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TPS735: Feedback resistor R2

Part Number: TPS735

Hello team,

My customer is investigating effect of datasheet revisions.

In the recommended operating conditions, R2 is recommended to be 110kOhm at nominal.

But in my customer's use case, the other resistor is used (e.g. 18k, 27k, 30k, 145.8k, 51k)

  1. If R2 is not 110k, could you please let me know acceptable range of R2?
  2. Why does TI recommend 110kOhm R2? Does it have any concern if resistor other than 110k is selected?

Regards,

Itoh  

  • Hello Itoh, 

    We have had a similar question over this resistor requirement in a TPS735 thread.

    Where Kyle says :

    "I cannot find a specific reason for why 110k was put in the Recommended Operating Conditions Table, my assumption is that this may have been what was used on the production test program and so he author of this datasheet put that in the table as well. I would prioritize trying to get R1||R2 = 250 kOhm to optimize for noise performance."

    Best,

    Juliette

  • Hello Juliette-san,

    I don't want to recommend my customer to change the existing design due to the thing TI doesn't know well. 

    Also, I don't think my customer will accept the unclear datasheet description.

    Could you please check it again and answer my specific questions?

    Regards,

    Itoh

  • Hi Itoh,

    I found the notes in the draft datasheet regarding the 110k resistor.  These notes were documented January 20, 2015 without any serious discussion.  However the 110k resistor value is the same as was designed into the original EVM from 2008.  Furthermore we have observed in our datasheet correction log that R2=110k typical violates the guidance later in the datasheet to set R1 // R2 = 250k.  Kyle mentioned the reasons behind 250k in his previous E2E post.

    The guidance on R2=110k is to remain consistent with the released EVM but there is no reason why the customer cannot use a different value for R2.

    Thanks,

    - Stephen