L6924U datasheet(27/38 Pages) STMICROELECTRONICS

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L6924U

Application information: monitoring and protection

27/38

Considering typical values for NTC0°C and NTC50°C, the hysteresis is:

Equation 22

And:

Equation 23

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 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

HYS

051

900

780

900

≅

−

HYS

039

225

248

225

−

≅

−

= MAXCH

DETECT

L6924U Datasheet(PDF) 27 Page - STMicroelectronics