L6924D datasheet(28/38 Pages) STMICROELECTRONICS

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Application information: monitoring and protection

L6924D

28/38

If a PTC connected to GND is used, the selection is the same as above, the only difference is

when the battery temperature increases, the voltage on the TH pin increases, and vice versa.

For applications that do not need a monitor of the battery temperature, the NTC can be

replaced with a simple resistor whose value is one half of the pull-up resistor RUP.

In this case, the voltage at the TH pin is always inside the voltage window, and the charge is

always enabled.

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

de-glitch time, a detection current IDETECT, equal to 1mA, 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 VABS (the value is VOPRGTH-50mV). If the battery

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

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

Figure 22. Battery absent detection flow chart

= MAXCH

DETECT

Eq: 9-13

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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