DESCRIPTION
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 blocking, undervoltage lockout and thermal shutdown.

FEATURES
■ 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 PowerPathTM 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