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Supercapacitor charger targets short-term backup power

Posted: 29 Jul 2011 ?? ?Print Version ?Bookmark and Share

Keywords:supercapacitor? charger? PowerPath controller?

Linear Technology Corp. has rolled out 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 uses a low-noise dual mode (1x/2x) charge-pump architecture with constant input current to charge two supercapacitors in series from a 2.5每5.5V input supply to a programmable capacitor charge voltage between 2.5每5.3V. The charge current is resistor-programmable up to 150mA.

The LTC3226'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. The 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 with the charge pump staying 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 two amperes of backup current may be provided from the supercapacitor through the internal LDO.

The LTC3226 operates with a very low 55?A quiescent current when the VOUT is regulated. The basic charging circuit requires few external components and takes up little space. 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.

The LTC3226 is housed in a compact 16-lead, low-profile (0.75mm) 3 x 3mm QFN package, with operation from -40∼C 每125∼C. Pricing for the E and I grade devices starts at $2.67 and $3.07 each, respectively, in 1,000-piece quantities.

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