DESCRIPTION
The LTC®4425 is a constant-current/constant-voltage linear charger designed to charge a 2-cell supercap stack from either a Li-Ion/Polymer battery, a USB port, or a 2.7V to 5.5V current-limited supply. The part operates as an ideal diode with an extremely low 50mΩ on-resistance making it suitable for high peak-power/low average power applications. The LTC4425 charges the output capacitors to an externally programmed output voltage in LDO mode at a constant charge current, or to VINin normal mode with a smart charge current profile to limit the inrush current until the VINto VOUT differential is less than 250mV. In addition the LTC4425 can be set to clamp the output voltage to 4.9V or 5.4V.

FEATURES
■ 50mΩ Ideal Diode from VIN to VOUT
■ Smart Charge Current Profi le Limits Inrush Current
■ Internal Cell Balancer (No External Resistors)
■ Programmable Output Voltage (LDO Mode)
■ Programmable VIN to VOUT Current Limit
■ Continuous Monitoring of VIN to VOUT Current via
   PROG Pin
■ Low Quiescent Current: 20μA
■ VIN Power Fail, PGOOD Indicator
■ 2.45V/2.7V Cell Protection Shunts
   (4.9V/5.4V SuperCap Max Top-Off Voltage)
■ 3A Peak Current Limit, Thermal Limiting
■ Tiny Application Circuit, 3mm × 3mm × 0.75mm DFN
   and 12-Lead MSOP Packages

APPLICATIONS
■ High Peak Power Battery/USB Powered Equipment
■ Industrial PDAs
■ Portable Instruments/Monitoring Equipment
■ Power Meters, SuperCap Backup Circuits
■ PC Card/USB Modems