L9780 datasheet(27/56 Pages) STMICROELECTRONICS

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L9780

Diagnostic

If INRC pin is below the corresponding voltage threshold reported in Table 13, a possible

short to ground condition is detected. Possible short to ground condition is confirmed by the

logic (and reported in the SPI output register) only if the duration of the fault is greater than

a filter time, defined as a multiple of the clock period; in other words, when the possible

sensor short to ground condition is detected, a logic counter starts and when the count

reaches the value defined inTable 17, the fault condition is considered validated. This

counter is reset when the possible short to ground fault is cleared and after every power on

reset.

Actions

Once the INRC short to ground fault is validated (the duration of possible fault is greater

than the filter time) the following action is taken:

Set the STGRC bit in the SPI output register.

This action remains valid until cleared by the user.

5.3

SNS pin short to ground

The device is able to detect and take actions when a short to ground condition happens on

SNS pin.

If SNS pin is in the range SNS_NTH < SNS < SNS_PTH (SNS_NTH, SNS_PTH thresholds

values reported in Table 13), a possible short to ground condition is detected. Possible short

to ground condition is confirmed by the logic (and reported in the SPI output register) only if

the duration of the fault is greater than a filter time, defined as a multiple of the clock period;

in other words, when the possible sensor short to ground condition is detected a logic

counter starts and when the count reaches the value defined in Table 17, the fault condition

is considered validated. This counter is reset when the possible short to ground fault is

cleared and after every power on reset.

Actions

Once the SNS short to ground fault is validated (the duration of possible fault is greater than

the filter time) the following action is taken:

Set the STGSNS bit in the SPI output register.

This action remains valid until cleared by the user.

Application note

When the regulation loop is approaching the condition

 =1, that in terms of electrical

parameters means to have 450 mV as output of the reference cell (applied on INRC pin), the

output current of the VCCS is very small so the voltage of SNS is near to GND. This does not

flag a fault condition but the STGSNS bit in the SPI output register is expected to be set.

5.4

Heater diagnostic

The device is able to detect and take actions when a fault condition happens on external

heater FET, connected to the device through HG and HD pins. Detected fault conditions are:

heater short to battery, heater short to ground, heater open circuit.

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