Electrical Specifications Subject to Change
LTC4055
USB Power Controller
and Li-Ion Linear Charger
FEATURES
s
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DESCRIPTIO
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Charges Single Cell Li-Ion Batteries Directly from
USB Port
Load Dependent Charging Guarantees USB Input
Current Compliance
Automatic Battery Switchover When Input Supply
is Removed
Constant-Current/Constant-Voltage Operation with
Thermal Feedback to Maximize Charging Rate
Without Risk of Overheating
Selectable 100% or 20% Current Limit
(e.g., 500mA/100mA)
Low Loss Full PowerPath
TM
Control with Ideal Diode
Operation (Reverse Current Blocking)
Preset 4.2V Charge Voltage with 0.8% Accuracy
USB Compliant Suspend Mode
Programmable Charge Current and Termination Timer
Automatic Recharge
Soft-Start Limits Inrush Current
NTC Thermistor Input for Temperature Qualified
Charging
Tiny (4mm
×
4mm
×
0.8mm) QFN Package
The LTC
®
4055 is a USB power manager and Li-Ion battery
charger designed to work in portable battery-powered
applications. The part manages and limits the total current
used by the USB peripheral for operation and battery
charging. Depending on the state of the current select pin
(HPWR), total input current can be limited to either 100mA
or 500mA. The voltage drop from the USB supply or
battery to the USB peripheral is typically less than 100mV
at 400mA and 20mV at 80mA. Other management features
include: automatic switch over to battery when input is
removed, inrush current limiting, reverse current block-
ing, undervoltage lockout and thermal shutdown.
The LTC4055 includes a complete constant-current/con-
stant-voltage linear charger for single cell Li-ion batteries.
The float voltage applied to the battery is held to a tight
0.8% (typ) tolerance, and charge current is programmable
using an external resistor to ground. Fully discharged cells
are automatically trickle charged at 10% of the pro-
grammed current until the cell voltage exceeds 2.8V. Total
charge time is programmable by an external capacitor to
ground. When the battery drops 100mV below the float
voltage, automatic recharging of the battery occurs. Also
featured is an NTC thermistor input used to monitor
battery temperature while charging.
The LTC4055 is available in a 16-pin low profile
(4mm
×
4mm) QFN package.
APPLICATIO S
s
Portable USB Devices: Cameras, MP3 Players, PDAs
, LTC and LT are registered trademarks of Linear Technology Corporation.
PowerPath is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
5V (NOM)
FROM USB
CABLE V
BUS
IN1
1Ω
10µF
IN2
V
NTC
NTC
WALL
SHDN
SUSPEND USB POWER
500mA/100mA SELECT
SUSP
HPWR
TIMER PROG
0.1µF
600
OUT
BAT
TO LDOs,
REGs, ETC
500
400
CURRENT (mA)
+
10µF
Li-Ion
CELL
LTC4055
CHRG
ACPR
300
200
100
CLPROG
100k
GND
0
–100
100k
4055 TA01
0
U
High Power/Full Charge
R
PROG
= R
CLPROG
= 100k
I
IN
I
LOAD
I
BAT
CHARGING
100
200
300
400
I
LOAD
(mA)
500
600
I
BAT
(IDEAL DIODE)
4055 TA02
U
U
4055p
1
LINER [ LINEAR TECHNOLOGY ]
