The LTC4425 is the latest in Linear Technology’s family of two-cell supercapacitor chargers for high peak power, data backup, and “dying gasp” needs in portable and data storage applications. It uses a linear CC-CV architecture with thermal limiting to charge two supercaps in series to a programmable output voltage from a lithium-ion/polymer battery, a USB port, or other 2.7- to 5.5-V current-limited supply.

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The device features two operating modes: charge current profile (normal) and low-dropout (LDO). Its charge current profile mode charges the top of the supercap stack to the input voltage VIN with a charge current that varies inversely with the input-to-output voltage differential to prevent excessive heating. The LDO mode charges the stack to an externally programmed output voltage with a fixed charge current that’s also extremely programmable, Linear says. The charge current is resistor programmable up to 2 A (3 A peak). Internal shunts (2.45/2.7 V selectable) protect each capacitor against overvoltage.

The LTC4425’s onboard current-limited ideal diode’s 50-Ω on resistance prevents VIN back-driving, suiting the device for a variety of high-peak-power battery-powered and USB-powered equipment, power meters, supercap backup circuits, and PC card/USB modems. Its automatic cell balancing maintains equal voltages across both cells, eliminating the need for balancing resistors while protecting each supercap from overvoltage damage while minimizing current drain on the capacitors. 

The IC operates with a very low 20-µA quiescent current when the output voltage is in regulation and draws only 2 µA in shutdown from VIN or VOUT, whichever is higher. The basic charging circuit requires only six external components and is highly compact, offered in a 9-mm2 package footprint as well as a leaded package. Other features include a VIN power-fail indicator and continuous monitoring of VIN to VOUT current via the PROG pin. And, current and thermal limiting reduce charge current in cases of excessive temperature.

The LTC4425 is available in two compact, thermally enhanced packages: a 12-lead, low-profile (0.75 mm), 3- by 3-mm dual flat no-lead (DFN) package and a 12-lead mini small-outline package (MSOP). Operation from –40°C to 85°C is guaranteed. In stock, pricing starts at $2.25 each in 1000-piece quantities.

Linear Technology Corp.