STGAP1ASTR datasheet(38/70 Pages) STMICROELECTRONICS

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Functional description

STGAP1AS

38/70

DocID029344 Rev 2

7.14.2

GOFF to gate path check

The purpose of this security check is to verify the path integrity including the driver's GOFF

output, the GOFF (turn-off) gate resistor, the power switch gate and the CLAMP pin (see

Figure 17

To perform this test, the following procedure has to be followed:



Set SD = low



Send StartConfig command



Set GOFFCHK = '1'



Send StopConfig command



Wait tGchk + tGATE_GOFFchk



Read DESAT flag

–

DESAT = '0' → OK (VCLAMP < VCLAMPth)

–

DESAT = '1' → FAIL (VCLAMP > VCLAMPth)

During the check a small current IGOFFchk will be sourced from the CLAMP pin while GOFF

is on keeping the gate low through the turn-off gate resistor.

To ensure the check result, some applicative conditions have to be verified:

–

The bleeding resistor, sometimes present between the gate and source in the

power switch, shall be higher than 8.2 k

.

–

During the test, the power switch gate shall have the time to be charged up to

VCLAMPth by IGOFFchk. In case no bleeding resistor is present, this time can be

roughly computed as:

tGATE_GOFFchk ≈ CGATE * (VCLAMPth - VL) / IGOFFchk

If a bleeding resistor is present or an additional push-pull circuit has been added,

the time has to be computed with the adequate corrective factors.

If the check fails due to the lack of the GOFF resistor, the power switch gate will gradually

rise up to VH with no protections of SENSE nor DESAT. The user test routine shall consider

this behavior.

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