L9779WD datasheet(71/170 Pages) STMICROELECTRONICS

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L9779WD

Functional description

169

Figure 44. Ignition-pre drivers (IGN1 to 4) diagram

6.11.2

Ignition pre-driver diagnosis

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

according to Table 28: Fault encoding condition).

The detected faults are:



IGNx short circuit to battery (SCB)



IGNx open load (OL)



IGNx short to GND (SCG)

Short to GND

This diagnosis is made in two different ways based on the status of IGN_DIA_SGEN.

If IGN_DIA_SGEN = 1

When the IGNx is on, if for a time longer than Tign_filt, the current is bigger than IOVC, the

short to GND fault is detected and the IGNx output becomes high impedance, the fault is

latched and is reset at every Read Diag operation.

If IGN_DIA_SGEN = 0

When the IGNx is on, if for a time longer than Tign_filt, the voltage of IGNx is lower than

VLVT, the short to GND fault is detected and the IGNx output becomes high impedance, the

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

The high impedance is removed and IGNx is driven by the command:

–

after a Read Diag operation

–

if command is switched OFF and ON again.

Open load

When IGNt is on, if for a time longer than Tign_filt, the current is below Iol the open-load

fault is detected, latched and it is reset at every Read Diag operation. IGNx remains always

driven.

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