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TPS40422: PMbus reading much higher than nominal voltage

Neo.Wang
Intellectual 920 points
Part Number: TPS40422

Hi TI experts,

When keep monitoring the TPS40422 output voltage (1 minute interval) through PMbus, observed high voltage spike randomly.

example for 2.5V output:

2023/07/30 19:50:29 A-TPS1-1 crossed threshold (range: 2375mV - 2625mV), current reading: 2830mV

2023/07/30 19:51:29 A-TPS1-1 reading (2494mv) is within threshold (range:2375mV - 2625mV)

We set OV threshold as 12.5% in config file.

Is this expected due to PMbus read accuracy? If not, what's the OVP mechanism of TPS40422? in case true OV happens, will this rail be turned off?

We have several TPS40422 in the same design and similar issue happened on different rails.

Please share your comments on this.

Thanks

Neo

  • 0
    TI__Mastermind 27500 points

    Hello,

    1- Is the output monitored by scope as well

    2- is there load steps during the 1 minute interval?

    Regards

  • 0 in reply to Mahmoud Harmouch
    Intellectual 920 points

    1. No, this happens in customer side in field.

    2. System is continuously running, suppose no load steps.

    3. From datasheet, when OV happens, the high side MOSFET is turned off and low side MOSFET is latched to discharge the output voltage until it within the PGOOD window. So that means the controller will not turn shut down (both MOSFET are off) the output, right?

    Thanks.

  • 0 in reply to Neo.Wang
    Intellectual 920 points

    Here are the voltage waveforms we captured.

    The 1st is for 1Vout, the 2nd is for 1.5Vout, both are generated by TPS40422.

  • 0 in reply to Neo.Wang
    TI__Mastermind 27500 points

    Hello,

    How many boards have this behavior? Can you please send schematic for review? 

    Regards

  • 0 in reply to Mahmoud Harmouch
    Intellectual 920 points

    Hi,

    FA team reported the similar issue was observed on "a few" boards.

    Here is the 1V/1.5V schematic.

    7875.TPS40422.pdf

    More logs for your reference.

    2023/09/18 11:02:07 A-TPS3-1 crossed threshold (range: 970mV - 1050mV), current reading: 869mV

    2023/09/18 11:03:07 A-TPS3-1 reading (994mv) is within threshold (range:970mV - 1050mV)

    2023/09/18 22:21:11 A-TPS3-2 crossed threshold (range: 1425mV - 1570mV), current reading: 1298mV

    2023/09/18 22:22:11 A-TPS3-2 reading (1486mv) is within threshold (range:1425mV - 1570mV)

    2023/09/19 01:41:03 A-TPS2-2 crossed threshold (range: 1425mV - 1570mV), current reading: 1292mV

    2023/09/19 01:42:03 A-TPS2-2 reading (1476mv) is within threshold (range:1425mV - 1570mV)

    2023/09/22 09:28:05 A-TPS2-2 crossed threshold (range: 1425mV - 1570mV), current reading: 1976mV

    2023/09/22 09:29:05 A-TPS2-2 reading (1478mv) is within threshold (range:1425mV - 1570mV)

    Thanks

  • 0 in reply to Neo.Wang
    TI__Mastermind 27500 points

    Hello,

    schematic looks OK. Is there any over current IOUT_OC_ FAULT reported? Can the customer measure the loop at nominal load current?

    Regards