AN2390 datasheet(5/42 Pages) STMICROELECTRONICS

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AN2390

Theory of operation

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Theory of operation

1.1

Li-ion battery charging

Li-ion batteries have a constant current/constant voltage charging algorithm as shown in

Figure 2.

Li-ion battery charging

During Stage 1 (constant current charge), the charging current is kept at a constant value

(Iconst) until the battery voltage reaches the final cell voltage (VF). In Stage 2 (constant

voltage charge), the voltage is kept constant within this limit by slowly decreasing the

current. Charging is stopped when the current drops below the threshold value fixed by the

manufacturer (ISAT). This current indicates that the battery is saturated.

In some cases before stage 1, pre-charging can also be done if the battery is fully

discharged.

A failure condition occurs if even after a certain time (tFAIL) of fast charging, the battery

voltage remains particularly low (under VSC). In this case, charging is stopped and the

battery is isolated from the charger. The charger also indicates a battery failure without

waiting (protection against short-circuit) if battery current is higher than the threshold IFAIL

(equals to the maximum supply current).

If the charging time exceeds a certain expiration value (tEXP), charging is stopped even if the

battery is not yet saturated. As the tEXP value is greater than the tFAIL value, the charger

indicates that the battery is in good condition and fully charged.

Stage 1

Stage 2

Battery

current

voltage

Battery

ICONST

ISAT

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