LTC3550-1 [Linear]
Dual Input USB/AC Adapter Li-Ion Battery Charger with 600mA Buck Converter; 双输入USB / AC适配器锂离子电池充电器的600mA buck变换器
| 型号： | LTC3550-1 |
| 厂家： | 
Linear |
| 描述： | Dual Input USB/AC Adapter Li-Ion Battery Charger with 600mA Buck Converter |
| 文件： | 总24页 (文件大小：344K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC3550-1
Dual Input USB/AC Adapter
Li-Ion Battery Charger with
600mA Buck Converter
U
DESCRIPTIO
FEATURES
The LTC®3550-1 is a standalone linear charger with a
600mA monolithic synchronous buck converter. It is
capable of charging a single-cell Li-Ion battery from both
wall adapter and USB inputs. The charger automatically
selects the appropriate power source for charging.
■
Charges Single-Cell Li-Ion Batteries from Wall
Adapter and USB Inputs
■
Automatic Input Power Detection and Selection
■
Charge Current Programmable Up to 950mA from
Wall Adapter Input
■
High Efficiency 600mA Synchronous DC/DC
Internal thermal feedback regulates the battery charge
currenttomaintainaconstantdietemperatureduringhigh
power operation or high ambient temperature conditions.
The float voltage is fixed at 4.2V and the charge currents
are programmed with external resistors. The LTC3550-1
terminatesthechargecyclewhenthechargecurrentdrops
below the programmed termination threshold after the
final float voltage is reached. With power applied to both
inputs, the LTC3550-1 can be put into shutdown mode
reducing the DCIN supply current to 20μA, the USBIN
supply current to 10μA, and the battery drain current to
less than 2μA.
Converter
■
No External MOSFET, Sense Resistor or Blocking
Diode Needed
■
Thermal Regulation Maximizes Charge Rate Without
Risk of Overheating*
■
Preset Charge Voltage with 0.6ꢀ Accuracy
■
Programmable Charge Current Termination
■
1.5MHz Constant Frequency Operation (Step-Down
Converter)
■
18μA USB Suspend Current in Shutdown
■
Independent “Power Present” Status Outputs
■
Charge Status Output
Automatic Recharge
■
■
The synchronous buck converter generates a fixed output
voltage of 1.875V. The switching frequency is internally
set at 1.5MHz, allowing the use of small surface mount
inductors and capacitors.
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
*Protected by U.S. patents, includng 6522118, 6700364, 6580258, 5481178, 6304066,
6127815, 6498466, 6611131
Available in a Thermally Enhanced, Low Profile
(0.75mm) 16-Lead (5mm x 3mm) DFN Package
U
APPLICATIO S
■
Cellular Telephones
U
TYPICAL APPLICATIO
Complete Charge Cycle (1100mA Battery)
1000
800
600
400
200
0
4.2
4.0
3.8
3.6
3.4
Dual Input Battery Charger and DC/DC Converter
LTC3550-1
RUN SW
2.2µH
V
OUT
1.875V
600mA
WALL
CONSTANT VOLTAGE
USBIN = 5V
C
OUT
ADAPTER
DCIN
USBIN
IUSB
IDC
V
OUT
10µF
800mA (WALL)
500mA (USB)
CER
V
USB
PORT
CC
T
= 25°C
A
IDC
1µF
BAT
R
R
= 1.25k
= 2k
2k
1%
4.7µF
IUSB
ITERM
5.0
2.5
0
4.2V
+
1µF
GND
2k
1%
1.24k
1%
SINGLE-CELL
Li-Ion BATTERY
–2.5
3550-1 TA01
0
0.5
1.0
1.5
2.0
2.5
3.0
TIME (HR)
3550-1 TA02
35501f
1
LTC3550-1
W W U W
U
W
U
ABSOLUTE AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
(Note 1)
TOP VIEW
DCIN, USBIN.............................................. –0.3V to 10V
ENABLE, CHRG, PWR, USBPWR ............... –0.3V to 10V
BAT, IDC, IUSB, ITERM ................................ –0.3V to 7V
USBIN
IUSB
1
2
3
4
5
6
7
8
16 DCIN
15 BAT
ITERM
PWR
14 IDC
V ............................................................... –0.3V to 6V
CC
RUN, V
13 USBPWR
12 ENABLE
11 RUN
10 SW
..................................................–0.3V to V
17
OUT
CC
CHRG
SW (DC)........................................–0.3V to (V + 0.3V)
CC
V
OUT
DCIN Pin Current (Note 2) ..........................................1A
USBIN Pin Current (Note 2) .................................700mA
BAT Pin Current (Note 2) ............................................1A
P-Channel SW Source Current (DC).....................800mA
N-Channel SW Source Current (DC) ....................800mA
Peak SW Sink and Source Current...........................1.3A
Operating Temperature Range (Note 3) ... –40°C to 85°C
Maximum Junction Temperature .......................... 125°C
Storage Temperature Range................... –65°C to 125°C
V
CC
GND
9
GND
DHC PACKAGE
16-LEAD (5mm × 3mm) PLASTIC DFN
T
JMAX
= 125°C, θ = 40°C (Note 4)
JA
EXPOSED PAD IS GROUND (PIN 17)
MUST BE SOLDERED TO PCB
ORDER PART NUMBER
PART MARKING
35501
LTC3550EDHC-1
Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T = 25°C. V
= 5V, V
= 5V, V = 3.6V unless otherwise noted.
USBIN CC
A
DCIN
SYMBOL
PARAMETER
CONDITIONS
MIN
4.3
4.3
2.5
0.4
1.2
0.3
TYP
MAX
8
UNITS
●
●
●
V
V
V
V
Wall Adapter Input Supply Voltage
USB Port Input Supply Voltage
Buck Regulator Input Supply Voltage
ENABLE Input Threshold Voltage
ENABLE Pulldown Resistance
RUN Threshold Voltage
V
V
DCIN
USBIN
CC
8
5.5
1.0
5
V
0.7
2
V
ENABLE
R
MΩ
V
ENABLE
RUN
●
●
V
1
1.5
1
I
RUN Leakage Current
0.01
0.35
0.35
0.35
µA
V
RUN
V
V
V
V
CHRG Output Low Voltage
PWR Output Low Voltage
I
I
I
= 5mA
= 5mA
0.6
0.6
0.6
4.3
CHRG
CHRG
V
PWR
PWR
USBPWR Output Low Voltage
DCIN Undervoltage Lockout Voltage
= 200µA
USBPWR
V
USBPWR
UVDC
From Low to High
Hysteresis
4.0
3.8
4.15
200
V
mV
V
USBIN Undervoltage Lockout Voltage
From Low to High
Hysteresis
3.95
200
4.1
V
mV
UVUSB
35501f
2
LTC3550-1
ELECTRICAL CHARACTERISTICS The
●
denotes the specifications which apply over the full operating
= 5V, V = 5V, V = 3.6V unless otherwise noted.
temperature range, otherwise specifications are at T = 25°C. V
A
DCIN
USBIN
CC
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
V
– V Lockout Threshold Voltage
V
V
from Low to High, V = 4.2V
140
20
180
50
220
80
mV
mV
ASD-DC
DCIN
BAT
DCIN
DCIN
BAT
from High to Low, V = 4.2V
BAT
V
V
– V Lockout Threshold
V
USBIN
V
USBIN
from Low to High, V = 4.2V
140
20
180
50
220
80
mV
mV
ASD-USB
USBIN
BAT
BAT
Voltage
from High to Low, V = 4.2V
BAT
Battery Charger
I
DCIN Supply Current
Charge Mode (Note 5)
Standby Mode
DCIN
●
●
R
= 10k
250
50
20
800
100
40
µA
µA
µA
IDC
Charge Terminated
ENABLE = 5V
Shutdown Mode
I
USBIN Supply Current
Charge Mode (Note 6)
Standby Mode
USBIN
●
●
R
= 10k, V
= 0V
DCIN
250
50
800
100
36
µA
µA
µA
µA
IUSB
Charge Terminated
Shutdown Mode
V
V
= 0V, ENABLE = 0V
18
DCIN
DCIN
Shutdown Mode
> V
10
20
USBIN
V
Regulated Output (Float) Voltage
I
I
= 1mA
4.175
4.158
4.2
4.2
4.225
4.242
V
V
FLOAT
BAT
BAT
= 1mA, 0°C < T < 85°C
A
I
BAT Pin Current
BAT
●
●
●
Constant-Current Mode
Constant-Current Mode
Constant-Current Mode
Standby Mode
R
R
R
= 1.25k
IUSB
= 10k or R
Charge Terminated
Charger Disabled
760
450
93
800
476
100
–3
840
500
107
–6
mA
mA
mA
µA
IDC
= 2.1k
= 10k
IUSB
IDC
Shutdown Mode
Sleep Mode
–1
–2
µA
DCIN = 0V, USBIN = 0V
Constant-Current Mode
Constant-Current Mode
1
2
µA
V
V
IDC Pin Regulated Voltage
0.95
0.95
1.0
1.0
1.05
1.05
V
V
IDC
IUSB Pin Regulated Voltage
IUSB
●
●
●
●
I
Charge Current Termination Threshold
R
ITERM
R
ITERM
R
ITERM
R
ITERM
= 1k
90
45
8.5
4
100
50
10
5
110
55
11.5
6
mA
mA
mA
mA
TERMINATE
= 2k
= 10k
= 20k
ΔV
Recharge Battery Threshold Voltage
Recharge Comparator Filter Time
Termination Comparator Filter Time
Soft-Start Time
V
V
– V
, 0°C < T < 85°C
65
3
100
6
135
9
mV
ms
ms
µs
RECHRG
FLOAT
RECHRG
A
t
t
t
from High to Low
RECHRG
BAT
BAT
I
I
Drops Below Termination Threshold
0.8
175
1.5
250
400
2.2
325
TERMINATE
SS
= 10ꢀ to 90ꢀ Full-Scale
BAT
R
Power FET On-Resistance (Between
DCIN and BAT)
mΩ
ON-DC
ON-USB
LIM
R
Power FET On-Resistance (Between
USBIN and BAT)
550
105
mΩ
T
Junction Temperature in Constant-
Temperature Mode
°C
Switching Regulator
●
●
V
Regulated Output Voltage
Output Voltage Line Regulation
Peak Inductor Current
I
= 100mA
1.819
0.75
1.875
0.04
1
1.931
0.4
V
ꢀ/V
A
OUT
OUT
ΔV
OUT
I
PK
V
= 3V, V = 1.7V
OUT
1.25
CC
V
Output Voltage Load Regulation
0.5
ꢀ
LOADREG
I
S
Input DC Bias Current
Active Mode
(Note 7)
V
OUT
V
OUT
V
RUN
= 1.7V, I
= 0A
LOAD
300
20
0.1
400
35
1
µA
µA
µA
LOAD
Sleep Mode
= 1.94V, I
= 0V, V = 5.5V
= 0A
Shutdown
CC
35501f
3
LTC3550-1
ELECTRICAL CHARACTERISTICS The
●
denotes the specifications which apply over the full operating
= 5V, V = 5V, V = 3.6V unless otherwise noted.
temperature range, otherwise specifications are at T = 25°C. V
A
DCIN
CONDITIONS
USBIN
CC
SYMBOL
PARAMETER
MIN
TYP
MAX
UNITS
f
Oscillator Frequency
V
OUT
V
OUT
= 100ꢀ
= 0V
1.2
1.5
210
1.8
MHz
kHz
OSC
Ω
Ω
R
R
R
R
of P-Channel FET
of N-Channel FET
0.4
PFET
NFET
LSW
DS(ON)
0.35
0.01
DS(ON)
I
SW Leakage Current
1
µA
Note 5: Supply Current includes IDC and ITERM pin current (approx-
imately 100μA each) but does not include any current delivered to the
battery through the BAT pin (approximately 100mA).
Note 6: Supply Current includes IUSB and ITERM pin current (approx-
imately 100μA each) but does not include any current delivered to the
battery through the BAT pin (approximately 100mA).
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 2: Guaranteed by long term current density limitations.
Note 3: The LTC3550E-1 is guaranteed to meet the performance
specifications from 0°C to 70°C. Specifications over the –40°C to 85°C
operating temperature range are assured by design, characterization and
correlation with statistical process controls.
Note 7: Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency.
Note 4: Failure to solder the exposed backside of the package to the PC
board will result in a thermal resistance much higher than 40°C/W. See
Thermal Considerations.
35501f
4
LTC3550-1
U W
TYPICAL PERFOR A CE CHARACTERISTICS
T = 25°C, unless otherwise noted.
A
Regulated Charger Output (Float)
Voltage vs Charge Current
Regulated Charger Output (Float)
Voltage vs Temperature
IDC Pin Voltage vs Temperature
(Constant-Current Mode)
4.220
4.215
4.210
4.205
4.200
4.195
4.190
4.185
4.180
1.008
1.006
1.004
1.002
1.000
0.998
0.996
0.994
0.992
4.26
4.24
4.22
4.20
4.18
4.16
4.14
4.12
4.10
V
= V
= 5V
USBIN
V
= V
= 5V
USBIN
DCIN
DCIN
V
= 8V
DCIN
V
= 4.3V
DCIN
R
= 1.25k
R
= R
= 2k
IUSB
IDC
IDC
75
75
–50
–25
0
25
50
100
–50
–25
0
25
50
100
200
0
100
300 400 500 600 700 800
TEMPERATURE (°C)
TEMPERATURE (°C)
CHARGE CURRENT (mA)
3550-1 G02
3550-1 G03
3550-1 G01
IUSB Pin Voltage vs Temperature
(Constant-Current Mode)
Charge Current
vs IUSB Pin Voltage
Charge Current vs IDC Pin Voltage
900
800
700
600
500
400
300
200
100
0
900
800
700
600
500
400
300
200
100
0
1.008
1.006
1.004
1.002
1.000
0.998
0.996
0.994
0.992
V
= 5V
V
= 5V
USBIN
DCIN
R
= 1.25k
R
= 1.25k
= 2k
IDC
IUSB
R
R
= 2k
IUSB
IDC
V
= 8V
USBIN
V
= 4.3V
USBIN
R
= 10k
R
= 10k
IUSB
IDC
75
–50
–25
0
25
50
100
0
0.2
0.4
0.6
(V)
1.0
1.2
0
0.2
0.4
0.6
1.0
1.2
0.8
0.8
TEMPERATURE (°C)
V
V
(V)
IDC
IUSB
3550-1 G04
3550-1 G06
3550-1 G05
PWR Pin I-V Curve
CHRG Pin I-V Curve
USBPWR Pin I-V Curve
35
30
25
20
15
10
5
6
5
4
3
2
1
0
35
30
25
20
15
10
5
V
= V
= 5V
V
V
= 5V
= 0V
V
= V
= 5V
USBIN
DCIN
USBIN
DCIN
USBIN
DCIN
T
A
= –40°C
= 25°C
T
A
= –40°C
= 25°C
T
= –40°C
A
T
T
A
A
T
= 25°C
= 90°C
A
A
T
= 90°C
A
T
= 90°C
A
T
0
0
4
6
7
0
1
2
3
5
4
6
7
0
1
2
3
5
4
6
7
0
1
2
3
5
V
(V)
CHRG
V
(V)
V
(V)
USBPWR
PWR
3550-1 G08
3550-1 G09
3550-1 G07
35501f
5
LTC3550-1
U W
TYPICAL PERFOR A CE CHARACTERISTICS
T = 25°C, unless otherwise noted.
A
Charge Current
vs Ambient Temperature
Charge Current
vs Supply Voltage
Charge Current vs Battery Voltage
1000
800
600
400
200
0
1000
800
600
400
200
0
900
800
700
600
500
400
300
ONSET OF
THERMAL REGULATION
ONSET OF
THERMAL REGULATION
R
= 1.25k
IDC
R
= R
= 2k
IDC
IUSB
= 5V
25
R
V
JA
= 1.25k
= 4V
V
V
θ
= V
USBIN
V
JA
R
= V
= 5V
USBIN
IDC
BAT
= 35°C/W
DCIN
BAT
JA
DCIN
= 4V
θ
= 40°C/W
θ
= 40°C/W
= 1.25k
IDC
4.0
6.0
7.0 7.5
4.5 5.0 5.5
6.5
(V)
8.0
50
100 125
2.4
3.0 3.3 3.6
(V)
3.9
4.5
–50 –25
0
75
4.2
2.7
V
V
DCIN
TEMPERATURE (°C)
BAT
3550-1 G11
3550-1 G10
3550-1 G12
DCIN Power FET On-Resistance
vs Temperature
USBIN Power On-Resistance
vs Temperature
ENABLE Pin Threshold Voltage
(On-to-Off) vs Temperature
550
500
450
400
350
300
250
900
850
800
750
700
650
600
800
750
700
650
600
550
500
450
400
350
V
I
= 4V
= 200mA
V
I
= 4V
= 200mA
BAT
BAT
BAT
BAT
V
= V
= 5V
USBIN
DCIN
50
TEMPERATURE (°C)
100 125
–50 –25
0
25
75
50
TEMPERATURE (°C)
100 125
–50
25
50
75
100
–50 –25
0
25
75
–25
0
TEMPERATURE (°C)
3550-1 G13
3550-1 G14
3550-1 G15
DCIN Shutdown Current
vs Temperature
USBIN Shutdown Current
vs Temperature
ENABLE Pin Pulldown Resistance
vs Temperature
50
45
40
35
30
25
20
15
10
5
2.8
2.6
2.4
2.2
2.0
1.8
1.6
45
40
35
30
25
20
15
10
5
V
V
= 8V
= 5V
DCIN
DCIN
V
V
= 8V
= 5V
USBIN
USBIN
V
= 4.3V
DCIN
V
= 4.3V
USBIN
ENABLE = 5V
50 100
TEMPERATURE (°C)
ENABLE = 0V
50 100
TEMPERATURE (°C)
0
0
–50 –25
0
25
75
–50 –25
0
25
75
–50 –25
0
25
50
TEMPERATURE (°C)
75
100
3550-1 G16
3550-1 G17
3550-1 G18
35501f
6
LTC3550-1
U W
TYPICAL PERFOR A CE CHARACTERISTICS
T = 25°C, unless otherwise noted.
A
Undervoltage Lockout Threshold
vs Temperature
Recharge Threshold Voltage
vs Temperature
Battery Drain Current
vs Temperature
5
4
4.25
4.20
4.15
4.10
4.05
4.00
3.95
3.90
3.85
4.16
4.14
4.12
4.10
4.08
4.06
4.04
V
V
= 4.2V
DCIN USBIN
BAT
, V
(NOT CONNECTED)
DCIN UVLO
3
V
= V
= 4.3V
USBIN
DCIN
2
V
= V
= 8V
USBIN
DCIN
1
USBIN UVLO
0
–1
75
–50
–25
0
25
50
100
–50
0
25
50
75
100
–25
75
–50
–25
0
25
50
100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
3550-1 G19
3550-1 G21
3550-1 G20
Charge Current During Turn-On
and Turn-Off
Buck Regulator Efficiency
vs Output Current
Buck Regulator Efficiency vs V
CC
100
95
100
90
80
70
60
50
V
= 2.7V
CC
I
= 100mA
= 10mA
I
OUT
BAT
500mA/DIV
90
85
V
= 4.2V
CC
I
OUT
V
= 3.6V
CC
ENABLE
5V/DIV
80
75
70
I
= 600mA
3
OUT
2
4
5
6
V
DCIN
= 5V
100µs/DIV
0.1
1
10
(mA)
100
1000
R
= 1.25k
V
(V)
IDC
I
LOAD
CC
35501 G24
3550-1 G22
35501 G23
Buck Regulator Output Voltage
vs Temperature
Oscillator Frequency
vs Temperature
Oscillator Frequency vs V
CC
1.91
1.90
1.89
1.88
1.87
1.86
1.85
1.84
1.70
1.65
1.60
1.55
1.50
1.45
1.40
1.35
1.30
1.8
1.7
1.6
1.5
1.4
1.3
1.2
V
OUT
= 3.6V
= 100mA
CC
V
= 3.6V
CC
I
50
TEMPERATURE (°C)
100 125
50
TEMPERATURE (°C)
100 125
–50 –25
0
25
75
–50 –25
0
25
75
2
3
4
5
6
V
(V)
CC
3550-1 G27
3550-1 G25
3550-1 G26
35501f
7
LTC3550-1
U W
TYPICAL PERFOR A CE CHARACTERISTICS
T = 25°C, unless otherwise noted.
A
Buck Regulator Output Voltage
Buck Regulator Switches R
DS(ON)
vs Load Current
R
vs V
vs Temperature
DS(ON)
CC
0.7
0.6
1.90
1.89
1.88
1.87
1.86
1.85
0.7
0.6
T
= 25°C
V
= 3.6V
A
CC
V
= 2.7V
CC
V
= 3.6V
CC
V
= 4.2V
CC
0.5
0.4
0.3
0.2
0.1
0.5
0.4
0.3
0.2
0.1
MAIN
SWITCH
SYNCHRONOUS
SWITCH
MAIN SWITCH
SYNCHRONOUS SWITCH
0
0
5
7
0
1
2
3
V
4
6
50
TEMPERATURE (°C)
100 125
–50 –25
0
25
75
0
700
900
800
100 200 300 400 500 600
(mA)
(V)
I
CC
LOAD
35501 G28
3550-1 G29
3550-1 G30
Buck Regulator Supply
Current vs V
Buck Regulator Supply Current
vs Temperature
Switch Leakage Current
vs Temperature
CC
50
50
45
40
35
30
25
20
15
10
5
300
250
200
150
V
V
I
= 3.6V
V
I
= 1.875V
= 0A
CC
V
= 5.5V
CC
OUT
LOAD
45
40
35
30
25
20
15
10
5
= 1.875V
OUT
RUN = 0V
= 0A
LOAD
100
50
0
MAIN SWITCH
SYNCHRONOUS SWITCH
0
0
2
3
4
5
6
–50
0
25
50
75 100 125
–50
25
50
75
100 125
–25
–25
0
V
(V)
TEMPERATURE (°C)
TEMPERATURE (°C)
CC
3550-1 G31
3550-1 G32
3550-1 G33
Switch Leakage Current vs V
Burst Mode Operation
CC
120
100
80
60
40
20
0
RUN = 0V
SW
5V/DIV
SYNCHRONOUS
SWITCH
V
OUT
20mV/DIV
MAIN
SWITCH
I
L
200mA/DIV
35501 G35
V
CC
= 3.6V
= 10mA
4µs/DIV
I
LOAD
0
2
3
4
5
6
1
V
(V)
CC
3550-1 G34
35501f
8
LTC3550-1
U W
TYPICAL PERFOR A CE CHARACTERISTICS
T = 25°C, unless otherwise noted.
A
Start-Up from Shutdown
Load Step
Load Step
V
OUT
V
OUT
RUN
2V/DIV
100mV/DIV
100mV/DIV
AC COUPLED
AC COUPLED
V
OUT
1V/DIV
I
L
I
I
L
L
500mA/DIV
500mA/DIV
500mA/DIV
35501 G38
35501 G37
35501 G36
V
I
= 3.6V
LOAD
20µs/DIV
V
I
= 3.6V
LOAD
20µs/DIV
CC
V
I
= 3.6V
LOAD
40µs/DIV
CC
CC
= 50mA TO 600mA
= 0mA TO 600mA
= 600mA
Load Step
Load Step
V
V
OUT
100mV/DIV
AC COUPLED
OUT
100mV/DIV
AC COUPLED
I
L
I
L
500mA/DIV
500mA/DIV
35501 G39
35501 G40
V
LOAD
= 3.6V
20µs/DIV
V
LOAD
= 3.6V
20µs/DIV
CC
CC
I
= 100mA TO 600mA
I
= 200mA TO 600mA
35501f
9
LTC3550-1
U
U
U
PI FU CTIO S
V
(Pin 7): Buck Regulator Input Supply Pin. Must be
USBIN (Pin 1): USB Input Supply Pin. Provides power to
thebatterycharger.Themaximumsupplycurrentis650mA.
This should be bypassed with a 1µF capacitor.
CC
closely decoupled to GND (Pins 8, 9) with a 2.2µF or
greater ceramic capacitor.
GND (Pins 8, 9): Ground.
IUSB (Pin 2): USB Charge Current Program and Monitor
Pin. The charge current can be set by connecting a resis-
SW (Pin 10): Switch Node Connection to Inductor. This
pin connects to the drains of the internal main (top) and
synchronous (bottom) power MOSFET switches.
tor, R , to ground. When charging in constant-current
IUSB
mode, this pin servos to 1V. The voltage on this pin can
be used to measure the charge current delivered from the
USB input using the following formula:
RUN (Pin 11): Buck Regulator Run Control Input. Forcing
this pin above 1.5V enables the regulator. Forcing this pin
below 0.3V shuts it down. In shutdown, all buck regulator
functions are disabled drawing <1µA supply current from
V
IUSB
IBAT
=
• 1000
RIUSB
V . Do not leave RUN floating.
CC
ITERM (Pin 3): Termination Current Threshold Program
ENABLE (Pin 12): Charger Enable Input. When the
LTC3550-1 is charging from the DCIN source, a logic low
on this pin enables the charger. When the LTC3550-1 is
charging from the USBIN source, a logic high on this pin
enables the charger. If this input is left floating, an internal
2MΩ pulldown resistor defaults the LTC3550-1 to charge
when a wall adapter is applied and to shut down if only
the USB source is applied.
Pin. The current termination threshold, I
, can be
TERMINATE
TERMINATE
,toground.I
setbyconnectingaresistor,R
ITERM
is set by the following formula:
100V
RITERM
ITERMINATE
=
When the charge current, I , falls below the termination
BAT
threshold, charging stops and the CHRG output becomes
high impedance.
USBPWR(Pin13):Open-DrainUSBPowerStatusOutput.
When the voltage on the USBIN pin is sufficient to begin
charging and there is insufficient power at DCIN, the
USBPWRpinishighimpedance. Inallothercases, thispin
is pulled low by an internal N-channel MOSFET, provided
that there is power present at DCIN, USBIN, or BAT inputs.
This output is capable of sinking up to 1mA, making it
suitable for driving high impedance logic inputs.
This pin is internally clamped to approximately 1.5V. Driv-
ing this pin to voltages beyond the clamp voltage should
be avoided.
PWR (Pin 4): Open-Drain Power Supply Status Output.
When the DCIN or USBIN pin voltage is sufficient to
begin charging (i.e., when the supply is greater than
the undervoltage lockout threshold and at least 180mV
above the battery terminal), the PWR pin is pulled low by
an internal N-channel MOSFET. Otherwise, PWR is high
impedance. The output is capable of sinking up to 10mA,
making it suitable for driving an LED.
IDC (Pin 14): Wall Adapter Charge Current Program and
Monitor Pin. The charge current is set by connecting a
resistor, R , to ground. When charging in constant-
IDC
current mode, this pin servos to 1V. The voltage on this
pin can be used to measure the charge current using the
following formula:
CHRG (Pin 5): Open-Drain Charge Status Output. When
the LTC3550-1 is charging, the CHRG pin is pulled low by
an internal N-channel MOSFET. When the charge cycle is
completed, CHRG becomes high impedance. This output
is capable of sinking up to 10mA, making it suitable for
driving an LED.
V
RIDC
IDC
IBAT
=
• 1000
BAT (Pin 15): Charger Output. This pin provides charge
current to the battery and regulates the final float voltage
to 4.2V.
V
(Pin 6): Output Voltage Feedback Pin. Receives the
OUT
feedback voltage from the buck regulator output.
35501f
10
LTC3550-1
U
U
U
PI FU CTIO S
DCIN (Pin 16): Wall Adapter Input Supply Pin. Provides
power to the battery charger. The maximum supply
current is 950mA. This should be bypassed with a 1µF
capacitor.
Exposed Pad (Pin 17): GND. The exposed backside of the
packageisgroundandmustbesolderedtothePCBground
for electrical connection and maximum heat transfer.
W
BLOCK DIAGRA
DCIN
16
BAT
15
USBIN
1
CC/CV
REGULATOR
CC/CV
REGULATOR
FREQ
SHIFT
V
6
OSC
OUT
SLOPE
COMP
R1
R2
1mA MAX
10mA MAX
10mA MAX
+
–
+
–
13
4
USBPWR
PWR
+
–
0.6V
I
TH
DC
SOFT-
START
USB
EA
4.15V
3.95V
BAT
SOFT-
START
BURST
CLAMP
DCIN UVLO
USBIN UVLO
+
–
+
–
V
7
CC
BAT
CHRG
5
5Ω
+
–
I
COMP
4.1V
+
Q
Q
S
R
RECHRG
RECHARGE
BAT
–
RS LATCH
ANTI-
SHOOT-
THRU
LOGIC
SW
10
SWITCHING
LOGIC
DC_ENABLE
USB_ENABLE
T
+
DIE
TERM
AND
THERMAL
REGULATION
CHARGER CONTROL
BLANKING
CIRCUIT
+
–
105°C
–
I
RCMP
12
ENABLE
R
ENABLE
100mV
+
I
I
I
BAT
BAT
BAT
/1000
/1000
/1000
TERMINATION
–
3
14
2
11
RUN
8, 9, 17
GND
ITERM
IDC
IUSB
R
ITERM
R
IDC
R
IUSB
35501f
11
LTC3550-1
U
OPERATIO
input (USBIN) is supplying power; logic low disables the
charger and logic high enables it (the default is the
shutdown state). The DCIN input draws 20µA when the
charger is in shutdown. The USBIN input draws 18µA dur-
ing shutdown if no power is applied to DCIN, but draws
The LTC3550-1 consists of two main blocks: a lithium-ion
battery charger and a high-efficiency buck converter that
can be powered from the battery. The charger is designed
to efficiently manage charging of a single-cell lithium-ion
battery from two separate power sources: a wall adapter
and USB power bus. The internal P-channel MOSFETs
can supply up to 950mA from the wall adapter source
and 500mA from the USB power source. The final float
voltage accuracy is 0.6ꢀ.
only 10µA when V
> V
.
DCIN
USBIN
Once the charger is enabled, it enters constant-current
mode, where the programmed charge current is supplied
to the battery. When the BAT pin approaches the final
float voltage (4.2V), the charger enters constant-voltage
mode and the charge current begins to decrease. Once
the charge current drops below the programmed termina-
The buck converter uses a constant frequency, current
mode step-down architecture. Both the main (P-channel
MOSFET)andsynchronous(N-channelMOSFET)switches
forthebuckconverterareinternal.TheLTC3550-1requires
no external diodes or sense resistors.
tion threshold (set by the external resistor R
), the
ITERM
internal P-channel MOSFET is shut off and the charger
enters standby mode.
Lithium-Ion Battery Charger
In standby mode, the charger sits idle and monitors the
battery voltage using a comparator with a 6ms filter time
A charge cycle begins when the voltage at either the DCIN
pin or USBIN pin rises above the UVLO threshold level and
the charger is enabled through the ENABLE pin. The “on”
state of this pin depends on which source is supplying
power. When the wall adapter input (DCIN) is supply-
ing power, logic low enables the charger and logic high
disables it (a 2MΩ pulldown defaults the charger to
the charging state). The opposite is true when the USB
(t ). A charge cycle automatically restarts when the
RECHRG
batteryvoltagefallsbelow4.1V(whichcorrespondstoap-
proximately 80ꢀ to 90ꢀ battery capacity). This ensures
that the battery is kept near a fully charged condition and
eliminates the need for periodic charge cycle initiations.
Figure 1 uses a state diagram to describe the behavior of
the LTC3550-1 battery charger.
STARTUP
DCIN POWER APPLIED
ONLY USB POWER APPLIED
POWER SELECTION
USBIN POWER
REMOVED OR
DCIN POWER
APPLIED
DCIN POWER
REMOVED
CHARGE
MODE
CHARGE
MODE
FULL CURRENT
FULL CURRENT
CHRG STATE: PULLDOWN
CHRG STATE: PULLDOWN
I
< I
BAT TERMINATE
I
< I
BAT TERMINATE
IN VOLTAGE MODE
IN VOLTAGE MODE
STANDBY
MODE
STANDBY
MODE
NO CHARGE CURRENT
CHRG STATE: Hi-Z
NO CHARGE CURRENT
CHRG STATE: Hi-Z
BAT < 4.1V
BAT < 4.1V
ENABLE
DRIVEN HIGH
ENABLE
DRIVEN LOW
SHUTDOWN
MODE
SHUTDOWN
MODE
ENABLE
DRIVEN LOW
ENABLE
DRIVEN HIGH
I
DROPS TO 20µA
I
DROPS TO 18µA
DCIN
USBIN
DCIN POWER
REMOVED
USBIN POWER
REMOVED OR DCIN
POWER APPLIED
CHRG STATE: Hi-Z
CHRG STATE: Hi-Z
3550-1 F01
Figure 1. LTC3550-1 State Diagram of a Charge Cycle
35501f
12
LTC3550-1
U
OPERATIO
600mA Step-Down Regulator
then be determined by the input voltage minus the voltage
drop across the P-channel MOSFET and the inductor.
The LTC3550-1 regulator uses a constant frequency, cur-
rentmodestep-downarchitecture.Boththetop(P-channel
MOSFET) and bottom (N-channel MOSFET) switches are
internal. During normal operation, the internal top power
MOSFET is turned on each cycle when the oscillator sets
the RS latch, and is turned off when the current com-
Animportantdetailtorememberisthatatlowinputsupply
voltages, the R
of the P-channel switch increases
DS(ON)
(see Typical Performance Characteristics). Therefore,
the user should calculate the power dissipation when the
LTC3550-1 is used at 100ꢀ duty cycle with low input
voltage (See Thermal Considerations in the Applications
Information section).
parator, I
, resets the RS latch. The peak inductor
COMP
current at which I
resets the RS latch, is controlled
COMP
by the output of error amplifier EA. When the load current
increases, it causes a slight decrease in the output voltage
Battery Charger Power Source Selection
(V ), relative to the internal reference, which in turn
OUT
The LTC3550-1 can charge a battery from either the wall
adapterinputortheUSBportinput. Thechargerautomati-
cally senses the presence of voltage at each input. If both
powersourcesarepresent, thechargerdefaultstothewall
adapter source provided sufficient power is present at the
DCIN input. “Sufficient power” is defined as:
causes the EA amplifier’s output voltage to increase until
the average inductor current matches the new load cur-
rent. While the top MOSFET is off, the bottom MOSFET is
turnedonuntileithertheinductorcurrentstartstoreverse,
as indicated by the current reversal comparator I
the beginning of the next clock cycle.
, or
RCMP
• Supply voltage is greater than the UVLO threshold.
Burst Mode® Operation
• Supply voltage is greater than the battery voltage by
50mV (180mV rising, 50mV falling).
The LTC3550-1 buck regulator is capable of Burst Mode
operation in which the internal power MOSFETs operate
intermittently based on load current demand.
Theopendrainpowerstatusoutputs(PWRandUSBPWR)
indicate which power source has been selected. Table 1
describes the behavior of these status outputs.
InBurstModeoperation,thepeakcurrentoftheinductoris
settoapproximately200mAregardlessoftheoutputload.
Each burst event can last from a few cycles at light loads
to almost continuously cycling with short sleep intervals
at moderate loads. In between these burst events, the
power MOSFETs and any unneeded circuitry are turned
off, reducing the quiescent current to 20µA. In this sleep
state, the load current is being supplied solely from the
output capacitor. As the output voltage droops, the EA
amplifier’soutputrisesabovethesleepthresholdsignaling
the BURST comparator to trip and turn the top MOSFET
on. This process repeats at a rate that is dependent on
the load demand.
Table 1. Power Source Selection
V
V
> 3.95V and
> BAT + 50mV
V
V
< 3.95V or
USBIN
USBIN
USBIN
USBIN
< BAT + 50mV
V
V
> 4.15V and
> BAT + 50mV
Device Powered from
Wall Adapter Source;
USBIN Current < 25µA
PWR: LOW
Device Powered from
Wall Adapter Source
DCIN
DCIN
PWR: LOW
USBPWR: LOW
USBPWR: LOW
V
V
< 4.15V or
< BAT + 50mV
Device Powered from
USB Source;
No Charging
DCIN
DCIN
PWR: LOW
PWR: Hi-Z
USBPWR: LOW
USBPWR: Hi-Z
Status Indicators
Dropout Operation
The charge status output (CHRG) has two states: pull-
down and high impedance. The pull-down state indicates
that the LTC3550-1 is in a charge cycle. Once the charge
cycle has terminated or the LTC3550-1 is disabled, the
pin state becomes high impedance. The pull-down state
is strong enough to drive an LED and is capable of sink-
Astheinputsupplyvoltagedecreasestoavalueapproach-
ing the output voltage, the duty cycle increases toward the
maximumon-time.Furtherreductionofthesupplyvoltage
forcesthemainswitchtoremainonformorethanonecycle
until it reaches 100ꢀ duty cycle. The output voltage will
Burst Mode is a registered trademark of Linear Technology Corporation.
ing up to 10mA.
35501f
13
LTC3550-1
U
OPERATIO
Thepowersupplystatusoutput(PWR)hastwostates:pull-
down and high impedance. The pull-down state indicates
that power is present at either DCIN or USBIN. If no power
is applied at either pin, the PWR pin is high impedance,
indicating that the LTC3550-1 lacks sufficient power to
charge the battery. The pull-down state is strong enough
to drive an LED and is capable of sinking up to 10mA.
assurance that the charger will automatically reduce the
current in worst case conditions. DFN package power
considerations are discussed further in the Applications
Information section.
Charge Current Soft-Start and Soft-Stop
Thebatterychargerincludesasoft-startcircuittominimize
the inrush current at the start of a charge cycle. When a
charge cycle is initiated, the charge current ramps from
zero to full-scale current over a period of 250µs. Like-
wise, internal circuitry slowly ramps the charge current
from full-scale to zero in approximately 30µs when the
charger shuts down or self terminates. This minimizes
the transient current load on the power supply during
start-up and shut-off.
The USB power status output (USBPWR) has two states:
pull-down and high impedance. The high impedance state
indicates that the LTC3550-1 is being powered from the
USBINinput.Thepull-downstateindicatesthatthecharger
is either powered from DCIN or is in a UVLO condition
(see Table 1). The pull-down state is capable of sinking
up to 1mA.
Thermal Limiting
Short-Circuit Protection
Aninternalthermalfeedbackloopreducestheprogrammed
charge current if the die temperature attempts to rise
above a preset value of approximately 105°C. This feature
protects the LTC3550-1 from excessive temperature and
allows the user to push the limits of the power handling
capability of a given circuit board without risk of damag-
ing the device. The charge current can be set according
to typical (not worst-case) ambient temperature with the
Whentheregulatoroutput(V )isshortedtoground,the
OUT
frequencyoftheoscillatorisreducedtoabout210kHz,one
seventh the nominal frequency. This frequency foldback
ensures that the inductor current has more time to decay,
thereby preventing runaway. The oscillator’s frequency
will progressively increase to 1.5MHz when V
above 0V.
rises
OUT
35501f
14
LTC3550-1
U
W U U
APPLICATIO S I FOR ATIO
Figure 2 shows the basic LTC3550-1 application circuit.
External component selection is driven by the charging
requirements and the buck regulator load requirements.
Programming Charge Termination
The charge cycle terminates when the charge current falls
belowtheprogrammedterminationthresholdduringcon-
stant-voltagemode.Thisthresholdissetbyconnectingan
LTC3550-1
RUN SW
L1
V
OUT
external resistor, R , from the ITERM pin to ground.
ITERM
1.875V
600mA
WALL
The charge termination current threshold (I
set by the following equation:
) is
C
TERMINATE
OUT
ADAPTER
DCIN
USBIN
IUSB
IDC
V
OUT
V
USB
POWER
CC
C2
BAT
100V
ITERMINATE
100V
RITERM
R
C
RITERM
=
,ITERMINATE =
IUSB
IN
ITERM
4.2V
SINGLE
CELL Li-Ion
BATTERY
+
GND
C1
R
ITERM
R
IDC
The termination condition is detected by using an internal
filtered comparator to monitor the ITERM pin. When the
ITERM pin voltage drops below 100mV* for longer than
3550-1 F02
Figure 2. LTC3550-1 Basic Circuit
t
(typically 1.5ms), charging is terminated. The
TERMINATE
Programming and Monitoring Charge Current
charge current is latched off and the LTC3550-1 enters
standby mode.
The charge current delivered to the battery from the wall
adapter supply is programmed using a single resistor
from the IDC pin to ground. Likewise, the charge current
from the USB supply is programmed using a single resis-
tor from the IUSB pin to ground. The program resistor
When charging, transient loads on the BAT pin can cause
the ITERM pin to fall below 100mV for short periods of
time before the DC charge current has dropped below the
programmed termination current. The 1.5ms filter time
and the charge current (I ) are calculated using the
CHRG
following equations:
(t
) on the termination comparator ensures that
TERMINATE
transient loads of this nature do not result in premature
chargecycletermination.Oncetheaveragechargecurrent
drops below the programmed termination threshold, the
LTC3550-1terminatesthechargecycleandstopsproviding
any current out of the BAT pin. In this state, any load on
the BAT pin must be supplied by the battery.
1000V
ICHRG(DC)
1000V
1000V
RIDC
=
,ICHRG(DC) =
RIDC
1000V
RIUSB
=
, ICHRG(USB) =
ICHRG(USB)
RIUSB
Buck Regulator Inductor Selection
Charge current out of the BAT pin can be determined at
any time by monitoring the IDC or IUSB pin voltage and
using the following equations:
For most applications, the value of the inductor will fall in
the range of 1µH to 4.7µH. Its value is chosen based on
the desired inductor ripple current. Large value inductors
lower ripple current and small value inductors result in
V
IDC
RIDC
IBAT
IBAT
=
=
• 1000 (charging from wall adapter)
higher ripple currents. Higher V or V
also increases
CC
OUT
V
IUSB
the ripple current as shown in Equation 1. A reasonable
• 1000 (charging fromUSB supply)
RIUSB
starting point for setting ripple current is ΔI = 240mA
L
(40ꢀ of 600mA).
⎛
⎞
⎠
VOUT
fO •L
VOUT
VCC
∆IL =
• 1−
⎜
⎝
⎟
(1)
* Any external sources that hold the ITERM pin above 100mV will prevent the LTC3550-1
from terminating a charge cycle.
35501f
15
LTC3550-1
U
W U U
APPLICATIO S I FOR ATIO
The DC current rating of the inductor should be at least
equal to the maximum load current plus half the ripple
current to prevent core saturation. Thus, a 720mA rated
inductor should be enough for most applications (600mA
+120mA). Forbestefficiency, choosealowDC-resistance
inductor.
C and C
Selection
IN
OUT
Incontinuousmode,thesourcecurrentofthetopMOSFET
is a square wave of duty cycle V /V . To prevent large
voltage transients, a low ESR input capacitor sized for the
maximumRMScurrentmustbeused.ThemaximumRMS
capacitor current is given by:
OUT CC
TheinductorvaluealsohasaneffectonBurstModeopera-
tion. The transition to low current operation begins when
the inductor current peaks fall to approximately 200mA.
VOUT
VCC − VOUT
(
)
CIN required IRMS ≅ IOMAX
VCC
Lower inductor values (higher ΔI ) will cause this to occur
L
(2)
at lower load currents, which can cause a dip in efficiency
in the upper range of low current operation. In Burst Mode
operation, lower inductance values will cause the burst
frequency to increase.
This formula has a maximum at V = 2V , where I
CC
OUT
RMS
= I /2. This simple worst-case condition is commonly
OUT
usedfordesignbecauseevensignificantdeviationsdonot
offer much relief. Note that the capacitor manufacturer’s
ripple current ratings are often based on 2000 hours of
life. This makes it advisable to further derate the capaci-
tor, or choose a capacitor rated at a higher temperature
than required. Always consult the manufacturer if there
is any question.
Inductor Core Selection
Different core materials and shapes will change the
size/current and price/current relationship of an induc-
tor. 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. The choice of which
style inductor to use often depends more on the price vs
sizerequirementsandanyradiatedfield/EMIrequirements
than on what the LTC3550-1 requires to operate. Table 2
shows some typical surface mount inductors that work
well in LTC3550-1 applications.
The selection of C
is driven by the required effective
OUT
series resistance (ESR).
Typically, once the ESR requirement for C
has been
OUT
met, the RMS current rating generally far exceeds the
I
requirement. The output ripple ΔV
is
RIPPLE(P-P)
determined by:
OUT
⎛
⎜
⎝
⎞
⎠
1
∆VOUT ≅ ∆IL ESR +
⎟
Table 2. Representative Surface Mount Inductors
8fCOUT
(3)
= output capacitance
and ΔI = ripple current in the inductor. For a fixed output
voltage, the output ripple voltage is highest at maximum
PART
NUMBER
VALUE
(µH)
DCR
MAX DC
SIZE
(Ω MAX) CURRENT (A) W × L × H (mm)
where f = operating frequency, C
OUT
Sumida
CDRH3D16
1.5
2.2
3.3
4.7
0.043
0.075
0.110
0.162
1.55
1.20
1.10
0.90
3.8 × 3.8 × 1.8
L
input voltage since ΔI increases with input voltage.
L
Sumida
CMD4D06
2.2
3.3
4.7
0.116
0.174
0.216
0.950
0.770
0.750
3.5 × 4.3 × 0.8
Aluminum electrolytic and solid tantalum capacitors are
bothavailableinsurfacemountconfigurations.Inthecase
oftantalum,itiscriticalthatthecapacitorsaresurgetested
for use in switching power supplies. An excellent choice is
the AVX TPS series of surface mount tantalum. These are
specially constructed and tested for low ESR so they give
the lowest ESR for a given volume. Other capacitor types
include Sanyo POSCAP, Kemet T510 and T495 series, and
Sprague 593D and 595D series. Consult the manufacturer
Panasonic
ELT5KT
3.3
4.7
0.17
0.20
1.00
0.95
4.5 × 5.4 × 1.2
2.5 × 3.2 × 2.0
Murata
LQH32CN
1.0
2.2
4.7
0.060
0.097
0.150
1.00
0.79
0.65
for other specific recommendations.
35501f
16
LTC3550-1
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APPLICATIO S I FOR ATIO
Using Ceramic Input and Output Capacitors
than the DC bias current. In continuous mode, I
GATECHG
= f(Q + Q ) where Q and Q are the gate charges of
T
B
T
B
Higher capacitance values, lower cost ceramic capacitors
are now becoming available in smaller case sizes. Their
high ripple current, high voltage rating and low ESR make
themidealforswitchingregulatorapplications.Becausethe
LTC3550-1’s control loop does not depend on the output
capacitor’s ESR for stable operation, ceramic capacitors
can be used freely to achieve very low output ripple and
small circuit size.
the internal top and bottom switches. Both the DC bias
and gate charge losses are proportional to V and
CC
thus their effects will be more pronounced at higher
supply voltages.
2
2. I R losses are calculated from the resistances of the
internal switches, R , and external inductor R . In
SW
L
continuous mode, the average output current flowing
through inductor L is “chopped” between the main
switch and the synchronous switch. Thus, the series
resistance looking into the SW pin is a function of both
When choosing the input and output ceramic capacitors,
choose the X5R or X7R dielectric formulations. These
dielectrics have the best temperature and voltage charac-
teristics of all the ceramics for a given value and size.
top and bottom MOSFET R
(DC) as follows:
and the duty cycle
DS(ON)
R
= (R )(DC) + (R )(1 – DC)
DS(ON)TOP DS(ON)BOT
Efficiency Considerations
SW
The R
for both the top and bottom MOSFETs can
Theefficiencyofaswitchingregulatorisequaltotheoutput
power divided by the input power times 100ꢀ. It is often
useful to analyze individual losses to determine what is
limiting the efficiency and which change would produce
the most improvement. Efficiency can be expressed as:
DS(ON)
be obtained from the Typical Performance Characteristics
2
curves. Thus, to obtain I R losses, simply add R to R
SW
L
and multiply the result by the square of the average output
current. Other losses including C and C
ESR dissipa-
IN
OUT
tive losses and inductor core losses generally account for
less than 2ꢀ total additional loss.
Efficiency = 100ꢀ – (L1 + L2 + L3 + ...)
where L1, L2, etc. are the individual losses as a percent-
age of input power.
1
0.1
Although all dissipative elements in the circuit produce
losses, two main sources usually account for most of
the losses in LTC3550-1 circuits: V quiescent current
0.01
CC
2
and I R losses. The V quiescent current loss dominates
CC
0.001
0.0001
0.00001
the efficiency loss at very low load currents whereas the
2
I R loss dominates the efficiency loss at medium to high
load currents. In a typical efficiency plot, the efficiency
curve at very low load currents can be misleading since
the actual power lost is of no consequence as illustrated
in Figure 3.
0.1
1
10
100
1000
LOAD CURRENT (mA)
3550-1 F03
Figure 3. Power Lost vs Load Current
1. The V quiescent current is due to two components:
CC
the DC bias current as given in the Electrical Charac-
teristics and the internal main switch and synchronous
switch gate charge currents. The gate charge current
results from switching the gate capacitance of the
internal power MOSFET switches. Each time the gate
is switched from high to low to high again, a packet of
charge, dQ, moves from V to ground. The resulting
CC
dQ/dt is the current out of V that is typically larger
CC
35501f
17
LTC3550-1
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APPLICATIO S I FOR ATIO
Thermal Considerations
Most of the charger’s power dissipation is generated from
the internal charger MOSFET. Thus, the power dissipation
is calculated to be:
The battery charger’s thermal regulation feature and the
buckregulator’shighefficiencymakeitunlikelythatenough
power is dissipated to exceed the LTC3550-1 maximum
junction temperature. Nevertheless, it is a good idea to
do some thermal analysis for worst-case conditions.
P
= (V – V ) • I
(5)
D(CHARGER)
IN
BAT
BAT
V is the charger supply voltage (either DCIN or USBIN),
IN
V
BAT
is the battery voltage and I
is the charge cur-
BAT
The junction temperature, T , is given by: T = T + T
J
J
A
RISE
rent.
where T is the ambient temperature. The temperature
A
Example: An LTC3550-1 operating from a 5V wall adapter
(on the DCIN input) is programmed to supply 650mA
full-scale current to a discharged Li-Ion battery with a
voltage of 2.7V.
rise is given by:
T
= P • θ
D JA
RISE
where P is the power dissipated and θ is the thermal
D
JA
resistance from the junction of the die to the ambient
temperature.
The charger power dissipation is calculated to be:
P
= (5V – 2.7V) • 650mA = 1.495W
D(CHARGER)
In most applications the buck regulator does not dissipate
much heat due to its high efficiency. The majority of the
LTC3550-1 power dissipation occurs when charging a
battery. Fortunately, theLTC3550-1automaticallyreduces
the charge current during high power conditions using
a patented thermal regulation circuit. Thus, there is no
needtodesignforworst-casepowerdissipationscenarios
because the LTC3550-1 ensures that the battery charger
power dissipation never raises the junction temperature
above a preset value of 105°C. In the unlikely case that
the junction temperature is forced above 105°C (due to
abnormally high ambient temperatures or excessive buck
regulatorpowerdissipation),thebatterychargecurrentwill
bereducedtozeroandthusdissipatenoheat. Asanadded
measure of protection, even if the junction temperature
reaches approximately 150°C, the buck regulator’s power
switches will be turned off and the SW node will become
high impedance.
For simplicity, assume the buck regulator is disabled and
dissipatesnopower(P
=0).Foraproperlysoldered
D(BUCK)
DHC16 package, the thermal resistance (θ ) is 40°C/W.
JA
Thus, the ambient temperature at which the LTC3550-1
charger will begin to reduce the charge current is:
T = 105°C – 1.495W • 40°C/W
A
T = 105°C – 59.8°C
A
T = 45.2°C
A
The LTC3550-1 can be used above 45.2°C ambient, but
the charge current will be reduced from 650mA. Assum-
ing no power dissipation from the buck converter, the
approximate current at a given ambient temperature can
be approximated by:
105°C – TA
IBAT
=
(V – VBAT) • θJA
(6)
IN
TheconditionsthatcausetheLTC3550-1toreducecharge
currentthroughthermalfeedbackcanbeapproximatedby
considering the power dissipated in the IC. The approxi-
mate ambient temperature at which the thermal feedback
begins to protect the IC is:
Using the previous example with an ambient temperature
of 60°C, the charge current will be reduced to approxi-
mately:
105°C – 60°C
45°C
IBAT
=
=
(5V – 2.7V) • 40°C/W 92°C/A
T = 105°C – T
A
RISE
IBAT = 489mA
T = 105°C – (P • θ )
A
D
JA
Becausetheregulatortypicallydissipatessignificantlyless
heat than the charger (even in worst-case situations), the
calculations here should work well as an approximation.
T = 105°C – (P
A
+ P
) • θ
JA
(4)
D(CHARGER)
D(BUCK)
35501f
18
LTC3550-1
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APPLICATIO S I FOR ATIO
However,theusermaywishtorepeatthepreviousanalysis
totakethebuckregulator’spowerdissipationintoaccount.
Equation (6) can be modified to take into account the
temperature rise due to the buck regulator:
for overshoot or ringing that would indicate a stability
problem. For a detailed explanation of switching control
loop theory, see Application Note 76.
A second, more severe transient is caused by switching
in loads with large (>1µF) supply bypass capacitors. The
discharged bypass capacitors are effectively put in paral-
105°C – TA − (PD(BUCK) • θJA)
IBAT
=
(V – VBAT) • θJA
(7)
IN
lel with C , causing a rapid drop in V . No regulator
OUT
OUT
For optimum performance, it is critical that the exposed
metal pad on the backside of the LTC3550-1 package is
properly soldered to the PC board ground. When correctly
can deliver enough current to prevent this problem if the
load switch resistance is low and it is driven quickly. The
only solution is to limit the rise time of the switch drive
so that the load rise time is limited to approximately (25
2
soldered to a 2500mm double sided 1oz copper board,
the LTC3550-1 has a thermal resistance of approximately
40°C/W. Failure to make thermal contact between the ex-
posed pad on the backside of the package and the copper
board will result in thermal resistances far greater than
40°C/W. As an example, a correctly soldered LTC3550-1
can deliver over 800mA to a battery from a 5V supply
at room temperature. Without a good backside thermal
connection, this number would drop to much less than
500mA.
• C ). Thus, a 10µF capacitor charging to 3.3V would
LOAD
require a 250µs rise time, limiting the charging current
to about 130mA.
Protecting the USB Pin and Wall Adapter Input from
Overvoltage Transients
Caution must be exercised when using ceramic capaci-
tors to bypass the USBIN pin or the wall adapter inputs.
High voltage transients can be generated when the USB
or wall adapter is hot-plugged. When power is supplied
via the USB bus or wall adapter, the cable inductance
along with the self resonant and high Q characteristics of
ceramic capacitors can cause substantial ringing which
could exceed the maximum voltage ratings and damage
the LTC3550-1. Refer to Linear Technology Application
Note 88, entitled “Ceramic Input Capacitors Can Cause
Overvoltage Transients” for a detailed discussion of this
problem. The long cable lengths of most wall adapters
and USB cables makes them especially susceptible to this
problem. To bypass the USB and the wall adapter inputs,
add a 1Ω resistor in series with a ceramic capacitor to
lower the effective Q of the network and greatly reduce the
ringing. A tantalum, OS-CON, or electrolytic capacitor can
beusedinplaceoftheceramicandresistor, astheirhigher
ESR reduces the Q, thus reducing the voltage ringing.
Battery Charger Stability Considerations
Theconstant-voltagemodefeedbackloopisstablewithout
any compensation provided a battery is connected to the
charger output. When the charger is in constant-current
mode, the charge current program pin (IDC or IUSB) is in
the feedback loop, not the battery. The constant-current
mode stability is affected by the impedance at the charge
current program pin. With no additional capacitance on
this pin, the charger is stable with program resistor val-
ues as high as 20k (I
= 50mA); however, additional
CHG
capacitanceonthesenodesreducesthemaximumallowed
program resistor value.
Checking Regulator Transient Response
The regulator loop response can be checked by looking
at the load transient response. Switching regulators take
several cycles to respond to a step in load current. When
The oscilloscope photograph in Figure 4 shows how seri-
ous the overvoltage transient can be for the USB and wall
adapterinputs.Forbothtraces,a5Vsupplyishot-plugged
using a three foot long cable. For the top trace, only a
4.7µF ceramic X5R capacitor (without the recommended
1Ω series resistor) is used to locally bypass the input.
This trace shows excessive ringing when the 5V cable
a load step occurs, V
immediately shifts by an amount
OUT
equal to (ΔI
• ESR), where ESR is the effective series
LOAD
resistance of C . ΔI
also begins to charge or dis-
OUT
LOAD
charge C , which generates a feedback error signal. The
OUT
regulator loop then acts to return V
value. During this recovery time V
to its steady state
can be monitored
OUT
OUT
is inserted, with the overvoltage spike reaching 10V. For
35501f
19
LTC3550-1
U
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APPLICATIO S I FOR ATIO
the bottom trace, a 1Ω resistor is added in series with the
4.7µF capacitor to locally bypass the 5V input. This trace
shows the clean response resulting from the addition of
the 1Ω resistor.
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the LTC3550-1. These items are also illustrated graph-
ically in Figures 5 and 6. Check the following in your
layout:
1. The power traces, consisting of the GND trace, the SW
4.7μF ONLY
2V/DIV
trace and the V trace should be kept short, direct
CC
and wide.
2. Does the V
pin connect directly to the output?
OUT
3. Does the (+) plate of C connect to V as closely as
4.7μF + 1Ω
IN
CC
2V/DIV
possible? This capacitor provides the AC current to the
internal power MOSFETs.
3550-1 F04
20μs/DIV
4. Keep the (–) plates of C and C
as close as
OUT
IN
Figure 4. Waveforms Resulting from
Hot-Plugging a 5V Input Supply When
Using Ceramic Bypass Capacitors
possible.
5. Solder the exposed pad on the backside of the package
to PC board ground for optimum thermal performance.
The thermal resistance of the package can be further
enhanced by increasing the area of the copper used for
PC board ground.
Evenwiththeadditional1Ωresistor,baddesigntechniques
and poor board layout can often make the overvoltage
problem even worse. System designers often add extra
inductance in series with input lines in an attempt to mini-
mize the noise fed back to those inputs by the application.
In reality, adding these extra inductances only makes the
overvoltage transients worse. Since cable inductance is
one of the fundamental causes of the excessive ringing,
adding a series ferrite bead or inductor increases the ef-
fective cable inductance, making the problem even worse.
For this reason, do not add additional inductance (ferrite
beads or inductors) in series with the USB or wall adapter
inputs.Forthemostrobustsolution,6Vtransorbsorzener
diodes may also be added to further protect the USB and
wall adapter inputs. Two possible protection devices are
the SM2T from STMicroelectronics and the EDZ series
devices from ROHM.
Design Example
As a design example, assume the LTC3550-1 is used
in a single lithium-ion battery-powered cellular phone
application. The battery is charged by either plugging
a wall adapter into the phone or putting the phone in a
USB cradle. The optimum charge current for this parti-
cular lithium-ion battery is determined to be 800mA.
Starting with the charger, choosing R
programs the charger for 806mA. Choosing R
be 2.1k programs the charger for 475mA when charging
from the USB cradle, ensuring that the charger never
exceeds the 500mA maximum current supplied by the
to be 1.24k
IDC
to
IUSB
USB port. A good rule of thumb for I
is one-
is picked to be
TERMINATE
Always use an oscilloscope to check the voltage wave-
forms at the USBIN and DCIN pins during USB and wall
adapter hot-plug events to ensure that overvoltage
transients have been adequately removed.
tenth the full charge current, so R
ITERM
1.24k (I
= 80mA).
TERMINATE
Moving on to the step-down converter, V will be pow-
CC
ered from the battery which can range from a maximum
of 4.2V down to about 2.7V. The load current requirement
is a maximum of 600mA but most of the time it will be in
standby mode, requiring only 2mA. Efficiency at both low
35501f
20
LTC3550-1
U
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APPLICATIO S I FOR ATIO
and high load currents is important. With this information
we can calculate L using Equation (1),
A 2.2µH inductor works well for this application. For best
efficiency choose a 720mA or greater inductor with less
than 0.2Ω series resistance. C will require an RMS cur-
IN
⎛
⎞
⎠
VOUT
fO •L
VOUT
VCC
rent rating of at least 0.3A = I
/2 at temperature
∆IL =
• 1−
LOAD(MAX)
⎜
⎝
⎟
and C
will require an ESR of less than 0.25Ω. In most
cases, a ceramic capacitor will satisfy this requirement.
OUT
Substituting V
O
= 1.875V, V = 4.2V, ΔI = 240mA and
CC L
OUT
Figure 7 shows the complete circuit along with its ef-
ficiency curve.
f = 1.5MHz in Equation (3) gives:
1.875V
1.5MHz •(240mA)
1.875V
4.2V
⎛
⎞
⎠
L =
• 1−
= 2.88µH
⎜
⎝
⎟
LTC3550-1
BOLD LINES INDICATE
HIGH CURRENT PATHS
6
V
V
OUT
7
8
10
9
V
CC
SW
CC
+
–
C
IN
L1
GND
GND
–
+
V
OUT
17
C
OUT
3550-1 F05
Figure 5. DC-DC Converter Layout Diagram
VIA TO V
VIA TO V
CC
OUT
SW
C
IN
L1
V
CC
GND
C
OUT
V
OUT
3550-1 F06
Figure 6. DC-DC Converter Suggested Layout
35501f
21
LTC3550-1
U
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APPLICATIO S I FOR ATIO
V
OUT
LTC3550-1
RUN SW
2.2µH*
1.875V
600mA
WALL
10µF**
ADAPTER
DCIN
USBIN
IUSB
IDC
V
OUT
CER
800mA (WALL)
V
USB
POWER
CC
475mA (USB)
1µF
BAT
4.7µF†
2.1k
1%
ITERM
4.2V
+
GND
1µF
SINGLE-
CELL Li-Ion
BATTERY
1.24k
1%
1.24k
1%
3550-1 F07a
*
MURATA LQH32CN2R2M33
** TAIYO YUDEN JMK316BJ106ML
†
TAIYO YUDEN LMK212BJ475MG
Figure 7a. Design Example Circuit
100
90
80
70
60
50
V
= 2.7V
CC
V
= 4.2V
CC
V
= 3.6V
CC
0.1
1
10
(mA)
100
1000
I
LOAD
35501 F07b
Figure 7b. Buck Regulator Efficiency vs Output Current
U
TYPICAL APPLICATIO S
Full Featured Dual Input Charger Plus Step-Down Converter
800mA (WALL)
475mA (USB)
LTC3550-1
BAT
WALL
ADAPTER
DCIN
4.7µF
1k
+
USB
POWER
USBIN
4.2V
SINGLE-CELL
Li-Ion BATTERY
PWR
1µF
1µF
1k
CHRG
V
CC
IUSB
IDC
2.2µH
V
OUT
SW
OUT
1.875V
600mA
2.1k
1%
1.24k
1%
10µF
CER
V
ITERM
GND
1k
1%
3550-1 TA03
35501f
22
LTC3550-1
U
PACKAGE DESCRIPTIO
DHC Package
16-Lead Plastic DFN (5mm × 3mm)
(Reference LTC DWG # 05-08-1706)
0.65 0.05
3.50 0.05
1.65 0.05
2.20 0.05 (2 SIDES)
PACKAGE
OUTLINE
0.25 0.05
0.50 BSC
4.40 0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
R = 0.115
TYP
0.40 0.10
16
5.00 0.10
(2 SIDES)
9
R = 0.20
TYP
3.00 0.10 1.65 0.10
(2 SIDES)
(2 SIDES)
PIN 1
TOP MARK
(SEE NOTE 6)
PIN 1
NOTCH
(DHC16) DFN 1103
8
1
0.25 0.05
0.75 0.05
0.200 REF
0.50 BSC
4.40 0.10
(2 SIDES)
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING PROPOSED TO BE MADE VARIATION OF VERSION (WJED-1) IN JEDEC
PACKAGE OUTLINE MO-229
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
35501f
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.
23
LTC3550-1
U
TYPICAL APPLICATIO S
™
Dual Input Charger Plus Step-Down Converter with Wall Adapter PowerPath
LTC3550-1
DCIN
WALL ADAPTER
1µF
USBIN
IUSB
V
CC
USB
POWER
1k
4.7µF
1µF
800mA (WALL)
475mA (USB)
BAT
SW
2.2µH
V
OUT
1.875V
600mA
IDC
+
2.1k
1%
4.2V
10µF
CER
V
ITERM
OUT
1.24k
1%
SINGLE-CELL
GND
1k
1%
Li-Ion BATTERY
3550-1 TA04
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
V : 2.5V to 5.5V, V
LTC3406/LTC3406B 1.5MHz, 600mA Synchronous
) = 0.6V, I = 20µA, ThinSOT Package
OUT(MIN Q
IN
Step-Down DC/DC Converter in ThinSOTTM
LTC3455
LTC3456
LTC4054
Dual DC/DC Converter with USB Power
Management and Li-Ion Battery Charger
Efficiency >96ꢀ, Accurate USB Current Limiting (500mA/100mA), 4mm × 4mm
QFN-24 Package
2-Cell Multi-Output DC/DC Converter
with USB Power Manager
Seamless Transition Between 2-Cell Battery, USB and AC Wall Adapter Input Power
Sources, QFN Package
Standalone Linear Li-Ion Battery Charger Thermal Regulation Prevents Overheating, C/10 Termination, Up to 800mA
with Integrated Pass Transistor in
ThinSOT
Charge Current
LTC4055
LTC4058
USB Power Controller and Battery Charger Charges Single-Cell Li-Ion Batteries Directly from USB Port, Thermal Regulation,
4mm × 4mm QFN-16 Package
Standalone 950mA Lithium-Ion Charger
in DFN
C/10 Charge Termination, Battery Kelvin Sensing, 7ꢀ Charge Accuracy
LTC4063
LTC4068
Standalone Li-Ion Charger Plus LDO
4.2V, 0.35ꢀ Float Voltage, Up to 1A Charge Current, 100mA LDO
Standalone Linear Li-Ion Battery Charger Charge Current up to 950mA, Thermal Regulation, 3mm × 3mm DFN-8 Package
with Programmable Termination
LTC4075
LTC4076
LTC4077
Dual Input Standalone Li-Ion Battery
Charger
Charges Single-Cell Li-Ion Batteries from Wall Adapter and USB Inputs with Automatic
Input Power Detection and Selection, 950mA Charger Current, Thermal Regulation,
C/X Charge Termination, 3mm × 3mm DFN Package
Dual Input Standalone Li-Ion Battery
Charger
Charges Single-Cell Li-Ion Batteries from Wall Adapter and USB Inputs with Automatic
Input Power Detection and Selection, 950mA Charger Current, Thermal Regulation, USB
Low Power Mode Select, C/X Charge Termination, 3mm × 3mm DFN Package
Dual Input Standalone Li-Ion Battery
Charger
Charges Single-Cell Li-Ion Batteries from Wall Adapter and USB Inputs with
Automatic Input Power Detection and Selection, 950mA Charger Current, Thermal
Regulation, Programmable USB Low Power Mode, C/10 Charge Termination,
3mm × 3mm DFN Package
PowerPath and ThinSOT are trademarks of Linear Technology Corporation.
35501f
LT 1205 • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
24
●
●
© LINEAR TECHNOLOGY CORPORATION 2005
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
相关型号：
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LTC3550 - Dual Input USB/AC Adapter Li-Ion Battery Charger with 600mA Buck Converter; Package: DFN; Pins: 16; Temperature Range: -40°C to 85°C
Linear
LTC3550EDHC-1#TRPBF
LTC3550-1 - Dual Input USB/AC Adapter Li-Ion Battery Charger with 600mA Buck Converter; Package: DFN; Pins: 16; Temperature Range: -40°C to 85°C
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