DESCRIPTION
The LTC4055 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.
FEATURES
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 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
APPLICATIONS
Portable USB Devices: Cameras, MP3 Players, PDAs
TYPICAL APPLICATION
High Power/Full Charge RPROG= RCLPROG= 100k
Simplified Block Diagram—PowerPath
Input and Battery Currents as a Function of Load Current
NTC Circuits
(3a)
(3b)
