Programmable supercap charger achieves automatic cell balancing

Programmable supercap charger achieves automatic cell balancing

The LTC4425 two-cell supercapacitor charger addresses high-peak power, data backup and “dying gasp” needs in portable and data storage applications. It employs a linear CC-CV architecture with thermal limiting to charge two supercapacitors in series to a programmable output voltage from a Li-ion/polymer battery, a USB port, or other 2.7 to 5.5-V current-limited supply.

The charger features charge current profile (normal) and LDO operating modes. The device’s charge current profile mode charges the top of the supercap stack to VIN with a charge current that varies inversely with the input-to-output voltage differential in order to present excessive heating.

The LDO mode charges the stack to an externally programmed output voltage with a fixed charge current that is also externally programmable. Charge current is resistor programmable up to 2 A (3 A peak), and each capacitor is protected against overvoltage by internal shunts (2.45 or 2.7 V selectable).

The device has an onboard current-limited ideal diode that features 50-mΩ on-resistance to prevent back-driving of VIN ,. The automatic-cell-balancing feature maintains equal voltages across both cells, eliminating the need for balancing resistors while protecting each supercapacitor from overvoltage damage while minimizing current drain on the capacitors. The basic charging circuit requires only six external components offered in a 9-mm2 package footprint as well as a leaded package. ($2.25 ea/1,000 — available now.)

Linear Technology , Milpitas , CA
Sales Office 408-428-2050
http://www.linear.com