Milpitas, Calif.—Linear Technology's LTC4085, a complete controller for portable power applications, integrates an autonomous power manager, "ideal diode" switch, and stand alone battery charger to provide seamless transition between USB input, wall adapter, and battery power sources.
The LTC4085 features the company's PowerPath architecture to deliver power to a USB powered peripheral device and charge the peripheral's single-cell lithium-ion battery from the USB port or a wall adapter. To comply with USB current limit specifications, the LTC4085 automatically reduces battery charge current as the system load current increases.
If the USB power source is removed, current flows from the battery to the load through an internal 200 milliohm low loss diode, minimizing voltage drop and power dissipation. On-board circuitry is provided to drive an optional external PFET hookup to reduce the overall "ideal" diode impedance below 50 milliohms.
The LTC4085 will detect the presence of a wall adapter and use it as an alternate power source to charge the battery while providing power to the system load. When powered from a wall adapter, the LTC4085 also allows charging the battery at a higher current (up to 1.5 amps) than specified by USB requirements (100/500 mA). Additional functions include a charge termination timer, automatic recharge, NTC thermistor input, automatic switchover to battery when the AC adapter input is removed, inrush current limiting, reverse current blocking, under-voltage lockout and thermal regulation.
The LTC4085's float voltage is preset at 4.2 volts with guaranteed 0.8 percent accuracy from 0 to +85°C. Charge current is programmed by an external resistor. For battery pre-conditioning and qualification, fully discharged cells are automatically trickle charged at 10 percent of the programmed current until the cell voltage exceeds 2.8 volts. Total charge time for charge termination is programmed by an external capacitor.
Click here for the device datasheet. The LTC4085, in a 14-pin, 3-by-3 DFN package and rated for operation over -40 to +85°C, is priced starting at $1.65 each in 1k pieces.
Linear Technology, 1-800-4LINEAR, www.linear.com