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L9679P 数据表(PDF) 164 Page - STMicroelectronics |
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L9679P 数据表(HTML) 164 Page - STMicroelectronics |
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164 / 272 page  Deployment drivers L9679P 164/272 DocID029275 Rev 1 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. The condition of two open channels, i.e. without squib resistance connecting SFx to SRx, that have a short between loops on SFx cannot be detected. If only one of the two shorted SFx pins is open, the fault will be indicated on the open channel. Squib resistance measurement During a resistance measurement, a two-step process is performed. At the first step, both ISRC current generator and ISNK current limited switch are enabled and connected to the selected SFx and SRx channel, through ISRC, ISRC_CURR_SEL, ISNK and RES_MEAS_CHSEL bit fields in the Loop Diagnostic Request Register (LPDIAGREQ). The ISRC current can be configured to either 40 mA or 8 mA nominal value through the ISRC_CURR_SEL bit in the LPDIAGREQ register providing the user with two different measurement range options. A differential voltage is created between the SFx and SRx pin based on the ISRC current and squib resistance between the pins. The SPI interface will provide the first resistance measurement voltage (Vdiff1) based on the amplifying factor of the differential amplifier and a 10 bit internal ADC conversion. The second measurement step (bypass measurement) is performed redirecting ISRC to the selected SRx pin, while keeping ISNK on; this way, the differential amplifier and following ADC will output the offset measurement through SPI (Vdiff2). Microcontroller is then allowed to calculate the mathematical difference between first and second measurements to obtain the real squib resistance value. Vdiff1 GRSQ ISRC_* RLKG_SF RSQ RLKG_SF RSQ + -------------------------------------------- RSQ RLKG_SF RSQ + -------------------------------------------- VLKG_SF VSRx_RM – + + = + GRSQ Voff_RSQ Vdiff2 GRSQ RSQ RLKG_SF RSQ + -------------------------------------------- VLKG_SF VSRx_RM – GRSQ Voff_RSQ + = RSQ Vdiff1 Vdiff2 – GRSQ ISRC_* ----------------------------------------- = (assuming RLKG_SF >> RSQ) Table 10. Short between loops diagnostics decoding Fault condition on squib channel Channel leakage diagnostics with PD_CURR on (for other channels than the one under test Channel leakage diagnostics with PD_CURR off (for all channels) No shorts No fault No fault Short to battery STB fault STB fault Short to ground STG fault STG fault Short between loops STG fault No fault |
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