The LTC4425 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 VOUTdifferential is less than 250mV. In addition the LTC4425 can be set to clamp the output voltage to 4.9V or 5.4V.Charge current (VOUTcurrent limit) is programmed by connecting a resistor between PROG and GND. The voltage on the PROG pin represents the current fl owing from VINto VOUTfor current monitoring. An internal active balancing circuit maintains equal voltages across each supercapacitor and clamps the peak voltage across each cell to a pin-selectable maximum value. The LTC4425 operates at a very low 20μA quiescent current (shutdown current <3μA) and is available in a low profile 12-pin 3mm × 3mm DFN or a 12-lead MSOP package.ApplicationsHigh Peak Power Battery/USB Powered EquipmentIndustrial PDAsPortable Instruments/Monitoring EquipmentPower Meters, SuperCap Backup CircuitsPC Card/USB Modems