Simple, Efficient, 1-Cell Li+ Pulse Charger
Typical Operating Characteristics
(V
IN
=
CHG
= +10V, V
BATT
= +4.2V, THERM = 10kΩ to GND, T
A
= +25°C, unless otherwise noted.)
MAX1879
NORMALIZED TIMER PERIOD
vs. AMBIENT TEMPERATURE
MAX1879 toc01
NORMALIZED BATTERY REGULATION
VOLTAGE vs. TEMPERATURE
NORMALIZED REGULATION VOLTAGE
1.0015
1.0010
1.0005
1.0000
0.9995
0.9990
0.9985
0.9980
0.9975
0.9970
NORMALIZED TO +25°C
MAX1879 toc02
PRECHARGE CURRENT
vs. INPUT VOLTAGE
8.8
PRECHARGE CURRENT (mA)
8.6
8.4
8.2
8.0
7.8
7.6
7.4
7.2
7.0
V
BATT
= 2V
V
BATT
= 0
MAX1879 toc03
1.020
1.015
NORMALIZED TIMER PERIOD
1.010
1.005
1.000
0.995
0.990
0.985
0.980
-40
-20
0
20
40
TEMPERATURE (°C)
60
80
NORMALIZED TO +25°C
1.0020
9.0
-40
-20
0
20
40
TEMPERATURE (°C)
60
80
5
10
15
V
IN
(V)
20
25
Pin Description
PIN
1
2
NAME
IN
GATE
FUNCTION
Input Voltage from Current-Limited Voltage Source (+22V max). Bypass to GND with a 0.1µF capacitor.
Gate Drive for External PMOS Pass Element. The PMOS device should have a V
GS
threshold less than
2.5V. See
Selecting External Components.
Charge Status Indication. A
CHG
low indicates that the MAX1879 is charging a battery.
CHG
goes high
when the on/off duty cycle falls to 1/8, indicating that the battery is charged to approximately 95% of full
capacity.
CHG
is an open-drain current-limited N-channel MOSFET suitable for directly driving an LED.
Connect a pullup resistor to the logic supply to generate a logic-level signal.
CHG
blinks at 2Hz during the
Prequalification state (2.2V < V
BATT
< 2.5V) and during a temperature fault.
Minimum ON/OFF Pulse Width Selection (Table 2)
Battery Regulation Voltage Adjustment. Bypass to GND with a 1000pF capacitor. Connect a resistor from
ADJ to GND to reduce the nominal +4.200V regulation set point. See
Adjusting the Battery Regulation
Voltage.
Ground. See
Layout Guidelines
for information on system grounding. Connect the battery’s negative
terminal to GND.
Thermistor Temperature-Sensor Input. Connect an NTC thermistor (10kΩ at +25°C) from THERM to GND to
allow prequalification of the cell temperature for fast-charge. Replace the thermistor with a 10kΩ resistor if
temperature sensing is not required.
Cell Voltage Monitor Input, Precharge Current Output, and MAX1879 Power Source. Connect BATT to the
positive terminal of a single Li+ cell. Bypass BATT with a capacitor to ground (1.5µF per amp of charge
current).
3
CHG
4
5
TSEL
ADJ
6
GND
7
THERM
8
BATT
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5
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
