Power Electronics

Power Manager Charges Portable USB Devices

Linear Technology’s LTC4089 and LTC4089-5 each feature an autonomous power manager, ideal diode controller and standalone high-voltage switching battery charger for portable USB devices. Their switching topology accommodates various inputs including sources up to 36 V (40 V max).

The LTC4089/-5 feature PowerPath control that provides power to the USB peripheral device and charges the peripheral's single-cell lithium battery from the USB bus or a wall adapter power supply. It also allows for instant-on operation even with a depleted or missing battery. To comply with USB current-limit specifications, the LTC4089/-5 automatically reduces battery charge current as the system load current increases. To ensure that a fully charged battery remains topped off when the bus is connected, the ICs direct power to the load through the USB bus rather than extracting power from the battery.

Once all power sources are removed, current flows from the battery to the load through an internal 200-mΩ “ideal” diode, minimizing voltage drop and power dissipation. Onboard circuitry is provided to drive an optional external PFET to reduce the overall ideal diode impedance below 50 mΩ.

The LTC4089's switching regulator features Bat-Track adaptive output control, which greatly improves the efficiency of its 1.2-A battery charger as the switching regulator's output voltage automatically tracks the battery voltage. The LTC4089-5 provides a fixed 5-V output from the high-voltage input to charge single-cell Li-ion/Li-polymer batteries. The battery charger's float voltage is preset at 4.2 V with 1.0% accuracy.

Total charge time for charge termination is programmed by an external capacitor, and a C/10 charge current detection output is provided. Additional functions include thermal regulation, an NTC thermistor input for temperature-qualified charging, automatic recharging of the battery, reverse current blocking, and under-voltage lockout. The LTC4089/-5 is housed in a 22-pin, 6-mm x 3-mm x 0.75 mm DFN package. Pricing for 1000-pieces starts at $2.95 each.

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