ADM1276 troubleshoot with the PMBUS

Hi,

Each time we read words trough PMBUS interface, the ADM1276 replies "C0". It happens with all the word registers. We monitored the SDA with an oscilloscope to confirm the "C0" word.

The powergood, the OV and UV threshold works fine.

We have already changed the components, same results.

Do you have any idea?

Thanks,

Nicolas

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  • 0
    •  Analog Employees 
    on Apr 12, 2019 7:38 PM over 1 year ago

    Hi Nicolas,

        That's a pretty wide-open question. There are many possible issues that you could be seeing. I would suggest the following:

    1) Make sure that your bus has pull-ups and that the voltage levels are appropriate

    2) Make sure that the ADM1276 is powered, as evidenced by 2.7V on VCAP

    3) Make sure you are talking to the correct address on the bus.

    4) Check your read byte or read word protocol against the datasheet, figs 55 and 57, making sure that you are using repeated start (Sr) as appropriate.

    5) Make sure that there are no address conflicts on the bus (two devices responding at the same address)

    Thanks!
      Nathan

  • Hi Nathan,

    Thanks for your reply.

    1/ We have 10k pull ups and the voltage is fine (3.3V)

    2/ We have 2.67V on Vcap

    5/ We have only one device on the bus

    3/4/ We are able to write in the ADM1276, I change the state on the N_ALERTwith the register 0xD6. We are also able to trigger the VOUT_OV_WARN_LIMIT with the good voltage written in the register x042

    I attached in the file the frame for READ Vout ( 0x8B)

    Total frame READ VinBeginingEnd

    Thanks,

    Nicolas

  • 0
    •  Analog Employees 
    on Apr 15, 2019 5:53 PM over 1 year ago in reply to nicolas_22

    Hi Nicolas,

        Unfortunately, it is very difficult for me to make out the fine details of your plots. They came across as very low resolution. Can you please confirm two things:

    1) Your bus master is using the correct Read Word Protocol, as shown in the ADM1276 datasheet, Figure 57. Please confirm that there is a Repeated Start (Sr) after the Command Code.

    2) You have sufficient hold time between clock and data.

    Thanks!
      Nathan

  • Hi Nathan,

    We found our problem, It comes from the driver which uses "1" instead of high Z.

    Thanks for your help.

    Nicolas

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