Fast-charge, 3A buck-boost chip for supercaps

February 17, 2014 // By Graham Prophet
LTC3128 is a high efficiency, input current-limited buck-boost supercapacitor charger with active charge balancing for 1 or 2 series supercapacitors.

The LTC3128 features an average input current limit that can be programmed up to 3A with ±2% accuracy, preventing power source overload while minimising capacitor recharge time. Efficient active charge balancing removes the need to balance inter-cell charging by dissipating power in ballast resistors, ensuring balanced operation and charging with mismatched capacitors, and less frequent recharge cycles.

A programmable maximum capacitor voltage clamp actively monitors and enforces the voltage across each capacitor in the series stack, ensuring reliable operation as capacitors age and develop mismatched capacities. 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 provide high efficiency conversion to minimise the charging time of storage elements. This combination of features makes the LTC3128 suitable for safely charging and protecting large capacitors in backup power applications.

The LTC3128’s 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. The input voltage range is 1.72V to 5.5V and the output voltage range, 1.8V to 5.5V. Other features of the LTC3128 include less-than 1μA quiescent current from VOUT in Burst Mode operation, accurate power-good and power-failure indicators, and thermal overload protection. Efficiency of charge transferred to the supercap is up to 96%.

The device comes in a thermally-enhanced 4 x 5 mm QFN and 24-lead TSSOP packages, both featuring operation from -40 to 125C, for $3.95 (1,000).

Linear Technology;