3V
V
= 3.3V
OUT
OUT
I
= 10mA
LOAD
I
= 1mA
3.6V
4.2V
LOAD
2.7V
I
= 100mA
LOAD
I
= 400mA
LOAD
2.7V
Burst Mode
OPERATION
PWM MODE
PV , Burst Mode
IN2
3.6V
4.2V
OPERATION
10
0
0.10
PV , PWM MODE
IN2
2.700
3.000
3.300
3.600
3.900
4.200
1
10
(mA)
100
1000
I
PV (V)
IN2
LOAD
3558 G37
3558 G38
Buck-Boost Regulator
Load Regulation
Buck-Boost Regulator
Line Regulation
3.36
3.35
3.34
3.33
3.32
3.31
3.30
3.29
3.28
3.27
3.26
3.25
3.24
3.36
3.35
3.34
3.33
3.32
3.31
3.30
3.29
3.28
3.27
3.26
3.25
3.24
PV = 3.6V
IN2
Burst Mode OPERATION
PWM MODE
I
= 100mA
LOAD
PWM MODE
Burst Mode
OPERATION
I
= 10mA
LOAD
2.700
3.000
3.300
3.600
3.900
4.200
0.10
1
10
(mA)
100
1000
PV (V)
IN2
I
LOAD
3558 G40
3558 G39
Buck-Boost Regulator Start-Up
Transient, Burst Mode Operation
Buck-Boost Regulator Start-Up
Transient, PWM Mode
PV = 3.6V
IN2
LOAD
PV = 3.6V
IN2
LOAD
R
= 16Ω
R
= 332Ω
V
V
OUT
OUT
1V/DIV
1V/DIV
INDUCTOR
CURRENT
I = 200mA/DIV
L
INDUCTOR
CURRENT
I = 200mA/DIV
L
EN2
1V/DIV
EN2
1V/DIV
3558 G42
3558 G41
100μs/DIV
100μs/DIV
3558f
10
LTC3558
PIN FUNCTIONS
GND (Pin 1): Ground. Connect to Exposed Pad (Pin 21).
V
C2
(Pin 14): Output of the Error Amplifier and Voltage
Compensation Node for the Buck-Boost Regulator. Ex-
ternal Type I or Type III compensation (to FB2) connects
to this pin.
BAT (Pin 2): Charge Current Output. Provides charge cur-
rent to the battery and regulates final float voltage to 4.2V.
MODE (Pin 3): MODE Pin for Switching Regulators. When
held high, both regulators operate in Burst Mode Opera-
tion. When held low, the buck regulator operates in pulse
skip mode and the buck-boost regulator operates in PWM
mode. This pin is a high impedance input; do not float.
EN2 (Pin 15): Enable Input Pin for the Buck-Boost Regu-
lator. This pin is a high impedance input; do not float.
Active high.
HPWR (Pin 16): High Current Battery Charging Enabled.
A voltage greater than 1.2V at this pin programs the
BAT pin current at 100% of the maximum programmed
charge current. A voltage less than 0.4V sets the BAT pin
current to 20% of the maximum programmed charge
current. When used with a 1.74k PROG resistor, this pin
can toggle between low power and high power modes per
USB specification. A weak pull-down current is internally
applied to this pin to ensure it is low at power-up when
the input is not being driven externally.
FB1 (Pin 4): Buck Regulator Feedback Voltage Pin. Re-
ceives feedback by a resistor divider connected across
the output.
EN1 (Pin 5): Enable Input Pin for the Buck Regulator. This
pin is a high impedance input; do not float. Active high.
SW1 (Pin 6): Buck Regulator Switching Node. External
inductor connects to this node.
PV (Pin 7): Input Supply Pin for Buck Regulator. Con-
IN1
NTC (Pin 17): Input to the NTC Thermistor Monitoring
Circuit. The NTC pin connects to a negative temperature
coefficient thermistor which is typically co-packaged with
thebatterypacktodetermineifthebatteryistoohotortoo
cold to charge. If the battery temperature is out of range,
charging is paused until the battery temperature re-enters
the valid range. A low drift bias resistor is required from
nect to BAT and PV . A single 10μF input decoupling
IN2
capacitor to GND is required.
PV (Pin 8): Input Supply Pin for Buck-Boost Regulator.
IN2
Connect to BAT and PV . A single 10μF input decoupling
IN1
capacitor to GND is required.
SWAB2 (Pin 9): Switch Node for Buck-Boost Regulator
ConnectedtotheInternalPowerSwitchesAandB.External
inductor connects between this node and SWCD2.
V
to NTC and a thermistor is required from NTC to
CC
ground. To disable the NTC function, the NTC pin should
be tied to ground.
SWCD2 (Pin 10): Switch Node for Buck-Boost Regulator
ConnectedtotheInternalPowerSwitchesCandD.External
inductor connects between this node and SWAB2.
PROG (Pin 18): Charge Current Program and Charge
Current Monitor Pin. Charge current is programmed by
connecting a resistor from PROG to ground. When charg-
ing in constant-current mode, the PROG pin servos to 1V
if the HPWR pin is pulled high, or 200mV if the HPWR pin
is pulled low. The voltage on this pin always represents
the BAT pin current through the following formula:
V
(Pin 11): Regulated Output Voltage for Buck-Boost
OUT2
Regulator.
SUSP (Pin 12): Suspend Battery Charging Operation. A
voltage greater than 1.2V on this pin puts the battery char-
ger in suspend mode, disables the charger and resets the
termination timer. A weak pull-down current is internally
applied to this pin to ensure it is low at power-up when
the input is not being driven externally.
PROG •800
IBAT
=
RPROG
CHRG (Pin 19): Open-Drain Charge Status Output. The
CHRG pin indicates the status of the battery charger. Four
possible states are represented by CHRG charging, not
charging (i.e., the charge current is less than one-tenth
FB2 (Pin 13): Buck-Boost Regulator Feedback Voltage
Pin. Receives feedback by a resistor divider connected
across the output.
3558f
11
LTC3558
PIN FUNCTIONS
of the full-scale charge current), unresponsive battery
(i.e., the battery voltage remains below 2.9V after one half
hour of charging) and battery temperature out of range.
CHRG requires a pull-up resistor and/or LED to provide
indication.
V
(Pin 20): Battery Charger Input. A 1μF decoupling
CC
capacitor to GND is recommended.
Exposed Pad (Pin 21): Ground. The Exposed Pad must
be soldered to PCB ground to provide electrical contact
and rated thermal performance.
BLOCK DIAGRAM
20
V
CC
V
BAT
BODY
CC
1x
800x
MAXER
BAT
2
–
+
CHRG
HPWR
SUSP
19
16
12
T
CA
A
LOGIC
T
DIE
PROG
18
NTCA
NTC REF
NTC
17
3
BATTERY CHARGER
PV
IN1
PV
IN2
MODE
PV
IN1
7
6
EN1
EN2
FB1
5
15
4
UNDERVOLTAGE
LOCKOUT
EN MODE
CLK
MP
MN
–
+
SW1
CONTROL
LOGIC
G
OT
m
DIE
0.8V
T
DIE
TEMPERATURE
BUCK REGULATOR
PV
IN2
V
REF
8
BANDGAP
= 0.8V
V
OUT2
11
BUCK-BOOST REGULATOR
OSCILLATOR
2.25MHz
CLK
EN MODE
A
B
D
C
CLK
–
SWAB2
SWCD2
FB2
9
13
14
CONTROL
LOGIC
V
C2
ERROR
10
AMP
+
0.8V
V
C2
GND
1
EXPOSED PAD
21
3558 BD
3558f
12
LTC3558
OPERATION
The LTC3558 is a linear battery charger with a monolithic
synchronous buck regulator and a monolithic synchro-
nous buck-boost regulator. The buck regulator is inter-
nally compensated and needs no external compensation
components.
For proper operation, the BAT, PV
and PV
pins
IN2
IN1
must be tied together, as shown in Figure 1. Cur-
rent being delivered at the BAT pin is 500mA. Both
switching regulators are enabled. The sum of the
averageinputcurrentsdrawnbybothswitchingregulators
is 200mA. This makes the effective battery charging cur-
rent only 300mA. If the HPWR pin were tied LO, the BAT
pin current would be 100mA. With the switching regulator
conditions unchanged, this would cause the battery to
discharge at 100mA.
Thebatterychargeremploysaconstant-current,constant-
voltage charging algorithm and is capable of charging a
singleLi-Ionbatteryatchargingcurrentsupto950mA.The
usercanprogramthemaximumchargingcurrentavailable
at the BAT pin via a single PROG resistor. The actual BAT
pin current is set by the status of the HPWR pin.
500mA
300mA
USB (5V)
V
BAT
CC
+
SINGLE Li-lon
CELL 3.6V
200mA
PV
IN1
PROG
PV
+
IN2
LTC3558
10μF
R
PROG
SUSP
SWAB2
HIGH
2.2μH
HPWR
EN1
HIGH
SWCD2
OUT2
SW1
HIGH
LOW
EN2
V
MODE
V
OUT1
3558 F01
Figure 1. For Proper Operation, the BAT, PVIN1 and PVIN2 Pins Must Be Tied Together
APPLICATIONS INFORMATION
Battery Charger Introduction
Input Current vs Charge Current
The LTC3558 has a linear battery charger designed to
charge single-cell lithium-ion batteries. The charger uses
a constant-current/constant-voltage charge algorithm
with a charge current programmable up to 950mA. Ad-
ditional features include automatic recharge, an internal
terminationtimer,low-batterytricklechargeconditioning,
bad-battery detection, and a thermistor sensor input for
out of temperature charge pausing.
The battery charger regulates the total current delivered
to the BAT pin; this is the charge current. To calculate the
total input current (i.e., the total current drawn from the
V
pin), it is necessary to sum the battery charge current,
CC
charger quiescent current and PROG pin current.
Undervoltage Lockout (UVLO)
The undervoltage lockout circuit monitors the input volt-
age (V ) and disables the battery charger until V rises
Furthermore, the battery charger is capable of operating
from a USB power source. In this application, charge
current can be programmed to a maximum of 100mA or
500mA per USB power specifications.
CC
CC
above V
(typically 4V). 200mV of hysteresis prevents
UVLO
oscillations around the trip point. In addition, a differential
undervoltage lockout circuit disables the battery charger
3558f
13
LTC3558
APPLICATIONS INFORMATION
when V falls to within V
(typically 50mV) of the
enters constant-voltage mode, the 4-hour timer is started.
After the safety timer expires, charging of the battery will
discontinue and no more current will be delivered.
CC
DUVLO
BAT voltage.
Suspend Mode
Automatic Recharge
The battery charger can also be disabled by pulling the
SUSP pin above 1.2V. In suspend mode, the battery
drain current is reduced to 1.5μA and the input current is
reduced to 8.5μA.
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
battery is always topped off, a charge cycle will automati-
Charge Cycle Overview
cally begin when the battery voltage falls below V
RECHRG
When a battery charge cycle begins, the battery charger
first determines if the battery is deeply discharged. If the
(typically 4.105V). In the event that the safety timer is
running when the battery voltage falls below V , it
RECHRG
batteryvoltageisbelowV
,typically2.9V,anautomatic
TRKL
will reset back to zero. To prevent brief excursions below
trickle charge feature sets the battery charge current to
V
fromresettingthesafetytimer,thebatteryvoltage
RECHRG
must be below V
10% of the full-scale value.
for more than 1.7ms. The charge
RECHRG
cycle and safety timer will also restart if the V UVLO or
Once the battery voltage is above 2.9V, the battery charger
begins charging in constant-current mode. When the
battery voltage approaches the 4.2V required to maintain
a full charge, otherwise known as the float voltage, the
charge current begins to decrease as the battery charger
switches into constant-voltage mode.
CC
DUVLO cycles low and then high (e.g., V is removed
CC
and then replaced) or the charger enters and then exits
suspend mode.
Programming Charge Current
The PROG pin serves both as a charge current program
pin, and as a charge current monitor pin. By design, the
PROG pin current is 1/800th of the battery charge current.
Therefore, connecting a resistor from PROG to ground
programsthechargecurrentwhilemeasuringthePROGpin
voltage allows the user to calculate the charge current.
Trickle Charge and Defective Battery Detection
Any time the battery voltage is below V , the charger
TRKL
goes into trickle charge mode and reduces the charge
current to 10% of the full-scale current. If the battery
voltage remains below V
for more than 1/2 hour, the
TRKL
chargerlatchesthebad-batterystate, automaticallytermi-
nates, and indicates via the CHRG pin that the battery was
unresponsive. If for any reason the battery voltage rises
Full-scale charge current is defined as 100% of the con-
stant-current mode charge current programmed by the
PROG resistor. In constant-current mode, the PROG pin
servosto1VifHPWRishigh,whichcorrespondstocharg-
ing at the full-scale charge current, or 200mV if HPWR
is low, which corresponds to charging at 20% of the full-
scale charge current. Thus, the full-scale charge current
and desired program resistor for a given full-scale charge
current are calculated using the following equations:
above V
, the charger will resume charging. Since the
TRKL
charger has latched the bad-battery state, if the battery
voltagethenfallsbelowV againbutwithoutrisingpast
TRKL
V
first, the charger will immediately assume that
RECHRG
the battery is defective. To reset the charger (i.e., when
the dead battery is replaced with a new battery), simply
remove the input voltage and reapply it or put the part in
and out of suspend mode.
800V
RPROG
ICHG
=
Charge Termination
800V
ICHG
RPROG
=
The battery charger has a built-in safety timer that sets
the total charge time for 4 hours. Once the battery voltage
rises above V
(typically 4.105V) and the charger
RECHRG
3558f
14
LTC3558
APPLICATIONS INFORMATION
In any mode, the actual battery current can be determined
by monitoring the PROG pin voltage and using the follow-
ing equation:
charge current has dropped to below 10% of the full-scale
current, the CHRG pin is released (high impedance). If
a fault occurs after the CHRG pin is released, the pin re-
mains high impedance. However, if a fault occurs before
the CHRG pin is released, the pin is switched at 35kHz.
Whileswitching,itsdutycycleismodulatedbetweenahigh
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”.
Each of the two faults has its own unique “blink” rate for
human recognition as well as two unique duty cycles for
microprocessor recognition.
PROG
RPROG
IBAT
=
•800
Thermal Regulation
To prevent thermal damage to the IC or surrounding
components, an internal thermal feedback loop will auto-
matically decrease the programmed charge current if the
die temperature rises to approximately 115°C. Thermal
regulation protects the battery charger 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 without risk of damaging the LTC3558 or external
components. The benefit of the LTC3558 battery charger
thermal regulation loop is that charge current can be set
according to actual conditions rather than worst-case
conditions with the assurance that the battery charger
will automatically reduce the current in worst-case con-
ditions.
Table 1 illustrates the four possible states of the CHRG
pin when the battery charger is active.
Table 1. CHRG Output Pin
MODULATION
(BLINK)
STATUS
FREQUENCY
0Hz
FREQUENCY
DUTY CYCLE
100%
Charging
0 Hz (Lo-Z)
I
< C/10
0Hz
0 Hz (Hi-Z)
0%
BAT
35kHz
35kHz
1.5Hz at 50%
6.1Hz at 50%
6.25%, 93.75%
12.5%, 87.5%
NTC Fault
Bad Battery
An NTC fault is represented by a 35kHz pulse train whose
duty cycle alternates between 6.25% and 93.75% at a
1.5Hz rate. A human will easily recognize the 1.5Hz rate as
a “slow” blinking which indicates the out of range battery
temperaturewhileamicroprocessorwillbeabletodecode
either the 6.25% or 93.75% duty cycles as an NTC fault.
Charge Status Indication
The CHRG pin indicates the status of the battery charger.
Four possible states are represented by CHRG charging,
notcharging,unresponsivebatteryandbatterytemperature
out of range.
If a battery is found to be unresponsive to charging (i.e.,
ThesignalattheCHRGpincanbeeasilyrecognizedasone
of the above four states by either a human or a micropro-
cessor. The CHRG pin, which is an open-drain output, can
drive an indicator LED through a current limiting resistor
for human interfacing, or simply a pull-up resistor for
microprocessor interfacing.
its voltage remains below V
for over 1/2 hour), the
TRKL
CHRG pin gives the battery fault indication. For this fault,
a human would easily recognize the frantic 6.1Hz “fast”
blinking of the LED while a microprocessor would be able
to decode either the 12.5% or 87.5% duty cycles as a bad
battery fault.
To make the CHRG pin easily recognized by both humans
and microprocessors, the pin is either a low for charging,
a 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.
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.
When charging begins, CHRG is pulled low and remains
low for the duration of a normal charge cycle. When the
3558f
15
LTC3558
APPLICATIONS INFORMATION
NTC Thermistor
value of R25 or approximately 54k (for a Vishay “Curve
1” thermistor, this corresponds to approximately 40°C). If
thebatterychargerisinconstant-voltagemode, thesafety
timer will pause until the thermistor indicates a return to
a valid temperature.
The battery temperature is measured by placing a nega-
tive temperature coefficient (NTC) thermistor close to the
battery pack. The NTC circuitry is shown in Figure 3.
To use this feature, connect the NTC thermistor, R
,
,
NTC
NOM
As the temperature drops, the resistance of the NTC
thermistor rises. The battery charger is 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” thermistor, this resistance, 325k, corresponds
to approximately 0°C. The hot and cold comparators each
haveapproximately3°Cofhysteresistopreventoscillation
about the trip point. Grounding the NTC pin disables all
NTC functionality.
betweentheNTCpinandground,andabiasresistor,R
from V to NTC. R
should be a 1% resistor with a
CC
NOM
value equal to the value of the chosen NTC thermistor at
25°C (R25). A 100k thermistor is recommended since
thermistor current is not measured by the battery charger
and its current will have to be considered for compliance
with USB specifications.
The battery charger will pause charging when the re-
sistance of the NTC thermistor drops to 0.54 times the
DUVLO, UVLO AND SUSPEND
IF SUSP < 0.4V AND
DISABLE MODE
NO
POWER
CHRG HIGH IMPEDANCE
ON
V
CC
V
CC
> 4V AND
> BAT + 130mV?
YES
FAULT
NTC FAULT
STANDBY MODE
BATTERY CHARGING SUSPENDED
NO CHARGE CURRENT
CHRG PULSES
CHRG HIGH IMPEDANCE
NO FAULT
BAT b 2.9V
2.9V < BAT < 4.105V
BAT > 2.9V
TRICKLE CHARGE MODE
CONSTANT CURRENT MODE
4-HOUR
TIMEOUT
1/10 FULL CHARGE CURRENT
CHRG STRONG PULL-DOWN
30 MINUTE TIMER BEGINS
FULL CHARGE CURRENT
CHRG STRONG PULL-DOWN
30 MINUTE
TIMEOUT
DEFECTIVE BATTERY
CONSTANT VOLTAGE MODE
NO CHARGE CURRENT
CHRG PULSES
4-HOUR TERMINATION TIMER
BEGINS
BAT DROPS BELOW 4.105V
4-HOUR TERMINATION TIMER RESETS
3558 F02
Figure 2. State Diagram of Battery Charger Operation
3558f
16
LTC3558
APPLICATIONS INFORMATION
Alternate NTC Thermistors and Biasing
Therefore, the hot trip point is set when:
The battery charger provides temperature qualified
charging if a grounded thermistor and a bias resistor are
connected to the NTC pin. 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).
RNTC|HOT
• VCC = 0.349 • VCC
RNOM + RNTC|HOT
and the cold trip point is set when:
RNTC|COLD
• VCC = 0.765 • VCC
RNOM + RNTC|COLD
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
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.
Solving these equations for R
results in the following:
and R
NTC|HOT
NTC|COLD
R
= 0.536 • R
NTC|HOT
NOM
and
R
= 3.25 • R
NTC|COLD
NOM
By setting R
equal to R25, the above equations result
NOM
= 0.536 and r
in r
= 3.25. Referencing these ratios
HOT
COLD
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.
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.
By using a bias resistor, R
, different in value from
NOM
R25, the hot and cold trip points can be moved in either
direction.Thetemperaturespanwillchangesomewhatdue
to the nonlinear behavior of the thermistor. The following
equations can be used to easily calculate a new value for
the bias resistor:
In the explanation below, the following notation is used.
R25 = Value of the thermistor at 25°C
rHOT
0.536
RNOM
=
•R25
R
R
= Value of thermistor at the cold trip point
NTC|COLD
= Value of the thermistor at the hot trip point
NTC|HOT
rCOLD
3.25
and r
RNOM
=
•R25
r
r
= Ratio of R
to R25
COLD
NTC|COLD
where r
are the resistance ratios at the de-
COLD
= Ratio of R
to R25
HOT
HOT
NTC|HOT
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.
R
= Primary thermistor bias resistor (see Figure 3)
NOM
R1 = Optional temperature range adjustment resistor (see
Figure 4)
The trip points for the battery charger’s temperature quali-
FromtheVishayCurve1R-Tcharacteristics,r is0.2488
fication are internally programmed at 0.349 • V for the
HOT
should be set
CC
at 60°C. Using the above equation, R
hot threshold and 0.765 • V for the cold threshold.
NOM
CC
3558f
17
LTC3558
APPLICATIONS INFORMATION
to 46.4k. With this value of R
, the cold trip point is
For example, to set the trip points to 0°C and 45°C with
a Vishay Curve 1 thermistor choose:
NOM
about 16°C. Notice that the span is now 44°C rather than
the previous 40°C.
3.266 – 0.4368
RNOM
=
•100k = 104.2k
The upper and lower temperature trip points can be inde-
pendentlyprogrammedbyusinganadditionalbiasresistor
as shown in Figure 4. The following formulas can be used
2.714
the nearest 1% value is 105k.
to compute the values of R
and R1:
NOM
R1 = 0.536 • 105k – 0.4368 • 100k = 12.6k
rCOLD –rHOT
the nearest 1% value is 12.7k. The final solution is shown
in Figure 4 and results in an upper trip point of 45°C and
a lower trip point of 0°C.
RNOM
=
•R25
2.714
R1= 0.536 •RNOM –rHOT •R25
NTC BLOCK
V
V
CC
CC
20
20
17
0.765 • V
CC
0.765 • V
CC
(NTC RISING)
(NTC RISING)
R
–
+
–
+
R
NOM
NOM
105k
100k
TOO_COLD
TOO_HOT
TOO_COLD
TOO_HOT
NTC
NTC
17
R1
12.7k
R
100k
NTC
–
+
–
+
R
100k
NTC
0.349 • V
0.349 • V
CC
(NTC FALLING)
CC
(NTC FALLING)
+
–
+
–
NTC_ENABLE
NTC_ENABLE
0.017 • V
CC
(NTC FALLING)
0.017 • V
CC
(NTC FALLING)
3558 F04
3558 F03
Figure 4. NTC Thermistor Circuit with Additional Bias Resistor
Figure 3. Typical NTC Thermistor Circuit
3558f
18
LTC3558
APPLICATIONS INFORMATION
USB and Wall Adapter Power
current. It is not necessary to perform any worst-case
power dissipation scenarios because the LTC3558 will
automatically reduce the charge current to maintain the
die temperature at approximately 105°C. However, the
approximate ambient temperature at which the thermal
feedback begins to protect the IC is:
Although the battery charger is designed to draw power
from a USB port to charge Li-Ion batteries, a wall adapter
can also be used. Figure 5 shows an example of how to
combine wall adapter and USB power inputs. A P-channel
MOSFET, MP1, is used to prevent back conduction into
the USB port when a wall adapter is present and Schottky
diode, D1, is used to prevent USB power loss through the
1k pull-down resistor.
TA = 105°C–PDθJA
T = 105°C– V – V
•IBAT •θJA
(
)
A
CC
BAT
Example: Consider an LTC3558 operating from a USB port
providing 500mA to a 3.5V Li-Ion battery. The ambient
temperatureabovewhichtheLTC3558willbegintoreduce
the 500mA charge current is approximately:
Typically, a wall adapter can supply significantly more
current than the 500mA-limited USB port. Therefore, an
N-channelMOSFET,MN1,andanextraprogramresistorare
used to increase the maximum charge current to 950mA
when the wall adapter is present.
T = 105°C – 5V – 3.5V • 500mA •68°C / W
(
) (
)
A
TA = 105°C – 0.75W •68°C / W = 105°C – 51°C
TA = 54°C
5V WALL
I
BAT
ADAPTER
BAT
BATTERY
CHARGER
V
CC
950mA I
CHG
D1
The LTC3558 can be used above 70°C, but the charge cur-
rentwillbereducedfrom500mA. Theapproximatecurrent
at a given ambient temperature can be calculated:
USB
POWER
MP1
500mA I
+
CHG
Li-Ion
BATTERY
PROG
1.65k
105°C– TA
MN1
1.74k
IBAT
=
1k
V – V
•θ
(
)
CC
BAT
JA
3558 F05
Using the previous example with an ambient tem-
perature of 88°C, the charge current will be reduced to
approximately:
Figure 5. Combining Wall Adapter and USB Power
105°C – 88°C
17°C
IBAT
=
=
Power Dissipation
5V – 3.5V •68°C / W 102°C / A
(
)
IBAT = 167mA
The conditions that cause the LTC3558 to reduce charge
current through thermal feedback can be approximated
by considering the power dissipated in the IC. For high
charge currents, the LTC3558 power dissipation is
approximately:
Furthermore, the voltage at the PROG pin will change
proportionally with the charge current as discussed in
the Programming Charge Current section.
It is important to remember that LTC3558 applications do
notneedtobedesignedforworst-casethermalconditions
since the IC will automatically reduce power dissipation
when the junction temperature reaches approximately
105°C.
P = V – V
•I
BAT
(
)
D
CC
BAT
where P is the power dissipated, V is the input supply
D
CC
voltage, V is the battery voltage, and I is the charge
BAT
BAT
3558f
19
LTC3558
APPLICATIONS INFORMATION
Battery Charger Stability Considerations
Average,ratherthaninstantaneous,batterycurrentmaybe
of interest to the user. For example, if a switching power
supply operating in low-current mode is connected in
parallel with the battery, the average current being pulled
out of the BAT pin is typically of more interest than the
instantaneous current pulses. In such a case, a simple RC
filtercanbeusedonthePROGpintomeasuretheaverage
battery current as shown in Figure 6. A 10k resistor has
been added between the PROG pin and the filter capacitor
to ensure stability.
TheLTC3558batterychargercontainstwocontrolloops:the
constant-voltageandconstant-currentloops.Theconstant-
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 1.5μF from BAT
to GND. Furthermore, a 4.7μF capacitor with a 0.2Ω to 1Ω
series resistor from BAT to GND is required to keep ripple
voltage low when the battery is disconnected.
USB Inrush Limiting
High value capacitors with very low ESR (especially
ceramic) reduce the constant-voltage loop phase margin,
possibly resulting in instability. Ceramic capacitors up to
22μF may be used in parallel with a battery, but larger
ceramics should be decoupled with 0.2Ω to 1Ω of series
resistance.
When a USB cable is plugged into a portable product,
the inductance of the cable and the high-Q ceramic input
capacitorformanL-Cresonantcircuit.Ifthereisnotmuch
impedance in the cable, it is possible for the voltage at
the input of the product to reach as high as twice the
USB voltage (~10V) before it settles out. In fact, due to
the high voltage coefficient of many ceramic capacitors
(a nonlinearity), the voltage may even exceed twice the
USB voltage. To prevent excessive voltage from damag-
ing the LTC3558 during a hot insertion, the soft connect
circuit in Figure 7 can be employed.
In constant-current mode, the PROG pin is in the feedback
loop,notthebattery.Becauseoftheadditionalpolecreated
bythePROGpincapacitance,capacitanceonthispinmust
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 maximum allowed program resis-
tor. The pole frequency at the PROG pin should be kept
above 100kHz. Therefore, if the PROG pin is loaded with a
In the circuit of Figure 7, capacitor C1 holds MP1 off
when the cable is first connected. Eventually C1 begins
to charge up to the USB input voltage applying increasing
gate support to MP1. The long time constant of R1 and
C1 prevents the current from building up in the cable too
fast thus dampening out any resonant overshoot.
capacitance,C
,thefollowingequationshouldbeused
PROG
to calculate the maximum resistance value for R
:
PROG
1
RPROG
≤
2π •105 •CPROG
MP1
Si2333
V
CC
C1
100nF
LTC3558
5V USB
INPUT
CHARGE
10k
C2
10μF
LTC3558
USB CABLE
CURRENT
MONITOR
CIRCUITRY
PROG
R1
40k
GND
R
C
FILTER
PROG
GND
3558 F06
3558 F07
Figure 6. Isolated Capacitive Load on PROG Pin and Filtering
Figure 7. USB Soft Connect Circuit
3558f
20
LTC3558
APPLICATIONS INFORMATION
Buck Switching Regulator General Information
Buck Switching Regulator
Output Voltage Programming
The LTC3558 contains a 2.25MHz constant-frequency
current mode buck switching regulator that can provide
up to 400mA. The switcher can be programmed for a
minimumoutputvoltageof0.8Vandcanbeusedtopower
a microcontroller core, microcontroller I/O, memory or
other logic circuitry. The regulator supports 100% duty
cycle operation (dropout mode) when the input voltage
drops very close to the output voltage and is also capable
of operating in Burst Mode operation for highest efficien-
ciesatlightloads(BurstModeoperationispinselectable).
The buck switching regulator also includes soft-start to
limit inrush current when powering on, short-circuit cur-
rent protection, and switch node slew limiting circuitry to
reduce radiated EMI.
The buck switching regulator can be programmed for
output voltages greater than 0.8V. The output voltage
for the buck switching regulator is programmed using a
resistor divider from the switching regulator output con-
nected to its feedback pin (FB1), as shown in Figure 8,
such that:
V
= 0.8(1 + R1/R2)
OUT
Typical values for R1 are in the range of 40k to 1M. The
capacitor CFB cancels the pole created by feedback re-
sistors and the input capacitance of the FB pin and also
helps to improve transient response for output voltages
much greater than 0.8V. A variety of capacitor sizes can
be used for CFB but a value of 10pF is recommended for
most applications. Experimentation with capacitor sizes
between 2pF and 22pF may yield improved transient
response if so desired by the user.
A MODE pin sets the buck switching regulator in Burst
Modeoperationorpulseskipoperatingmode. Theregula-
tor is enabled individually through its enable pin. The buck
regulator input supply (PV ) should be connected to the
IN1
Buck Switching Regulator Operating Modes
battery pin (BAT) and PV . This allows the undervoltage
IN2
lockoutcircuitontheBATpintodisablethebuckregulators
when the BAT voltage drops below 2.45V. Do not drive the
buck switching regulator from a voltage other than BAT.
The buck switching regulator includes two possible oper-
ating modes to meet the noise/power needs of a variety
of applications.
A 10μF decoupling capacitor from the PV pin to GND
IN1
In pulse skip mode, an internal latch is set at the start of
every cycle, which turns on the main P-channel MOSFET
is recommended.
P
VIN
EN
MP
SW
PWM
CONTROL
L
V
OUT
C
O
C
FB
MODE
MN
R1
R2
FB
0.8V
GND
3558 F08
Figure 8. Buck Converter Application Circuit
3558f
21
LTC3558
APPLICATIONS INFORMATION
switch.Duringeachcycle,acurrentcomparatorcompares
thepeakinductorcurrenttotheoutputofanerroramplifier.
The output of the current comparator resets the internal
latch,whichcausesthemainP-channelMOSFETswitchto
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 buck switching regulator requiring only a
single ceramic output capacitor for stability. At light loads
in pulse skip 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 (SW1)
goes high impedance and the switch node voltage will
“ring”. This is discontinuous operation, and is normal be-
haviorforaswitchingregulator. Atverylightloadsinpulse
skipmode, thebuckswitchingregulatorwillautomatically
skip pulses as needed to maintain output regulation. At
powered down, helping conserve battery power. When
the output voltage drops below a pre-determined value,
the buck switching regulator circuitry is powered on and
anotherburstcyclebegins.Thesleeptimedecreasesasthe
loadcurrentincreases.Beyondacertainloadcurrentpoint
(about 1/4 rated output load current) the buck switching
regulator will switch to a low noise constant-frequency
PWM mode of operation, much the same as pulse skip
operation at high loads. For applications that can tolerate
some output ripple at low output currents, Burst Mode
operation provides better efficiency than pulse skip at
light loads.
The buck switching regulator allows mode transition on-
the-fly,providingseamlesstransitionbetweenmodeseven
under load. This allows the user to switch back and forth
between modes to reduce output ripple or increase low
current efficiency as needed. Burst Mode operation is set
by driving the MODE pin high, while pulse skip mode is
achieved by driving the MODE pin low.
Buck Switching Regulator in Shutdown
high duty cycle (V
> PV /2) in pulse skip mode, it is
OUT
IN1
The buck switching regulator is in shutdown when not
enabledforoperation.Inshutdown,allcircuitryinthebuck
switchingregulatorisdisconnectedfromtheregulatorinput
supply, leaving only a few nanoamps of leakage pulled to
ground through a 13k resistor on the switch (SW1) pin
when in shutdown.
possible for the inductor current to reverse causing the
buck converter to switch continuously. Regulation and
low noise operation are maintained but the input supply
current will increase to a couple mA due to the continuous
gate switching.
During Burst Mode operation, the buck switching regula-
tor automatically switches between fixed frequency PWM
operation and hysteretic control as a function of the load
current.Atlightloadsthebuckswitchingregulatorcontrols
the inductor current directly and use a hysteretic control
loop to minimize both noise and switching losses. During
Burst Mode operation, the output capacitor is charged to a
voltage slightly higher than the regulation point. The buck
switching regulator then goes into sleep mode, during
which the output capacitor provides the load current. In
sleep mode, most of the switching regulator’s circuitry is
Buck Switching Regulator Dropout Operation
It is possible for the buck switching regulator’s input volt-
age to approach its programmed output voltage (e.g., a
battery voltage of 3.4V with a programmed output voltage
of 3.3V). When this happens, the PMOS switch duty cycle
increasesuntilitisturnedoncontinuouslyat100%.Inthis
dropoutcondition,therespectiveoutputvoltageequalsthe
regulator’s input voltage minus the voltage drops across
the internal P-channel MOSFET and the inductor.
3558f
22
LTC3558
APPLICATIONS INFORMATION
Buck Switching Regulator Soft-Start Operation
Buck Switching Regulator Inductor Selection
Soft-startisaccomplishedbygraduallyincreasingthepeak
inductorcurrentforeachswitchingregulatorovera500μs
period. This allows an output to rise slowly, helping mini-
mize the battery in-rush current required to charge up the
regulator’soutputcapacitor.Asoft-startcycleoccurswhen
the buck switcher first turns on, or after a fault condition
has occurred (thermal shutdown or UVLO). A soft-start
cycle is not triggered by changing operating modes using
theMODEpin.Thisallowsseamlessoutputoperationwhen
transitioning between operating modes.
The buck switching regulator is designed to work with
inductors in the range of 2.2μH to 10μH, but for most
applications a 4.7μH inductor is suggested. Larger value
inductors reduce ripple current which improves output
ripple voltage. Lower value inductors result in higher
ripple current which improves transient response time.
To maximize efficiency, choose an inductor with a low DC
resistance.Fora1.2Voutputefficiencyisreducedabout2%
forevery100mΩseriesresistanceat400mAloadcurrent,
andabout2%forevery300mΩseriesresistanceat100mA
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 buck regulators.
Buck Switching Regulator
Switching Slew Rate Control
The buck switching regulator contains circuitry to limit
the slew rate of the switch node (SW1). This circuitry is
designed to transition the switch node over a period of a
couple of nanoseconds, significantly reducing radiated
EMI and conducted supply noise while maintaining high
efficiency.
Differentcorematerialsandshapeswillchangethesize/cur-
rentandprice/currentrelationshipofaninductor.Toroidor
shieldedpotcoresinferriteorpermalloymaterialsaresmall
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 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 buck regulator requires to operate.
Buck Switching Regulator Low Supply Operation
An undervoltage lockout (UVLO) circuit on PV shuts
IN1
downthestep-downswitchingregulatorswhenBATdrops
below2.45V.ThisUVLOpreventsthebuckswitchingregu-
lator from operating at low supply voltages where loss of
regulation or other undesirable operation may occur.
The inductor value also has an effect on Burst Mode
operation. Lower inductor values will cause Burst Mode
switching frequency to increase.
3558f
23
LTC3558
APPLICATIONS INFORMATION
Table 2 shows several inductors that work well with the
LTC3558 buck switching regulator. 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.
for most applications. For good transient response and
stability the output capacitor should retain at least 4μF
of capacitance over operating temperature and bias volt-
age.Thebuckswitchingregulatorinputsupplyshouldbe
bypassed with a 10μF capacitor. Consult manufacturer
for detailed information on their selection and specifica-
tions of ceramic capacitors. Many manufacturers now
offer very thin (< 1mm tall) ceramic capacitors ideal for
use in height-restricted designs. Table 3 shows a list of
several ceramic capacitor manufacturers.
Buck Switching Regulator
Input/Output Capacitor Selection
LowESR(equivalentseriesresistance)ceramiccapacitors
should be used at switching regulator outputs as well as
the switching regulator input supply. Ceramic capacitor
dielectrics are a compromise between high dielectric
constant and stability versus temperature and versus
DC bias voltage. The X5R/X7R dielectrics offer the best
compromisewithhighdielectricconstantandacceptable
performance over temperature and under bias. Do not
use Y5V dielectrics. A 10μF output capacitor is sufficient
Table 3: Recommended Ceramic Capacitor Manufacturers
AVX
Murata
(803) 448-9411
(714) 852-2001
(408) 537-4150
(888) 835-6646
www.avxcorp.com
www.murata.com
www.t-yuden.com
www.tdk.com
Taiyo Yuden
TDK
Table 2. Recommended Inductors for Buck Switching Regulators
L
(μH)
MAX I
(A)
MAX DCR
(mΩ)
SIZE IN mm
(L × W × H)
DC
INDUCTOR TYPE
MANUFACTURER
DE2818C
DE2812C
4.7
4.7
1.25
1.15
72*
130*
Toko
www.toko.com
3 × 2.8 × 1.8
3 × 2.8 × 1.2
CDRH3D16
4.7
0.9
110
Sumida
www.sumida.com
4 × 4 × 1.8
SD3118
SD3112
4.7
4.7
1.3
0.8
162
246
Cooper
www.cooperet.com
3.1 × 3.1 × 1.8
3.1 × 3.1 × 1.2
LPS3015
4.7
1.1
200
Coilcraft
www.coilcraft.com
3 × 3 × 1.5
*Typical DCR
3558f
24
LTC3558
APPLICATIONS INFORMATION
Buck-Boost Switching Regulator
the converter will operate in four-switch mode. While
operating in four-switch mode, switches turn on as per
the following sequence: switches A and D → switches A
and C → switches B and D → switches A and D.
The LTC3558 contains a 2.25MHz constant-frequency,
voltage mode, buck-boost switching regulator. The regu-
lator provides up to 400mA of output load current. The
buck-boost switching regulator can be programmed for a
minimumoutputvoltageof2.75Vandcanbeusedtopower
a microcontroller core, microcontroller I/O, memory, disk
drive, or other logic circuitry. To suit a variety of applica-
tions, different mode functions allow the user to trade off
noise for efficiency. Two modes are available to control the
operationofthebuck-boostregulator.Atmoderatetoheavy
loads, the constant-frequency PWM mode provides the
leastnoiseswitchingsolution.Atlighterloads,BurstMode
operationmaybeselected. Regulationismaintainedbyan
error amplifier that compares the divided output voltage
with a reference and adjusts the compensation voltage
accordinglyuntiltheFB2voltagehasstabilizedat0.8V.The
buck-boost switching regulator also includes soft-start to
limit inrush current and voltage overshoot when powering
on, short-circuit current protection, and switch node slew
limiting circuitry for reduced radiated EMI.
Buck-Boost Regulator Burst Mode Operation
In Burst Mode operation, the switching regulator uses a
hystereticfeedbackvoltagealgorithmtocontroltheoutput
voltage. By limiting FET switching and using a hysteretic
control loop switching losses are greatly reduced. In
this mode, output current is limited to 50mA. While in
Burst Mode operation, the output capacitor is charged
to a voltage slightly higher than the regulation point. The
buck-boost converter then goes into a SLEEP state, dur-
ing which the output capacitor provides the load current.
The output capacitor is charged by charging the inductor
until the input current reaches 250mA typical, and then
discharging the inductor until the reverse current reaches
0mA typical. This process of bursting current is repeated
until the feedback voltage has charged to the reference
voltage plus 6mV (806mV typical). In the SLEEP state,
most of the regulator’s circuitry is powered down, helping
to conserve battery power. When the feedback voltage
drops below the reference voltage minus 6mV (794mV
typical), the switching regulator circuitry is powered on
and another burst cycle begins. The duration for which the
regulator operates in SLEEP depends on the load current
and output capacitor value. The SLEEP time decreases
as the load current increases. The maximum deliverable
load current in Burst Mode operation is 50mA typical.
The buck-boost regulator may not enter SLEEP if the load
current is greater than 50mA. If the load current increases
beyond this point while in Burst Mode operation, the out-
put may lose regulation. Burst Mode operation provides a
significant improvement in efficiency at light loads at the
expense of higher output ripple when compared to PWM
mode. For many noise-sensitive systems, Burst Mode
operation might be undesirable at certain times (i.e., dur-
ing a transmit or receive cycle of a wireless device), but
highly desirable at others (i.e., when the device is in low
power standby mode).
Buck-Boost Regulator PWM Operating Mode
In PWM mode, the voltage seen at the feedback node is
compared to a 0.8V reference. From the feedback voltage,
an error amplifier generates an error signal seen at the
V
C2
pin. This error signal controls PWM waveforms that
modulate switches A (input PMOS), B (input NMOS), C
(output NMOS), and D (output PMOS). Switches A and
B operate synchronously, as do switches C and D. If the
input voltage is significantly greater than the programmed
output voltage, then the regulator will operate in buck
mode. In this case, switches A and B will be modulated,
withswitchDalwayson(andswitchCalwaysoff), tostep-
down the input voltage to the programmed output. If the
input voltage is significantly less than the programmed
output voltage, then the converter will operate in boost
mode. In this case, switches C and D are modulated, with
switch A always on (and switch B always off), to step up
the input voltage to the programmed output. If the input
voltage is close to the programmed output voltage, then
3558f
25
LTC3558
APPLICATIONS INFORMATION
Buck-Boost Switching Regulator Output Voltage
Programming
The output filter zero is given by:
1
fFILTER_ZERO
=
Hz
The buck-boost switching regulator can be programmed
foroutputvoltagesgreaterthan2.75Vandlessthan5.45V.
To program the output voltage, a resistor divider is con-
2• π •RESR •COUT
where R
is the capacitor equivalent series resistance.
ESR
nected between V
and the feedback node (FB2) as
OUT2
A troublesome feature in boost mode is the right-half
plane zero (RHP), and is given by:
shown in Figure 9. The output voltage is given by V
= 0.8(1 + R1/R2).
OUT2
2
PV
IN2
fRHPZ
=
Hz
LTC3558
2• π •IOUT •L • VOUT2
V
OUT2
R1
R2
The loop gain is typically rolled off before the RHP zero
frequency.
FB2
AsimpleTypeIcompensationnetwork,asshowninFigure
10, can be incorporated to stabilize the loop, but at the
costofreducedbandwidthandslowertransientresponse.
To ensure proper phase margin, the loop requires to be
crossed over a decade before the LC double pole.
3558 F09
Figure 9. Programming the Buck-Boost Output Voltage Requires
a Resistor Divider Connected Between VOUT2 and FB2
The unity-gain frequency of the error amplifier with the
Type I compensation is given by:
Closing the Feedback Loop
TheLTC3558incorporatesvoltagemodePWMcontrol.The
control to output gain varies with operation region (buck,
boost, buck-boost), but is usually no greater than 20. The
output filter exhibits a double pole response given by:
1
fUG
=
Hz
2• π •R1•CP1
1
fFILTER_POLE
=
Hz
2• π • L •COUT
where C
is the output filter capacitor.
OUT
V
OUT2
R1
0.8V
FB2
+
–
ERROR
AMP
C
R2
P1
V
C2
3558 F10
Figure 10. Error Amplifier with Type I Compensation
3558f
26
LTC3558
APPLICATIONS INFORMATION
Mostapplicationsdemandanimprovedtransientresponse
toallowasmalleroutputfiltercapacitor.Toachieveahigher
bandwidth, Type III compensation is required. Two zeros
are required to compensate for the double-pole response.
at the filter double pole. If they are placed at too low of a
frequency, theywillintroducetoomuchgaintothesystem
and the crossover frequency will be too high. The two high
frequency poles should be placed such that the system
crosses unity gain during the phase bump introduced
by the zeros and before the boost right-half plane zero
and such that the compensator bandwidth is less than
the bandwidth of the error amp (typically 900kHz). If the
gain of the compensation network is ever greater than
the gain of the error amplifier, then the error amplifier no
longer acts as an ideal op amp, and another pole will be
introduced at the same point.
Type III compensation also reduces any V
overshoot
OUT2
seen during a start-up condition. A Type III compensa-
tion circuit is shown in Figure 11 and yields the following
transfer function:
VC2
1
=
VOUT2 R1(C1+ C2)
(1+ sR2C2)[1+ s(R1+ R3)C3]
•
s 1+ sR2(C1||C2) (1+ sR3C3)
⎡
⎤
⎣
⎦
Recommended Type III compensation components for a
3.3V output are:
A Type III compensation network attempts to introduce
a phase bump at a higher frequency than the LC double
pole. This allows the system to cross unity gain after the
LC double pole, and achieve a higher bandwidth. While
attempting to cross over after the LC double pole, the
system must still cross over before the boost right-half
plane zero. If unity gain is not reached sufficiently before
the right-half plane zero, then the –180° of phase lag from
the LC double pole combined with the –90° of phase lag
from the right-half plane zero will result in negating the
phase bump of the compensator.
R1: 324kΩ
R : 105kΩ
FB
C1: 10pF
R2: 15kΩ
C2: 330pF
R3: 121kΩ
C3: 33pF
C
L
: 22ꢀF
OUT
The compensator zeros should be placed either before
or only slightly after the LC double pole such that their
positive phase contributions offset the –180° that occurs
: 2.2ꢀH
OUT
V
OUT2
R3
C3
0.8V
+
R1
ERROR
AMP
FB2
–
R
C2
FB
V
C2
R2
C1
3558 F11
Figure 11. Error Amplifier with Type III Compensation
3558f
27
LTC3558
APPLICATIONS INFORMATION
Input Current Limit
Buck-Boost Switching Regulator Inductor Selection
The buck-boost switching regulator is designed to work
with inductors in the range of 1μH to 5μH. For most
applications, a 2.2μH inductor will suffice. Larger value
inductors reduce ripple current which improves output
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 and 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
current should be rated to handle up to the peak current
specified for the buck-boost regulator.
TheinputcurrentlimitcomparatorwillshuttheinputPMOS
switchoffoncecurrentexceeds700mAtypical. Beforethe
switchcurrentlimit,theaveragecurrentlimitamp(620mA
typical) will source current into the feedback pin to drop
the output voltage. The input current limit also protects
against a short-circuit condition at the V
pin.
OUT2
Reverse Current Limit
The reverse current limit comparator will shut the output
PMOS switch off once current returning from the output
exceeds 450mA typical.
Output Overvoltage Protection
The inductor value also affects Burst Mode operation.
Lower inductor values will cause Burst Mode switching
frequencies to increase.
Ifthefeedbacknodewereinadvertentlyshortedtoground,
then the output would increase indefinitely with the maxi-
mum current that could be sourced from the input supply.
The buck-boost regulator protects against this by shutting
off the input PMOS if the output voltage exceeds a 5.75V
maximum.
Differentcorematerialsandshapeswillchangethesize/cur-
rent and price/current relationship of an inductor. Toroid
or shielded pot cores in ferrite or permalloy materials
are small and do not radiate much energy, but 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.
Buck-Boost Regulator Soft-Start Operation
Soft-start is accomplished by gradually increasing the
reference voltage over a 500μs typical period. A soft-
start cycle occurs whenever the buck-boost 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 and
PWM mode operation.
Table 4 shows some inductors that work well with the
buck-boost regulator. These inductors offer a good com-
promise in current rating, DCR and physical size. Consult
each manufacturer for detailed information on their entire
selection of inductors.
Table 4. Recommended Inductors for the Buck-Boost Switching Regulator.
L
(μH)
MAX I
(A)
MAX DCR
(mΩ)
SIZE IN mm
(L × W × H)
DC
INDUCTOR TYPE
MANUFACTURER
DB3018C
D312C
DE2812C
DE2812C
2.4
2.2
2
1.31
1.14
1.4
80
140
81
Toko
www.toko.com
3.8 × 3.8 × 1.4
3.6 × 3.6 × 1.2
3 × 3.2 × 1.2
3 × 3.2 × 1.2
2.7
1.2
87
CDRH3D16
2.2
1.2
72
Sumida
www.sumida.com
4 × 4 × 1.8
SD12
2.2
1.8
74
Cooper
www.cooperet.com
5.2 × 5.2 × 1.2
*Typical DCR
3558f
28
LTC3558
APPLICATIONS INFORMATION
Buck-Boost Switching Regulator Input/Output
Capacitor Selection
PCB Layout Considerations
In order to deliver maximum charge current under all
conditions, it is critical that the backside of the LTC3558
be soldered to the PC board ground.
LowESR(equivalentseriesresistance)ceramiccapacitors
should be used at both the buck-boost regulator input
(PV )andtheoutput(V
).Itisrecommendedthatthe
IN2
OUT2
The LTC3558 has dual switching regulators. As with all
switching regulators, care must be taken while laying out
aPCboardandplacingcomponents. Theinputdecoupling
capacitors, the output capacitor and the inductors must all
be placed as close to the pins as possible and on the same
side of the board as the LTC3558. All connections must
also be made on the same layer. Place a local unbroken
ground plane below these components. Avoid routing
noisy high frequency lines such as those that connect to
switch pins over or parallel to lines that drive high imped-
ance inputs.
inputbebypassedwitha10μFcapacitor.Theoutputshould
be bypassed with at least a 10μF capacitor if using Type I
compensation and 22μF if using Type III compensation.
The same selection criteria apply for the buck-boost
regulator input and output capacitors as described in the
Buck Switching Regulator Input/Output Capacitor Selec-
tion section.
3558f
29
LTC3558
TYPICAL APPLICATIONS
UP TO 500mA
USB
V
BAT
CC
SINGLE
Li-lon CELL
(2.7V TO 4.2V)
(4.3V TO 5.5V)
+
10μF
PV
IN1
IN2
110k
OR AC ADAPTER
1
PV
NTC
10μF
4.7μF
28.7K
100k (NTC)
NTH50603NO1
LTC3558
510Ω
1.8V AT 400mA
10pF
4.7μH
SW1
CHRG
PROG
10μF
806k
1.74k
FB1
649k
SUSP
HPWR
EN1
SWAB2
2.2μH
DIGITAL
CONTROL
3.3V AT 400mA
SWCD2
V
OUT2
EN2
619k
200k
10μF
MODE
FB2
15k
150pF
GND2
(EXPOSED
PAD)
V
C2
GND
3558 TA02
Figure 12. Li-Ion to 3.3V at 400mA, 1.8V at 400mA and USB-Compatible Battery Charger
As shown in Figure 12, the LTC3558 can be operated
with no battery connected to the BAT pin. A 1Ω resistor
in series with a 4.7μF capacitor at the BAT pin ensures
in Figure 13. CHRG has a LED to provide a user with a
visual indication of battery charge status. The buck-boost
regulator starts up only after V is up to approximately
0.7V. This provides a sequencing function which may be
desirableinapplicationswhereamicroprocessorneedsto
bepoweredupbeforeperipherals.ATypeIIIcompensation
networkimprovesthetransientresponseofthebuck-boost
switching regulator.
OUT1
battery charger stability. 10μF V decoupling capacitors
CC
arerequiredforproperoperationoftheDC/DCconverters.
A three-resistor bias network for NTC sets hot and cold
trip points at approximately 55°C and 0°C.
The battery can be charged with up to 950mA of charge
current when powered from a 5V wall adaptor, as shown
3558f
30
LTC3558
PACKAGE DESCRIPTION
UD Package
20-Lead Plastic QFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1720 Rev A)
0.70 ±0.05
3.50 ± 0.05
(4 SIDES)
1.65 ± 0.05
2.10 ± 0.05
PACKAGE
OUTLINE
0.20 ±0.05
0.40 BSC
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
BOTTOM VIEW—EXPOSED PAD
PIN 1 NOTCH
R = 0.20 TYP
OR 0.25 × 45°
CHAMFER
R = 0.115
TYP
0.75 ± 0.05
3.00 ± 0.10
(4 SIDES)
R = 0.05
TYP
19 20
PIN 1
TOP MARK
(NOTE 6)
0.40 ± 0.10
1
2
1.65 ± 0.10
(4-SIDES)
(UD20) QFN 0306 REV A
0.200 REF
0.20 ± 0.05
0.00 – 0.05
0.40 BSC
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
3558f
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.
31
LTC3558
TYPICAL APPLICATIONS
UP TO 950mA
4.7μH
5V WALL
ADAPTER
V
BAT
CC
SINGLE
Li-lon CELL
(2.7V TO 4.2V)
+
1μF
PV
IN1
100k
PV
10μF
IN2
NTC
1.2V AT 400mA
10pF
LTC3558
510Ω
100k (NTC)
SW1
10μF
324k
CHRG
PROG
FB1
887Ω
SWAB2
649k
SUSP
HPWR
MODE
EN1
2.2μH
DIGITAL
CONTROL
3.3V AT 400mA
SWCD2
V
OUT2
121k
33pF
22μF
10pF
324k
105k
EN2
FB2
15k
GND2
(EXPOSED
PAD)
330pF
GND
V
C2
Figure 13. Battery Charger Can Charge a Battery with Up to 950mA When Powered From a Wall Adapter
RELATED PARTS
PART NUMBER DESCRIPTION
COMMENTS
LTC3550
Dual Input USB/AC Adapter Li-Ion Battery Synchronous Buck Converter, Efficiency: 93%, Adjustable Output at 600mA, Charge Current:
Charger with Adjustable Output 600mA
Buck Converter
950mA Programmable, USB Compatible, Automatic Input Power Detection
and Selection
LTC3552
Standalone Linear Li-Ion Battery Charger
Synchronous Buck Converter, Efficiency: >90%, Adjustable Outputs at 800mA and
with Adjustable Output Dual Synchronous 400mA, Charge Current Programmable Up to 950mA, USB Compatible, 5mm × 3mm
Buck Converter
DFN-16 Package
LTC3552-1
LTC3455
Standalone Linear Li-Ion Battery Charger
with Dual Synchronous Buck Converter
Synchronous Buck Converter, Efficiency: >90%, Outputs 1.8V at 800mA and 1.575 at
400mA, Charge Current Programmable up to 950mA, USB Compatible
Dual DC/DC Converter with USB Power
Manager and Li-Ion Battery Charger
Seamless Transition Between Input Power Sources: Li-Ion Battery, USB and 5V Wall
Adapter, Two High Efficiency DC/DC Converters: Up to 96%, Full Featured Li-Ion Battery
Charger with Accurate USB Current Limiting (500mA/100mA) Pin-Selectable Burst Mode
Operation, Hot SwapTM Output for SDIO and Memory Cards, 4mm × 4mm QFN-24 Package
LTC3456
2-Cell, Multi-Output DC/DC Converter with Seamless Transition Between 2-Cell Battery, USB and AC Wall Adapter Input Power Sources,
USB Power Manager
Main Output: Fixed 3.3V Output, Core Output: Adjustable from 0.8V to V
, Hot Swap
BATT(MIN)
Output for Memory Cards, Power Supply Sequencing: Main and Hot Swap Accurate USB
Current Limiting, High Frequency Operation: 1MHz, High Efficiency: Up to 92%, 4mm ×
4mm QFN-24 Package
LTC3559
LTC4080
USB Charger with Dual Buck Regulators
Adjustable, Synchronous Buck Converters, Efficiency >90%, Outputs: Down to 0.8V at
400mA Each, Charge Current Programmable Up to 950mA, USB-Compatible, 3mm × 3mm
QFN-16 Package
500mA Standalone Charger with 300mA
Synchronous Buck
Charges Single-Cell Li-Ion Batteries, Timer Termination + C/10, Thermal Regulation, Buck
Output: 0.8V to V , Buck Input V : 2.7V to 5.5V, 3mm × 3mm DFN-10 Package
BAT
IN
Hot Swap is a trademark of Linear Technology Corporation.
3558f
LT 0408 • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
32
●
●
© LINEAR TECHNOLOGY CORPORATION 2008
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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