LTC4054-4.2/LTC4054X-4.2
W U U
U
APPLICATIO S I FOR ATIO
USB and Wall Adapter Power
5V WALL
ADAPTER
The LTC4054 allows charging from both a wall adapter
and a USB port. Figure 7 shows an example of how to
combine wall adapter and USB power inputs. A P-channel
MOSFET,MP1,isusedtopreventbackconductingintothe
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.
I
CHG
600mA I
LTC4054-4.2
BAT
CHG
3
5
SYSTEM
LOAD
D1
USB POWER
4
V
CC
500mA I
CHG
MP1
+
PROG
10k
Li-Ion
BATTERY
1k
2k
MN1
405442 F07
Typically a wall adapter can supply more current than the
500mA-limitedUSBport.Therefore,anN-channelMOSFET,
MN1, and an extra 10k program resistor are used to
increase the charge current to 600mA when the wall
adapter is present.
Figure 7. Combining Wall Adapter and USB Power
405442xf
14
Linear [ Linear ]
