A high efficiency input current-limited buck-boost supercapacitor charger has been released by Linear Technology Corporation with active charge balancing for 1 or 2 
series supercapacitors. This new device is the LTC3128 and features an average input current limit that can be programmed up to 3A with +/-2 percent accuracy, preventing power source overload while minimising capacitor recharge time.
The device feature highly efficient active charge balancing that eliminates dissipative external ballast resistors, ensuring balanced operation and charging with mismatched capacitors, and less frequent recharge cycles.
Design features include a programmable maximum capacitor voltage clamp that actively monitors and enforces the voltage across each capacitor in the series stack, this aims to ensure reliable operation as capacitors age and develop mismatched capacities.
The company points out that the low noise buck-boost topology allows the output supercapacitor to be charged whether above or below the input. The low-RDS(on), low gate charge synchronous switches can provide high efficiency conversion to minimize the charging time of storage elements. This makes the LTC3128 ideal for safely charging and protecting large capacitors in backup power applications.
The input current limit and maximum capacitor voltage are each programmed using a single resistor. Average input current is accurately controlled over a 0.5A to 3A programming range, and the individual maximum capacitor voltage can be set from 1.6V to 3.0V.
Other features include <1µA quiescent current from VOUT in Burst Mode operation, accurate power good and power failure indicators, and thermal overload protection.
The device is housed in compact, thermally enhanced 4mm by 5mm QFN and 24-lead TSSOP packages, both featuring operation from -40°C to 125°C.
Linear Technology Corporation
www.linear.com/product/LTC3128
