L9952XP datasheet(19/68 Pages) STMICROELECTRONICS

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L9952GXP

Description

Doc ID 13518 Rev 5

19/68

2.10

Fail safe output

After power-on (Vs > VPOR) or wakeup from VBAT -standby mode, the output FSO is set to

“HIGH”, if V1 is above the V1 threshold. FSO is set to “LOW” in case of V1 under voltage or

watchdog failure.

During V1-standby mode, FSO is HIGH unless a V1 under-voltage or watchdog reset

occurs. WD remains enabled in V1 standby mode until IV1 drops below 150uA. In VBAT -

standby mode, FSO is low. At exit from VBAT - standby mode, it goes to high as soon as V1

is stable.

At wakeup FSO remains high, provided that the watchdog is triggered successfully. It is set

low if the watchdog is not served during the long open window of if a V1 under-voltage

occurs.

Figure 5.

FSO

2.11

Reset – generator

IF V1 is turned on and the voltage exceeds the V1 reset threshold, the reset output

“NRESET” is switched to “HIGH” after a 2ms reset delay time. This is necessary for a

defined start of the micro controller when the application is switched on.

As soon as an under voltage condition of the output voltage (V1 < VRT) for more than 8us

appears, the reset output is switched low again.

Figure 6.

NReset

FSO = 0

Vbatstdby Mode

V1 undervoltage

Watchdog Failure

TSD2

NReset = 0

V1 Undervoltage

Wake-up Event 1)

1) Only if

(INT_en = 0) and (wake-up by WU-input or High Side Open Load)

Vpwm2 < 9V

(Exit Flash Mode)

Watchdog

Failure

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