L9788 datasheet(58/264 Pages) STMICROELECTRONICS

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Main relay driver (low-side driver)

L9788

58/264

DS12308 Rev 4

5.1.1

Overcurrent protection

When overcurrent fault is detected the Main Relay Driver MRD is switched off.

The MRD is automatically restarted every T_res if KEY_IN is still active in not permanent

battery supply scheme. No restart is done in permanent battery supply schemes.

In non permanent supply system waked up by WK_IN or WAKE_UP_EOT or

WAKE_UP_CAN, MRD OVC retry is just done before VB_IN present. No restart of MRD

after VB_IN power loss due to OVC, unless a next rising edge at WK_IN or WAKE_UP_EOT

or WAKE_UP_CAN.

The retry is done for MRD_EN_TIMEOUT from the detection of WK_IN or WAKE_UP_EOT

or WAKE_UP_CAN.

In permanent battery supply scheme in case of power up from WK_IN or

WAKE_UP_TIMER or WAKE_UP_CAN the MRD is not switched on at power up. In case of

permanent battery supply scheme and OVC protection is activated the driver is restarted by

a positive transition on the MSC MRD_ON command. It is not restarted by MSC reading.

5.1.2

Thermal protection

The overtemperature fault is detected only when VB_IN is present and the logic is out of

power on reset, so when the device is in ON state.

When overtemperature fault is detected the Main Relay Driver is switched off. In not

permanent battery supply schemes the switching off of the Main Relay Driver produces a

power down. If KEY is still active, a new power up sequence is started. If wake up from

WK_IN or EOT or CAN, or PHOLD_EN =1, no power up sequence is started. In permanent

battery supply schemes the switching off of the Main Relay Driver does not produce a power

down. The MRD is switched on again when temperature decreases to T_SD_LOW.

PHOLD_EN =1

KEY_DET/WAKE_IN_

DET/

WAKE_EOT_DET/

WAKE_CAN_DET = 0

Permanent Supply

Keep

the

status

restart by MSC

scenario 20 (see

Figure 110)

Auto restart without

limit of number

scenario 29 (see

Figure 112)

Non

Permanent

Supply

Before

Power up

N/A

N/A N/A

N/A

After

Power up

Keep

the

status

No restart

scenario 16 (see

Figure 105)

No restart

scenario 30 (see

Figure 116)

Table 25. ON state diagnostic (continued)

MRD

MSC

command

OVC

OVT

ON OFF

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