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TPS659037: SMPS7_FDBK status if not used

Ryo Akashi
Genius 9470 points
Part Number: TPS659037

Hello experts,

I have question about SMPS7_FDBK pin connection if not used.
It is described as  "Floating", is it correct?
Other _FDBK pin (e.g. SMPS6_FDBK, SMPS8_FDBK) is "Ground". I wonder why SMPS7_FDBK is not "Ground".
I would appreciate if you would give me comment.


Thanks and best regards,
Ryo Akashi

  • 0
    TI__Expert 6700 points

    Ryo,

    SMPS3 and 7 are the only two rails in the device which can be the third phase of triple phase configurations (one could combine SMPS3 with SMPS1 & 2 and SMPS 7 with SMPS 4 & 5). That is why they are spec'd differently. However, there is no issue grounding these rails if they are unused.

    Regards,

    Alex

  • 0 in reply to Alex Saenz
    TI__Genius 9470 points

    Hello Alex-san,

    Thank you for your reply.
    I understand SMPS3 and 7 can be floating if not used.

    Alex Saenz said:
    However, there is no issue grounding these rails if they are unused.

    You mentioned connecting GND is no issue, but floating is recommended?
    If grounding is also no problem, datasheet may describe "Floating or GND". But there is only "Floating", so I thought floating is better than GND.
    I would appreciate if you would give me comment which is better.
    If there is no difference, please let me know.

    Thanks and best regards,
    Ryo Akashi 

  • 0 in reply to Ryo Akashi
    TI__Expert 6700 points

    Ryo,

    Floating the SMPS3 and 7 feedback pins is better than grounding them.

    Regards,

    Alex

  • 0 in reply to Alex Saenz
    TI__Genius 9470 points

    Hello Alex-san,

    I'm sorry for my late reply.
    I checked Design checklist excel file and SMPS7 feedback pin connection (if not used) is described as in below
    Floating (if in triple-phase), GND if unused.



    I'm confused which is better.
    Could you tell me which is better and the reason of the selection (floating or GND)?
    I would appreciate if you would give me reply.

    Thanks and best regards,
    Ryo Akashi

  • 0 in reply to Ryo Akashi
    TI__Expert 6700 points

    Ryo,

    Could you give me the full part number on the top side marking? That way I can look and see if this is a triple phase configuration (which would require you to leave it floating), or if it is not triple-phase then tying the pin to GND would be preferred.

    Regards,

    Alex

  • 0 in reply to Alex Saenz
    TI__Genius 9470 points

    Hello Alex-san,

    Full part number is TPS6590378ZWS.
    From user guide, it seems to be dual-phase. If we follow excel schematic check list, GND seems to be better.
    From your comment and datasheet, Floating seems to be better.

    Let me ask some questions.
    Q1.
    For TPS6590378ZWS, GND is better when SMPS7 pin is not used.
    Is it correct?

    Q2.
    Could you tell me why Floating is better for triple-phase?
    Also, could you tell me why GND is better for not triple-phase?

    I'm confused the detail and I would like to clarify the difference.
    I would appreciate if you would give me advice.

    Thanks and best regards,
    Ryo Akashi

  • 0 in reply to Ryo Akashi
    TI__Expert 6700 points

    Ryo,

    I will need to check with my designer as to the exact functionality differences when it is in tripple-phase. I will get back with you tomorrow.

    Regards,

    Alex

  • 0 in reply to Alex Saenz
    TI__Genius 9470 points

    Hello Alex-san,

    Thank you for your support. I'm sorry, let me clarify my question.
    We want to know recommended pin status ("Floating" or "connecting GND") for SMPS7_FDBK pin when it is not used.
    I would appreciate if you would give me comment recommended pin status and the reason.

    Thanks and best regards,
    Ryo Akashi

  • 0 in reply to Ryo Akashi
    TI__Expert 6700 points

    Hi Ryo,

    apologies for today as my designer was out of the office. He should return tomorrow and I can hopefully get you a more detailed explanation.

    Regards,

    Alex

  • 0 in reply to Alex Saenz
    TI__Expert 6700 points

    Ryo,

    If the pin is not used, then floating the pin or grounding the pin is acceptable. If the device is in triple-phase we do not want this pin to be forced to GND as the device will need to bias it at some point. If, however, it is know that SMPS457 will never be used in triple-phase during any part of the device's lifetime, it is OK to force it to GND. That being said, even if the pin is left floating and SMPS457 is never used in triple-phase, there is no danger to the device as this is also a perfectly acceptable configuration.

    Please let me know if you need any more details. Thank you.

    Regards,

    Alex