L9965P datasheet(48/104 Pages) STMICROELECTRONICS

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3.7.2.6

Pyro deployment FETs test

This step aims at verifying that HS and LS FETs can be switched ON/OFF.

This test requires HWSC (hardware self-check) prior to execution to cover possible faults determining VRCM out

of range. It also requires the VRCM check to verify that diagnostic currents are in range. To achieve safety

targets, it is strongly recommended to apply such a strategy before running this test.

Figure 23. HS/LS deployment FETs test

HS PMOS

LS NMOS

VVRCM_REF

o_pf_pr_sel

RPYRO

PGND

CESD

The diagnostic works as follows:

•

PF (HS) switch test:

–

The VRCM is connected to PF pin.

–

The HS FET is turned ON.

–

The VRCM sinks current trying to maintain VVRCM_REF.

–

If the FET is working properly, this current exceeds the threshold ILEAK_SINK_TH for the filter time

tFET_TEST_FLT, the PF_FET_STB flag is set and the HS FET is turned off immediately.

•

PR (LS) switch test:

–

The VRCM is connected to PR pin.

–

The LS FET is turned ON.

–

The VRCM sources current trying to maintain VVRCM_REF.

–

If the FET is working properly, this current exceeds the threshold ILEAK_SOURCE_TH for the filter time

tFET_TEST_FLT, the PR_FET_STG flag is set and the LS FET is turned off immediately.

The FETs test diagnostic step duration is tFET_TEST.

In both tests the current on PF and PR pins will not exceed the VRCM current limits IVRCM_SOURCE_LIM or

IVRCM_SINK_LIM. During FETs test, energy available to the load is limited to less than EFET_TEST.

L9965P

Functional description

DS14702 - Rev 4

page 48/104

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