L9779WD datasheet(67/170 Pages) STMICROELECTRONICS

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L9779WD

Functional description

169

6.10

LSa, LSb, LSc, LSd diagnosis

Each channel locally detects and writes its own fault or no-fault condition (codified on 2 bit

according to the table FAULT ENCODING CONDITION).



short circuit to battery or overcurrent for all the outputs during ON condition.



open load or short to GND during OFF condition.

The faults are latched and reset every Read Diag operation.

In OFF condition the first fault detected is latched and can be overwritten only by the ON

condition fault.

Channel “on”

Short to Vb:

Current diagnosis is the result of a comparison between driver load current and internal

IOVC thresholds.

If: ILOAD > IOVC for t > TFILTEROVC the driver is switched off and the fault is set, latched and

reset every Read Diag operation.

When the fault occurs the driver is switched off with a controlled slew-rate.

The driver switches on AGAIN in the following conditions:

–

If command goes LOW and then HIGH again

–

If command remains active the driver is switched automatically on at every Read

Diag operation.

Short to GND:

Not available.

Open Load:

Not available.

Channel “off”

Short to Vb:

Not available.

Short to GND & open load:

In open load condition an internal circuit drives the OUTx voltage to VOUTOPEN with a

maximum pull-up/down current of IOUT_PU and IOUT_PD.

Diagnosis is done comparing driver output voltage with internal voltage thresholds VHVT

and VLVT: if the voltage is below VLVT a short to GND is detected, if the voltage is above

VLVT and below VHVT an open load is detected and if the voltage is above VHVT no fault is

present.

Diagnosis status is masked for Td_mask time after the off event occurs to allow the output

voltage to reach the proper value.

Short to GND and open load are filtered with TFILTERdiagoff time.

Diag status is latched and reset at every Read Diag operation.

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