Circuit description – Rainbow Electronics MAX8903A User Manual
Page 12
MAX8903A
2A 1-Cell Li+ DC-DC Charger for USB*
and Adapter Power
12
______________________________________________________________________________________
Circuit Description
The MAX8903A is a dual input charger with a 16V input
for a wide range of DC sources and USB inputs. The IC
includes a high-voltage (16V) input DC-DC step-down
converter that reduces charger power dissipation while
also supplying power to the system load. The step-
down converter supplies up to 2A to the system, the
battery, or a combination of both.
A USB charge input can charge the battery and power
the system from a USB power source. When powered
from USB or the DC input, system load current peaks
that exceed what can be supplied by the input are sup-
plemented by the battery.
The MAX8903A also manages load switching from the
battery to and from an external power source with an
on-chip 50m
Ω MOSFET. This switch also helps support
load peaks using battery power when the input source
is overloaded.
PG
PG
DC
DC
BST
LX
LX
CS
CS
SYS
SYS
BAT
BAT
FLT
UOK
DOK
FAULT
OUTPUT
USB PWR OK
DC PWR OK
TO VL
R
PU
4 x 100k
Ω
18
19
8
24
23
21
20
1
2
3
4
6
27
28
25
26
17
USB
ISET
IDC
R
ISET
R
IDC
DCM
THM
CEN
IUSB
GND
NTC
10k
Ω
USUS
5
9
16
12
CHARGE ON
OFF
100mA
500mA
USB SUSPEND
14
7
15
TO SYSTEM
LOAD
CHG
22
CHARGE
INDICATOR
C
DC
4.7
μF
CT
C
CT
0.15
μF
ADAPTER
VBUS
GND
C
BST
0.1
μF
L1
1
μH
13
11
C
USB
4.7
μF
USB
10
RT
10k
Ω
TO VL
1-CELL
LI+
C
BAT
10
μF
C
SYS
10
μF
VL
MAX8903A
Figure 2. Typical Application Circuit Using a Separate DC and USB Connector