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TDA4AL-Q1: Recommended POK threshold

Xingyu Zhu
Expert 4285 points
Part Number: TDA4AL-Q1

Dear expert,

Our customer is designing the POK module. They would like to know do we have recommended POK OV/UV threshold? Or can we share some principles that they can follow to set the trim value?

I have checked some threads, but I am still not very clear about how to set the values. We should follow the default value or need to set based on some principles?

https://e2e.ti.com/support/processors-group/processors/f/processors-forum/942706/tda4vm-power-ok-pok-modules

https://e2e.ti.com/e2eprivate/uaes/uaes-ep/f/uaes-jacinto-forum/1217366/tda4vm-q1-tda4vm-pok-threshold-set/4666150?tisearch=e2e-sitesearch&keymatch=pok%20threshold#4666150

Best Regards,

Xingyu Zhu

  • 0
    TI__Expert 4285 points

    Hi expert,

    Adding a more question, in TRM, IPOK_VMON_CAP_VDDS is used for monitoring CAP_VDDS0_MCU that is an internal LDO output, and we don't know the reasonable voltage range. Could you please also help to give a recommended POK threshold for this module? Thanks.

    And we find the CAP_VDDS is not included in the safety manual. Does it mean it is not required for FuSa?

  • 0 in reply to Xingyu Zhu
    TI__Mastermind 19980 points

    Xingyu,

    the POKs circuits are setup to monitor the average voltage of a domain. As such, they will not catch a single instantaneous dip in the voltage; a bad POK value indicates something is wrong while a good POK value does NOT indicate that nothing is wrong.

    Given the behavior of the POKs, I would tend to treat them as sanity checks, and because of that, I would leave margin in the thresholds.

    For the CAP_VDDS, I think you will find that for 1.8V I/O rails, the CAP_VDDS voltage will be 1.8V; for 3.3V I/O rails, the CAP_VDDS voltage will be 3.3V / 2.

  • 0 in reply to Kevin Lavery
    TI__Expert 4285 points

    Hi Kevin,

    Thanks for your reply. Below is the feedback from customer. Could you please help to share some comments?

    Kevin Lavery said:
    Given the behavior of the POKs, I would tend to treat them as sanity checks, and because of that, I would leave margin in the thresholds.

    So our recommendation is to set the threshold a little larger than 5%, such as 10%. Customer would like to know if the voltage difference is between 5-10%, POK will not be able to report the fault. Is it reasonable? Customer's understanding is that if the voltage is out of spec, POK can detect them and then to protect SoC.

    Kevin Lavery said:
    For the CAP_VDDS, I think you will find that for 1.8V I/O rails, the CAP_VDDS voltage will be 1.8V; for 3.3V I/O rails, the CAP_VDDS voltage will be 3.3V / 2.

    Understood the normal voltage level of CAP_VDDS. Customer wants to confirm that:

    1. Given that this is not included in the safety manual, for functional safety purpose, do they need to use this POK module? 

    2. If they need to use that, how to set the POK threshold? Customer don't know the reasonable voltage range of CAP_VDDS?

  • 0 in reply to Xingyu Zhu
    TI__Mastermind 19980 points

    Xingyu,

    The POK measures the voltage at n time slots (defined by DEGLITCH_SEL). The voltage must be out of range for all time slots before the POK is delared BAD. The POK is NOT an instantaneous monitor but instead is looking at the long term behavior of the rails. 

    The +/-5% quoted from the data manual really is an instantaneous voltage requirement.

    The customer is expert on how they use this block in their safety concept. They can set the voltage threshold as they see fit with due precautions for false failures.

    Kevin