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TPS546C20A: SMB_ALRT pulled low on start-up

Kai Wei Hoo
Prodigy 65 points
Part Number: TPS546C20A

We have a design which has SM/PMBus pulled-up later than the power sequence of TPS546C20A through CNTL pin.

  • This results in “oth” flagged in STATUS_CML (7Eh) register, subsequently pulling-down SMB_ALRT.
  • By sending command CLEAR_FAULTS (03h), SMB_ALRT is cleared.
  • This has been tested on TPS546C20AEVM1-746 evaluation module:
  1. Pull up SMBus DATA and CLK​
  2. Power up device​
  3. SMB_ALRT pulled-up by TPS546C20A.BP3​
  4. SMB_ALRT is high (inactive)​
  1. Power up device​
  2. SMB_ALRT pulled-up by TPS546C20A.BP3​
  3. SMB_ALRT pulled low (active)​
  4. Pull up SMBus DATA and CLK​
  1. Send command CLEAR_FAULTS (03h).
  2. SMB_ALRT is cleared to high (inactive).
  3. STATUS_WORD (79h) and STATUS_CML (7Eh) are reset.
  4. Power supply output is uninterrupted.

 

 

Is this an expected behaviour, and will SMB_ALRT being pulled low affect power supply output?

If PMBus is not implemented and TPS546C20A operates fully pin-strapped, is there any adverse effect if DATA, CLK and ALERT remains connected to the SMBus? 

  • 0
    TI__Genius 11315 points

    Hey Kai,

    TPS546C20A expects SMBus to be pulled-up before it is powered up, “oth” will be flagged in STATUS_CML (7Eh) register upon power-on, subsequently pulling-down SMB_ALRT. There is no effect of having the data and clk lines connected. If alert is still connected, then any alert on the device may be picked up with by your controller.

    Thanks,
    Caleb

  • 0 in reply to Caleb Perez
    Prodigy 65 points

    Hi Caleb, thank you for the response. 

    PMBus is not implemented, and there is no command to clear “oth” in STATUS_CML (7Eh) register, therefore SMB_ALRT is constantly pulled low during operation. In this state, will the functionality or performance of TPS546C20A as a power supply be affected by "oth” in STATUS_CML (7Eh) register and the active-low SMB_ALRT? 

  • +1 in reply to Kai Wei Hoo
    TI__Genius 11315 points

    Hey Kai,

    There is no fault response for the STATUS_CML register. The device will operate normally.

    Thanks,
    Caleb