L9680 datasheet(169/286 Pages) STMICROELECTRONICS

169 / 286 page

DS11615 Rev 7

169/286

L9680

Deployment drivers

285

Figure 34. 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.

8.5.1

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

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

SSxy

SFx

SRx

SGx

22nF

1nF

22nF

Ilimit =70mA

8/40 mA

Gain = 5.25

Voffset

A to D

10bit

Tot err = ±4LSB

LSB = 2.5/1024 V

HV analog MUX

Vref =2v5

Short to GND

Rleak >10K

no detection

Rleak <1K

detection

Short to BAT

Rleak >10K

no detection

Rleak <1K

detection

Squib resistor LOW

Squib resistor HIGH

VRCM (voltage regulator current monitor)

Squib resistance measure

(system error < 8%)

Rsquib

1 to 10

Vout

Vgnd or

VBat

RLeak

EMI low pass

filter

Squib loop

driver and

diagnostic

blocks

3v3 supply

SYNCBOOST

ISRC

VER pin

(from Energy Reserve )

Safing

transistor

SATBUCK

Vgnd or

VBat

Bypass

ISINK

Ipulldown

I=1mA

GNDA

ISRC_CURR_SEL

GAPGPS02280

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