Bidirectional 2A charge/backup controller for supercapacitors

June 16, 2015 // By Graham Prophet
LTC3110 is a bidirectional, programmable input current buck-boost supercapacitor charger with active charge balancing for 1- or 2-series supercapacitors. The proprietary low noise buck-boost topology does the work of two separate switching regulators, saving size, cost and complexity.

LTC3110 operates in two modes, backup and charge mode. In backup mode, the device maintains a system voltage, VSYS, of 1.71V to 5.25V, powered from the supercapacitor stored energy. The supercapacitor storage input, VCAP, features a wide practical operating range from 5.5V down to 0.1V. This ensures that all practical stored supercapacitor energy is utilised, extending backup times or shrinking the storage capacitors.

Alternatively, in charge mode when the main power system is active, the LTC3110 can autonomously or through user command reverse the direction of power flow using the regulated system voltage to charge and balance the supercapacitors. VCAP is efficiently charged to above or below VSYS by the buck-boost PWM (pulse width modulator). The device also features a charge-mode average input current limit that can be programmed up to 2A with ±2% accuracy, preventing system power source overload while minimizing capacitor recharge time.

Active charge balancing eliminates the constant drain of dissipative external ballast resistors, ensuring charging even with mismatched capacitors, and less frequent recharge cycles. Programmable maximum capacitor voltage regulation actively balances and limits the voltage across each capacitor in the series stack to one-half of the programmed value, ensuring reliable operation as capacitors age and develop mismatched capacities. The low RDS(ON), low gate charge, synchronous switches provide high efficiency conversion to minimise the charging time of storage elements. The LTC3110 is ideal for safely charging and protecting large capacitors in backup power applications such as servers and RAID systems, and RF systems with battery/capacitor backup.