M
Switch-Mode 1-Cell Li+ Chargers
8
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Pin Description
PIN
NAME
FUNCTION
1
CHG
Charge Status LED Driver. Open-drain LED driver sinks 10mA when the MAX1925/MAX1926 are charging.
CHG
also blinks at a 0.5Hz rate during fault states (see the
Timing
section). High impedance when charger is
in shutdown. See Tables 1 and 2.
2
EN
Enable. Drive EN high to enable charger. Logic level input for normal ON/OFF control. In the MAX1926 EN is
internally pulled up to 3V with a 300k
resistor.
3
THRM
Thermistor Input. Monitors external thermistor (10k
at +25
°
C). When external temperature is lower than 0
°
C
or above +50
°
C, charging stops and the charger enters fault mode. Charging resumes when the temperature
returns to normal. During a temperature fault the MAX1926 blinks the
CHG
output, while MAX1925
CHG
remains off (high).
4
ACON
Power-OK Indicator Output. Open-drain output goes low when AC adapter power is valid. See Table 2 for
ACON
states.
Timing Capacitor Connection. Connect timer cap to program full-charge safety timeout interval and
prequalification fault times. Timeouts with C
CT
= 100nF are:
Full Timer (t
FULLCHG
): 3 hours
—
If FASTCHG is not completed within this time a fault is asserted.
Prequal2 Timer: Full Timer/17 (10.67 min)
Prequal1 Timer: Full Timer/1088 (10s)
Charge-Current Sense Input. 142mV nominal regulation threshold. CS is high impedance during shutdown.
Battery-Sense Input. Also negative side of charge-current sense. BATT is high impedance during shutdown.
Ground
Power Ground
5
CT
6
7
8
9
CS
BATT
GND
PGND
10
EXT
PMOS Gate-Driver Output. Drives gate of external PMOS switching transistor from IN to GND. When using the
MAX1926, ensure that the MOSFET V
GS
rating is greater than V
IN
.
Supply Voltage Input
Supply-Sense Input. Connect IN to INP.
11
12
INP
IN