Datasheet

14
LTC4054-4.2/LTC4054X-4.2
405442xf
USB and Wall Adapter Power
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, 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 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
+
LTC4054-4.2
BAT
PROG
V
CC
D1
5V WALL
ADAPTER
600mA I
CHG
USB POWER
500mA I
CHG
I
CHG
SYSTEM
LOAD
Li-Ion
BATTERY
MP1
1k
10k
2k
MN1
4
3
5
405442 F07
APPLICATIO S I FOR ATIO
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