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LOW-COST DOUBLE LI-ION BATTERY CHARGER USING ST6255C/ST6265C MCU

Figure 5. Thermistor Voltage Indication

Table 3. Thermistor Voltage Thresholds used by the Evaluation Board

the table above is only an example. Note that, generally, for this kind of batteries, the temperature

limit is set to 45°C.

2.4 MCU SOFTWARE

2.4.1 Architecture

The software provided with the evaluation board has a state machine architecture. As ex-

plained further, 10 charging states can be defined for each slot. Each slot is driven by its state

machine, with some interactions to implement front slot priority.

In order to measure the charge time, a timekeeper is implemented and counters are incre-

mented periodically.

Most of the time, slot states are unchanged. This implies that the PWM duty cycle, charge en-

able signals and LED on/off states are constant. Periodically, the ST6 measures battery cur-

rent, battery voltage and thermistor voltage for both slots. Using the measurements and the

timekeeper values, it updates slot states and the output configuration. If necessary, it resets

the timekeeper.

Symbol

Meaning

Value

Unit

Battery Detection Voltage

4.7

V

Overheat Voltage

2.0

battery under normal

temperature conditions

no battery

battery under overheat