UB2017

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

11 of 13

www.unisonic.com.tw

QW-R502-868.a

APPLICATION INFORMATION(Cont.)

USB and Wall Adapter Power

The UTC UB2017 allows charging from both a wall adapter and a USB port. Figure 5 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 1kΩ pull-down resistor. Typically a wall adapter can supply more current than the 500mA-limited USB port.

Therefore, an N-channel MOSFET, MN1 and an extra 10kΩ program resistor are used to increase the charge

current to 600mA when the wall adapter is present.

Fig. 5 Combining Wall Adapter and USB Power