Rainbow Electronics MAX1874 - Manual (Page 14)

MAX1874
Dual-Input, USB/AC Adapter, 1-Cell
Li+ Charger with OVP and Thermal Regulation
14 ______________________________________________________________________________________
MAX1874
USB INPUT
OVP UP TO 18V
CHARGING UP TO 6.0V
C5
4.7 µF
25V CERAMIC
C1
4.7 µF
6.3V CERAMIC
C4
2.2 µF
10V CERAMIC
C3
2.2
µF
6.3V CERAMIC
C6
0.1
µF
10V CERAMIC
DCLV
GND
BATT
NTC
THERMISTOR
10k
Ω AT +25°C
PON
REF
THRM
DC
USB
400m Ω
250m Ω Li+
CELL
USEL
500mA
100mA
EN
DCI
PGND BYP
REGULATOR
UOK
CHG
C2
1 µF
10V CERAMIC
DCOK
R4
10k
Ω
R2
1k Ω
D1
500mA,
SCHOTTKY
(MBR0520L)
Q2
FDN302
0.055 Ω, -20V
Q1
FDN302
0.055 Ω, -20V
TO REF
R5
100k Ω
R6
301k Ω
D2
500mA,
SCHOTTKY
(MBR0520L)
TO SYSTE
LOAD
Q3
FDN302
0.055
Ω, -20V
R3
10k Ω
Figure 4. Full-Featured Circuit. Overvoltage protection MOSFET (Q2) on DC withstands up to 18V from the AC adapter, but disables
charging at inputs over 6.2V. Output switch-over MOSFET (Q3) disconnects the battery from the system load when input power is
applied. The input can power the system through D1, D2, Q1, and Q2 when either USB or AC power is present.