Programmable Supercap chargers have automatic cell balancing - Embedded.com

Programmable Supercap chargers have automatic cell balancing

The latest in a family of 2-cell supercapacitor chargers from Linear Technology Corp. are for addressing high peak power, data backup and 'dying gasp' needs in portable and data storage applications.  

The LTC3625/LTC3625-1 have a high efficiency switchmode topology which includes an internal buck converter between VIN and the series capacitor mid-point VMID to regulate the voltage on the bottom capacitor, as well as an internal boost converter between VMID and VOUT to regulate the voltage across the top capacitor.

The devices can charge two supercapacitors in series from a 2.7V to 5.5V current-limited supply to a pin-selectable output voltage (4.8V/5.3V for LTC3625 or 4V/4.5V for LTC3625-1).

The output current of the LTC3625/-1's buck converter is user-programmable via the PROG pin, and the input current of the boost converter is set at 2A (typical). The resulting maximum charge current is 1A continuous with two inductors, and 500mA with a single inductor configuration.

Each capacitor is protected against overvoltage by internal voltage clamps (2.4V/2.65V selectable for LTC3625 or 2.0V/2.25V selectable for the LTC3625-1).

The LTC3625/-1’s automatic cell balancing feature maintains approximately equal voltages across both cells, eliminating the need for balancing resistors while protecting each supercapacitor from overvoltage damage.

The LTC3625 and LTC3625-1 operate with a 50uA quiescent current when the output voltage is in regulation. When the input supply is removed or the EN pin is low, the LTC3625/-1 automatically enters a low current state, drawing less than 1uA from the supercapacitors.

The basic charging circuit requires only three external components (one inductor, one bypass capacitor at VIN and one programming resistor) and is highly compact, offered in a tiny 12mm2 package footprint.

Additional protection features include over-temperature protection for momentary overload conditions, over-current limiting, and reverse- current protection in which the device will continue to regulate at its programmed current even into a grounded output.

The LTC3625 and LTC3625-1 are available in a compact, thermally enhanced, 12-lead, low-profile (0.75mm) 3mm x 4mm DFN package. The devices are specified over a -40°C to 125°C operating junction temperature range.

Prices start at $3.00 for E grade and $3.45 for I grade each in 1,000-piece quantities.

Linear Technology

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