MCP73871 Demo Board with Voltage Proportional Current Control User’s Guide
DS51812B-page 16 © 2009 Microchip Technology Inc.
2.3.4 Temperature Monitoring Option
The MCP73871 device monitors continuously the battery temperature during a charge
cycle by measuring the voltage between the THERM and V
SS
pins. An internal current
source provides the bias for most common 10 k negative-temperature coefficient
thermistors (NTC). The MCP73871 device compares the voltage at the THERM pin to
factory set thresholds of 1.24V and 0.25V, typically. Once a voltage outside the
thresholds is detected during a charge cycle, the MCP73871 device immediately
suspends the charge cycle, by turning off the charge and holding the timer value. The
charge cycle resumes when the voltage at the THERM pin returns to the normal range.
To activate this feature, remove R6 resistor and connect a 10 k NTC thermistor to TP6
and TP7 test points.
FIGURE 2-5: MCP73871 Charge Profile in Constant Voltage Mode for a
900 mAh Li-Ion Cell.
0
1
2
3
4
5
0 25 50 75 100 125 150
Time (min)
Battery Volatge (V)
Cell Temperature / 10
(°C)
0
0.2
0.4
0.6
0.8
1
Charge Current (A)
V
BAT
Cell Temperature / 10
I
Charge
