The LTC3351 is a backup power controller that charges and monitors a series stack of one to four supercapacitors. The LTC3351’s synchronous step-down controller drives N-channel MOSFETs for constant current/constant voltage charging with programmable input current limit. In addition, the step-down converter runs in reverse as a step-up converter to deliver power from the supercapacitor stack to the backup supply rail. Internal balancers eliminate the need for external balance resistors and each capacitor has a shunt regulator for overvoltage protection.The LTC3351 monitors system voltages, currents, stack capacitance and ESR which can all be read over the I2C/SMBus port. The hot swap controller uses N-channel MOSFETs for inrush control and a low loss path from the input to the output. The ideal diode controller uses an N-channel MOSFET for a low loss power path from the supercapacitors to the output. The LTC3351 is available in a thermally enhanced low profile 44-lead 4mm × 7mm × 0.75mm QFN surface mount package.APPLICATIONSSwappable PCIE Cards with NVMHigh Current 12V Ride-Through UPSServers/Mass Storage/High Availability Systems