L9678P datasheet(117/203 Pages) STMICROELECTRONICS

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L9678P, L9678P-S

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well as the pull-down current generator. If the VRCM block works properly, the short to

battery flag would be asserted.

Then, the Isink current limited switch (ISNK) is connected to SRx pin, the Voltage Regulator

Current Monitor block (VRCM) is enabled and connected to the selected SRx pin. The

Isource current generator (ISRC) is turned off, as well as the pull-down current generator. If

the VRCM block works properly, the short to ground flag would be asserted.

Figure 26. SRx pull-down enable logic

Once the VRCM block is validated, the real leakage tests can be performed. ISRC and

ISNK currents have to be kept switched off. The VRCM shall be connected to the desired

pin (either SFx or SRx pins); by doing this, also the pull-down current on the selected SRx

pin is automatically deactivated. During the test, if no leakage is present the voltage on the

selected SFx or SRx pin will be forced by the VRCM to the VREF level and no current is

detected or sourced by the VRCM. If there is leakage to ground or battery, the VRCM will

sink or source current trying to maintain VREF. Two current comparators, ISTB and ISTG,

will detect the abnormal current flow and the relative flags will be given in the LPDIAGSTAT

(these flags are not latched and report the real time status of the relevant comparators in

case of low-level leakage diagnostic test). In LPDIAGSTAT register are also reported the

channel and the pin (SFx or SRx) under test, respectively with LEAK_CHSEL and SQP bit

fields.

The pull-down currents on the other SRx pins are still active. Therefore, the leakage test

that would show a leakage to ground may be depending on a real leakage on the pin under

test or on a short between loops.

Short between loops diagnostics

In case the previous test has reported a leakage to ground fault, the short between loops

diagnostics shall be run. The same procedure is followed as described for normal leakage

tests except the fact that in this case all the pull-down current generators have to be

deactivated (not only the one for the pin under test), by means of the PD_CURR bit in the

Diagnostic Request Register (LPDIAGREQ). If a leakage or ground fault is not present, then

the channel under test has a short to another squib loop.

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