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Maxim > Design Support > Technical Documents > Application Notes > Automotive > APP 2769
Keywords: battery charger, thermal protection, Li+, lithium ion, safety, set temperature limits, thermistor,
dual comparator, window comparator, battery charging
APPLICATION NOTE 2769
Dual Comparator Thermally Protects Li+ Battery
Dec 29, 2003
Abstract: A dual comparator and thermistor set safe temperature limits for a lithium-ion battery charging
circuit. The single-cell lithium-ion (Li+) battery charger can be powered from a USB port or external
supply.
Most manufacturers recommend that Li+ (lithium-ion) batteries not be charged below 0°C or above
+50°C. You can monitor both of these limits by adding a thermistor and dual (window) comparator to a
Li+ battery charger (Figure 1).
Figure 1.This lithium battery charger derives its power from from a USB port and provides thermal
protection for the battery.
The circuit has a low-temperature trip point of +2.5°C and a high-temperature trip point of +47.5°C. A
precision voltage reference is not necessary. Because the comparator resistor network is ratiometric,
variations in the supply voltage (V
BUS
) do not affect the trip thresholds.
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