L9678P datasheet(121/215 Pages) STMICROELECTRONICS

121 / 215 page

DS11626 Rev 9

121/216

L9678P, L9678P-S

Deployment drivers

214

Figure 25. Deployment loop diagnostics

The leakage diagnostic includes short to battery, short to ground and shorts between loops.

The test is applied to each SFx and SRx pin so shorts can be detected regardless of the

resistance between the squib/pyroswitch pins.

6.5.1

Low level diagnostic approach

In this approach, each of the test steps described in the sections below requires user

intervention by issuing the proper SPI command.

High voltage leakage test for oxide isolation check

This test is mandatory to address possible leakages that could not be experienced at low

voltages on SFx or SRx pins. The Isource current generator (ISRC) is enabled on the chosen

SFx pin. To confirm that the SFx pin has then reached a suitable voltage level, a dedicated

ADC measurement on the SFx pin can be requested. Once this test is performed, a leakage

test on SFx and SRx pins can be issued to double check possible leakages.

Leakage to battery/ground diagnostics

Prior to the real test, the Voltage Regulator Current Monitor block (VRCM) has to be tested

and validated. The validation of VRCM goes into verifying both the short to battery and short

to ground flags.

The Isource current generator (ISRC) is first connected to SFx pin to raise its voltage to

VRESDIAG. Then, the Voltage Regulator Current Monitor block (VRCM) is enabled and

connected to the selected SFx pin. The Isink current limited switch (ISNK) is turned off, as

GAPGPS01129

SSxy

SFx

SRx

SGx

22nF

1nF

22nF

Ilimit =70mA

40mA

Gain = 5.25

Voffset

A to D

10bit

Tot err = ±4LSB

LSB = 2.5/1024 V

Squib resistor HIGH

Squib resistor LOW

HV analog MUX

Vref =2v5

Short to GND

Rleak >10K

Ω no detection

detection

Rleak <1K

Rleak >10K

Ω no detection

detection

Rleak <1K

Short to BAT

VRCM (voltage regulator current monitor)

Squib resistance measure

(system error < 8%)

Rsquib

1 to 10

Vout

Vgnd or

VBat

RLeak

Squib loop

driver and

diagnostic

blocks

VRESDIAG

ISRC

VER pin

(from Energy Reserve)

Safing

transistor

Vgnd or

VBat

Bypass

ISINK

Ipulldown

I=1mA

GNDA

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