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LTC3625/LTC3625-1 Chargers - .PDF file.

Linear Technology has introduced two new two-cell supercapacitor chargers for addressing high peak power, data backup and ‘dying gasp’ needs in portable and data storage applications.

The LTC3625 and the LTC3625-1 deliver high-efficiency switch-mode topology that 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 2.7-5.5V current-limited supply to a pin-selectable output voltage (4.8V/5.3V for the LTC3625 or 4V/4.5V for the LTC3625-1).

These ICs provide fast capacitor charge times, according to the company.

The combination of high efficiency, high charge current, low quiescent current and low minimum external part counts makes the devices ideal for small-form-factor backup or high peak power systems, USB-powered equipment, industrial personal digital assistants, portable instruments and monitoring equipment, power meters, supercap backup circuits and PC cards/USB modems.

The output current of the devices’ buck converters 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 the LTC3625 or 2.0V/2.25V selectable for the LTC3625-1).

The 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 the LTC3625-1 operate with a very low 50uA quiescent current when the output voltage is in regulation.

When the input supply is removed or the EN pin is low, the devices automatically enter 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 12mm2 package footprint.

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

The LTC3625 and the LTC3625-1 are available in compact, thermally enhanced, 12-lead, low-profile (0.75mm) 3 x 4mm DFN packages.

The devices are specified over a -40C to +125C operating junction temperature range and are in stock, with prices starting at USD3.00 (GBP1.90) for E grade and USD3.45 for I grade each in 1,000-piece quantities.

Linear Technology now part of Analog Devices

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