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 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 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 and are in stock, priced starting at $3.00 for E grade and $3.45 for I grade each in 1,000-piece quantities. For more information, visit http://www.linear.com/3625.
Summary of Features: LTC3625 and LTC3625-1
* High Efficiency Step-Up/Step-Down Charging of Two Series Supercapacitors
* Automatic Cell Balancing Prevents Capacitor Overvoltage During Charging
* Programmable Charging Current Up to 500mA (Single Inductor), 1A (Dual Inductor)
* VIN = 2.7V to 5.5V
* Selectable 2.4V/2.65V Regulation per Cell (LTC3625), Final Output Voltage 4.8V/5.3V
* Selectable 2V/2.25V Regulation per Cell (LTC3625-1), Final Output Voltage 4V/4.5V
* Low No-Load Quiescent Current: 50uA
* IV>OUT, IVIN < 1uA in Shutdown * Low Profile 12-lead 3mm x 4mm DFN Package