L9788 datasheet(83/264 Pages) STMICROELECTRONICS

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DS12308 Rev 4

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L9788

Low-side drivers

263

Low-side drivers

Low-side drivers are used for power stages driving and they include:



4-channel Low-side Injectors INJ[1:4];



2-channel Low-side O2 Heaters O2H[1:2];



2-channel Low-side Solenoids SOL[1:2];



5-channel Low-side Relays RLY[1:5];



2-channel Low-side LED[1:2].

All drivers support the same failure diagnosis.

7.1

Diagnosis

The driver has the following fault diagnosis:

Overcurrent (Short To Vbat) protection in On Phase (OVC);

Open Load in Off phase (DIAGOL);

Short to Ground in Off Phase (DIAGLV);

Over Temperature Protection in On phase (OT).

When an overcurrent fault is detected the driver switches off with higher slew rate (FAST

SR) to reduce the power dissipation.

7.1.1

ON state - overcurrent protection

An overcurrent protection is present for LS transistors of each driver channel. Once the

overcurrent fault is detected the faulted power MOS is switched off and a fault bit is set. This

bit can be reset by every Read Diag Communication to re-activate the power stage in this

two condition:



The MSC command still High, when the Fault OVC Bit is read by MSC communication.



The MSC command becomes Low and then again High.

To increase EMC robustness and avoid unwanted fault triggering a small deglitch filter is

applied.

In order to avoid false OVC detection during the turn on slew rate phase, an analog blanking

time filtering strategy is implemented. This means that the OVC comparator output is

masked until the driver gate voltage has reached a threshold value which guarantees that

the slew rate phase is ended.

7.1.2

ON state - thermal protection

To protect power stages from temperature overheat (high battery range of operation, soft

short conditions, etc.) a dedicated thermal sensor placed close to power MOS is present in

the layout sensing FET temperature; One threshold is implemented (T_SD_H) with

Hysteresis (T_SD_hys). When the T_SD_H threshold is detected the Driver switches OFF.

Once the power stage has been switched-off for over-temperature detection, it will be able

to switch on again when temperature is decreased below thermal shut down threshold plus

hysteresis value to avoid high frequency on-off cycling.

L9788 Datasheet(PDF) 83 Page - STMicroelectronics

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