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UCD90160A: POWER_GOOD# status bit

Daniel Carlson
Prodigy 370 points
Part Number: UCD90160A

Hello, 

I have a question from my customer regarding POWER_GOOD on the UCD90160A:

I'm looking for some details on the UCD90160A POWER_GOOD# bit found in the STATUS_WORD register. The only description I can find is from the PMBus spec.

The POWER_GOOD signal, if present, is negated [1].

Note 1: If the POWER_GOOD# bit is set, this indicates that the POWER_GOOD signal if present is signaling that the output power is not good.

 

Where is the POWER_GOOD signal on the UCD90160A. Is this a pin on the chip? Is it an internal status register. We can set the power_good on/off thesholds for each rail and use the POWER_GOOD status when building logic for the GPIOs but I don't see a paged POWER_GOOD status for each rail.

 

Furthermore the description from the PMBus spec seems to be describing the power_good# pin of a voltage regulator. This would make sense for a PMBus capable Voltage Regulator but doesn't seem to make sense for the UCD.

I'm asking because some of our boards at the factory are reporting POWER_GOOD# Status word bit is set.

Thanks,

Daniel

  • 0
    TI__Genius 9320 points

    Hi, Daniel,

    1. The POWER_GOOD# bit, if set (1b), indicates voltage on all rails are greater or equal POWER_GOOD_ON limit, set on rails. If clear (0b), indicates one or more rail(s) has voltage below POWER_GOOD_ON limit.

    2. The POWER_GOOD# signal is not a pin on the chip that you  can measure. Device monitors the voltage level on rails and update the bit accordingly.

    Regards

    Anne Ngo

    Texas Instruments

  • 0 in reply to Anne Ngo77
    Prodigy 30 points

    Hi Anne,

    Thanks for the reply. I think you have the logic reversed, a 1b should mean power is not good and a 0b should mean the power is good. Can you double check?

    The interesting thing is that we have a board where the POWER_GOOD# indicated power was bad but there was no other evidence that any of the rails were bad. There were no under/over voltage warnings or faults and no Ton_Faults on any of the rails.

    Is this POWER_GOOD# status bit latched? That is does it stay set even if the rails later get back to their normal voltage? If so then maybe there was an intermittent voltage drop that trigger POWER_GOOD# and it latched.

    So there is no way with POWER_GOOD# to pinpoint which rail has a problem is that right? As long as the rail is monitored it's status gets AND'ed together with the other rails into POWER_GOOD#, correct?

    We'll try to reproduce this problem and see if we can debug further.

  • 0 in reply to Taylor Nichols
    TI__Guru 66230 points

    Hi

    Yes, when it is set, it means at least one rail does not reach PWOER_GOOD. when it is clear, it means that all rails are POWER_GOOD.

    POWER_GOOD is not latched and it is updated real time.

    POWER_GOOD is defined by the PMBus and it is an AND result. 

    But if you open the system monitor of the Fusion GUI, you shall see the reading and status of all rails. 

    if you can not interpret, please share the snapshot of the system monitor.

    Regards

    Yihe