Preliminary

Datasheet

LP4062

LP4062 –00

Ver. 1.0 Datasheet

Nov.-2007

Page 12 of 13

USB and Wall Adapter Power

The LP4062 allows charging from both a wall adapter and a

USB port. Figure 12 shows an example of how to combine

wall adapter and USB power inputs. A P-channel MOSFET,

MP1,is used to prevent back conducting into the USB port

when a wall adapter is present and a Schottky diode, D1, is

used to prevent USB power loss through the 1k pull-down

resistor. Typically a wall adapter can supply more current than

the 500mA-limited USB port. Therefore, an N-channel

MOSFET, MN1, and extra 10k program resistor are used to

increase the charge current to 800mA when the wall adapter is

present.

Layout Considerations

Follow the PCB layout guidelines for optimal performance of LP4062.

For the main current paths as indicated in bold lines, keep their traces short and wide.

Put the input capacitor as close as possible to the device pins (VIN and GND).

Connect all analog grounds to a command node and then connect the command node to the power

ground behind the output capacitors.

Output not connect loading when charging

LP4062