New Industry Products

# Linear Tech Introduces 150mA Supercapacitor Charger with PowerPath Control & Auto Cell Balancing

July 28, 2011 by Jeff Shepard

Linear Technology Corp. introduced the LTC3226, an inductorless supercapacitor charger with backup PowerPath™ controller for Li-ion or other low-voltage system rails in applications that require short term backup power. The device employs a low-noise dual mode (1x/2x) charge-pump architecture with constant input current to charge two supercapacitors in series from a 2.5 to 5.5V input supply to a programmable capacitor charge voltage between 2.5 and 5.3V. Charge current is resistor-programmable up to 150mA. 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 VIN to VOUT 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 VOUT load current from the stored supercapacitor charge while the external ideal diode prevents reverse current flow into VIN. Up to 2A of backup current may be provided from the supercapacitor through the internal LDO.

The LTC3226 operates with a very low 55µA 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 tiny 3 x 3mm QFN package. The device’s high 900kHz 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, VOUT or CPO pins to ground. Other features include CAP PGOOD and VIN PFO (power fail) outputs as well as a VOUT RST output for system housekeeping.

Housed in a compact 16-lead, low-profile (0.75mm) 3 x 3mm 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.