UM1693 datasheet(53/196 Pages) STMICROELECTRONICS

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UM1693

Usage/handling of fault reset and standby

195

temperature and high battery voltage, may trigger the power limitation, leading to latch-off of

the HSD. In consequence the load will not be turned on. Even though the device could be

restarted again by toggling FaultRST pin low for a time longer than tLATCH_RST, so that all

latches are reset, the latch will occur again as long as the device is maintained in latch-off

mode.

A possible way to overcome this issue is managing the FaultRST pin in such a way that the

latch-off functionality is blanked out for a time longer than the time of the inrush of the bulb.

The following figure is giving an example, on how the correct turn-on of an incandescent

bulb is ensured by means of a 20 ms blanking pulse on FaultRST pin. Despite the device

toggles in Power Limitation for approximately 10 ms, the load is correctly activated with

negligible delay.

Figure 31. FR handling example - bulb inrush blanking (VNQ7140AJ-E)

Even more, the FaultRST pin can be managed as a global system pin, connecting this pin of

several high-side drivers in parallel to a specific microcontroller I/O port (refer to example in

Figure 32 and Section 8.1: Paralleling of logic input pins for advice on how to parallel pins).

This signal is always kept high, means all connected devices are configured in latch-off

mode, except

•

For a periodical “unlatch” pulse for duration longer than tLATCH_RST max, once per

diagnostic period. This “unlatch” pulse aims at restarting all latched channels, which

are supposed to be restarted, i.e. when the debouncing strategy for short circuit

detection is not yet elapsed.

•

For a blanking pulse (FaultRST low for i.e. 10 ms) generated at every activation of any

channel.

Figure 33 illustrates the described FaultRST pin handling concept.

GAPG1122131113MS

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UM1693 Datasheet(PDF) 53 Page - STMicroelectronics