150-mA supercapacitor charger with auto cell balancing offers short term backup power
Charge current is resistor-programmable up to 150 mA. The device’s automatic cell balancing and voltage clamping features maintain equal voltages on both cells without requiring balancing resistors. This protects each supercapacitor from overvoltage damage that could otherwise be caused by mismatches in cell capacitance or leakage, while minimizing current drain on the capacitors.
The LTC3226 has two modes of operation: normal and backup. Operating mode is determined by a programmable power fail (PFI) comparator. In normal mode (PFI high), power flows from V IN to V OUT through a low loss external FET ideal diode, and the charge pump stays on to top off the supercapacitor stack. In backup mode (PFI low), the charge pump is turned off and the internal LDO is turned on to supply the V OUT load current from the stored supercapacitor charge while the external ideal diode prevents reverse current flow into V IN . Up to 2 A of backup current may be provided from the supercapacitor through the internal LDO.
The LTC3226 operates with a low 55 µA quiescent current when the output voltage is in regulation. The basic charging circuit requires few external components and takes up little space; the IC is offered in a 3 mm x 3 mm QFN package. The device’s 900 kHz operating frequency reduces the size of external components. Internal current limit and thermal shutdown circuitry allow the device to survive a continuous short-circuit from the PROG, V OUT or CPO pins to ground. Other features include CAP PGOOD and V IN PFO (power fail) outputs as well as a V OUT RST output for system housekeeping.
Housed in a compact 16-lead, low-profile (0.75 mm) 3 mm x 3 mm QFN package, the LTC3226 operates from -40 to 125°C. Pricing for the E and I grade devices starts at $2.67 and $3.07 each, respectively, in 1,000-piece quantities.
More information about the LTC3226 inductorless supercapacitor charger at www.linear.com/product/LTC3226