Linear Technology/Analog Devices’ LTC3351 is a synchronous step-down controller that charges and monitors up to four supercapacitors at one time. This converter drives N-channel MOSFETs for constant current/constant voltage charging with programmable input current limit. In addition, the device 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. This device comes in a 44-pin QFN package that has an operating temperature of -40°C to +125°C. The LTC3351 is designed for hot swappable applications such as PCIe cards, high current UPS systems, and servers.