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BQ76PL455A: STK_FAULT_ERR condition?

Kotaro Yamashita
Intellectual 2560 points
Part Number: BQ76PL455A

Hi Team,

I would like to understand how to detect STK_FAULT_ERR by pl455a and submit error signal. 

Is there any specific condition? 

Regards,

Kotaro Yamashita

  • 0
    TI__Genius 9401 points

    Hi Kotaro,

    Thank you for your question! 

    You can find more information about how the fault interface works and this specific type of error on the bq76PL455A-Q1 datasheet (http://www.ti.com/lit/ds/symlink/bq76pl455a-q1.pdf) on sections 7.3.12.2 FAULT Signaling (page 38) and 7.3.12.3 FAULT Sensing (page 39). Also, page 88 has the description of the STK_FAULT_ERR.

    Basically, when no fault condition is present, a heartbeat pulse is sent from a device higher in the stack to the device below it and it has a typical frequency of 10KHz, indicating no fault on the device above. But, if the signal received by the lower device from the stacked device is too noisy or is running at the wrong frequency, a STK_FAULT_ERR will occur. The FAULT_N pin will signal a fault from both internal sources and from ICs above in the stack, if enabled. This can be enabled on registers FO_CTRL and COMCONFIG[FAULT_HIGH_EN]. 

    Best regards,

    Leslie

  • 0 in reply to Leslie Marquez
    TI__Intellectual 2560 points

    Hi Leslie,

    Could you give me more specific information about;

     > if the signal received by the lower device from the stacked device is too noisy or is running at the wrong frequency

    ?

    Are there any specific specs about noise and also frequency to issue the error flag?

    Regards,

    Kotaro Yamashita

  • 0 in reply to Kotaro Yamashita
    TI__Genius 9401 points

    Hi Kotaro,

    There is no spec for the frequency to trigger this error. There is only the specification for the heartbeat tone width (125ns) and heartbeat frequency (10KHz).

    As you deviate up or down from this 10KHz frequency, the following occurs:

    If you have an under-frequency conditions (below 10KHz), and if the FAULT interface is enabled, you will see the STATUS[STACK_FAULT_DET] and STATUS[STACK_FAULT] flags set, indicating that a fault has been detected (As a reminder, a FAULT is detected on FAULTH+-, if enabled, when there is no heartbeat tone. So, if the tone is below the expected 10KHz frequency, this will be detected as a fault).

    If you have an over-frequency conditions (above 10KHz), and if the FAULT interface is enabled, you will see the FAULT_COM[STK_FAULT_ERR] flag set, indicating that the pulse received is too noisy.

    To test the STK_FAULT_ERR, you could use lab equipment to replicate a heartbeat on the FAULTH+- lines, confirm that there is no fault detected by reading the STATUS register, and then start sweeping the frequency of the signal to frequencies higher than 10KHz until FAULT_COM[STK_FAULT_ERR] trips. 

    Best regards,

    Leslie

  • 0 in reply to Leslie Marquez
    TI__Intellectual 2560 points

    Hi Leslie,

    Thanks. Let me ask more detail of this.

    For actual use case, Can STATUS[STACK_FAULT_DET] and STATUS[STACK_FAULT] detect disconnection either Fault + or -, or both? Is there other thinkable case?

    How's STK_FAULT_ERR? It's only for noise?

    Regards,

    Kotaro Yamashita

     

  • 0 in reply to Kotaro Yamashita
    TI__Genius 10785 points

    HI Yamashita,

    If FAULT +/- is disconnected then you won't have heartbeat. If cable is disconnected then you won't have proper heartbeat.

    So, it could be noise as well all other issues.

    Device is indicating that you have an issue.

    Device can't determine whether fault is due to the noise, missing connection and etc....

    Roger