USB power pack is compact

01 June 2006

Two devices from Linear Technology (www.linear.com) incorporate and autonomous power manager, diode controller and standalone, high voltage switching battery charger for portable USB devices. The
LTC4089 switching regulator and LTC4089-5 are both housed in a low-profile, 0.75mm, 22pin, 6 x 3mm DFN package.

They have a switching topology to accommodate inputs from 36V (40V max) such as 12V DC/DC wall adapters, FireWire ports or automotive batteries. They also accept low voltage sources, such as 5V wall adapters or USB inputs and single cell, Li-Ion-polymer batteries.

The LTC4089-5 has the company’s PowerPath control to provide power to the USB bus or wall adapter power supply. It also enables instant-on operation, even if the battery is depleted or absent. The devices comply with USB current limit specifications and automatically reduce battery charge current as the system load current increases.

The IC directs power to the load through the USB bus rather than from the battery to ensure that a fully-charged battery remains topped off when the bus is connected. Current flows from the battery to the load through an internal 200m2 low loss ideal diode, to minimise voltage drop and dissipation when all power sources are removed. Onboard circuitry is provided to drive an optional external PFET to reduce the overall ideal diode impedance below 50m2.

The LTC4089 has Bat-Track adaptive output control, which automatically controls the battery voltage to improve the 1.2A-capable battery charger’s efficiency. The LTC4089-5 provides a fixed 5V output fromt eh high voltage input to charge single cell batteries. The float voltage is pre-set at 4.2V, with guaranteed
accuracy from 0 to 85°C.


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