L6924UTR datasheet(27/37 Pages) STMICROELECTRONICS

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L6924U

Application information: monitoring and protection

Doc ID 14716 Rev 2

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8.2

Battery absence detection

This feature provides a battery absent detection scheme to detect the removal or the

insertion of the battery. If the battery is removed, the charge current falls below the IENDTH.

At the end of the de-glitch time, a detection current IDETECT, equal to 1 mA, is sunk from the

output for a time of TDETECT. The device checks the voltage at the output. If it is below the

VPRETH, a current equal to IDETECT is injected in the output capacitor for a TDETECT, and it is

checked to see if the voltage on the output goes higher than VRCH (4.05 V). If the battery

voltage changes from VPRETH to VRCH and vice versa in a TDETECT time, it means that no

battery is connected to the charger. The TDETECT is expressed by:

Equation 24

8.3

Status pins

To indicate various charger status conditions, there are two open-collector output pins, ST1

and ST2. These status pins can be used either to drive status LEDs, connected with an

external power source, by a resistor, or to communicate to a host processor.

Figure 20.

Battery absence detection flow chart

= MAXCH

DETECT

BATTERY

ABSENT

Detect Low Absent

VBAT

VPRETH

FAST CHARGE

Detect High Absent

VBAT

VRCH

PRE CHARGE

YES

DETECT LOW ABSENT = a ISINK is sunk for a TDET from the battery

DETECT HIGH ABSENT = a IINJ is injected for a TDET in the battery

TDET = 100ms (Typ.)

ISINK = IINJ = 1mA (Typ.)

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