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BQ79631-Q1: BQ79631 SRN/SRP open wire diagnostic fault voltage/current

Josef Punt
Prodigy 20 points
Part Number: BQ79631-Q1


Hello,

Regarding the open wire diagnostic of the SRN/SRP channels. If I turn on the OW Sink on SRN/SRP  DIAG_COMP_CTRL3. OW_SNK[1:0] = 11, I expect the measured voltage to change in case of an open wire.
If I try this out on a open SRN/SRP connection the measured change of volatge is in the range of ~2mV. Where as the maximal clamped voltage between the pins according to the bq79631 datasheet is 0.9V. (no minimum is sepecified).


Is there any information regarding the minimal/average clamped voltage or the strength of the voltage source for open wire detection on SRN/SRP available?

Regards Josef

  • 0
    TI__Expert 6850 points

    Josef,

    The clamped voltage refers to the maximum amount of voltage that will be allowed across SRP and SRN with the VS0 and AUX0 current sources active to prevent damage to the CS ADC. 

    The SRN/P pins are not referenced in the section about open wire detection and the device cannot do open wire detection for SRN/P pins using the method described there. 

    Regards,

    Ben

  • 0 in reply to Benjamin Luty
    Prodigy 20 points

    Hello Ben, thanks for the quick answer.

    That raises for me the question whats the intended usecase behind the "Safety Mechanism SM114: CS Open Wire Detection Reference" as stated in the functional safety manual?
    and what functionality does the register DIAG_COMP_CTRL3. OW_SNK[1:0] = 11 exactly have?

    Are there besides the datasheet and the functional safety manual additional documents describing the chips behavior?

    Regards Josef

  • 0 in reply to Josef Punt
    TI__Expert 6850 points

    Josef,

    After further review, I was mistaken. DIAG_COMP_CTRL3[OW_SINK] = 0b11 does turn on a current sink that can be used to perform open wire detection for the SRN/P. Unlike VS or AUX however, SRN/P does not have a built in open wire check and all the steps must be performed by the MCU. It appears you have already taken these steps and it seems like your typical change in voltage is ~2 mV.

    Regards,

    Ben