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TPS7A7001: FB Register

T Kishi
Genius 4425 points
Part Number: TPS7A7001

Hi

My Customer has question.Please cooperate me.

It has already been mass-produced, so Please I want you to respond quickly.

As a result of revising the data sheet, the recommended range of FB R2 resistor has been changed from [10 kΩ to 50 kΩ] to [22 kΩ to 33 kΩ].

Customers have already mass-produced with R2 = 22 kΩ, and are concerned about the effect of exceeding this recommended range.

I saw this article.

e2e.ti.com/.../626597

However, from this article I think that there is a possibility of a problem

when the resistance value is large, why did the recommended resistance value narrowed down?

Also,Does it affect the inner loop characteristics?

Beset Regard

T Kishi

  • 0
    TI__Mastermind 23361 points
    Hi T Kishi,

    Usually LDO will need certain amount of load for stability and accuracy reasons. There are usually two reasons for the adjustment. First one is to get the most common value for the resistor for cost purpose. Second is to minimize the current loss from the resistors pairs by maintaining the minimum load requirement.

    I see the revision actually increase the size for the minimum required resistors and your resistor is still within this range, I am not seeing an issue here.

    Regards,
    Jason Song
  • 0 in reply to Jason Song
    Genius 4425 points
    Hi Jason

    Sorry,My description was wrong.

    In "Revision F TPS7A7001DS", it write [27 kΩ to 33 kΩ].
    Does the problem occur if it is less than the recommended resistance value?

    Best Regard
    T Kishi
  • 0 in reply to T Kishi
    TI__Mastermind 23361 points
    HI T Kishi,

    I don't think it to be a problem. But let me do some research on the reason the datasheet revised the R2 resistance range. Will get back to you early next week.

    Regards,
    Jason
  • 0 in reply to Jason Song
    Genius 4425 points

    Hi Jason

    Thank you for your response.

    However, the Customer seems to want to know the reason of the R2 range.

    I'm sorry to hurry, but would you please respond as soon as possible?

    Best Regard

    T Kishi

  • 0 in reply to T Kishi
    TI__Mastermind 23361 points
    Hi T Kishi,

    The reason for the narrow down on the feedback resistor is due to the reason that at high temp, the accuracy may get a small impact from the resistor. They narrowed it down to help with the yield. If you already have them in place, I would recommend leave them as it is.

    Regards,
    Jason Song
  • 0 in reply to Jason Song
    Genius 4425 points
    Hi Jason

    Thank you for your response.

    I understand that there is no problem with 22 kΩ.
    However, I do not know the reason why the precision deteriorates below 27 kΩ.

    Does accuracy mean worse due to temperature rise means that the bias current of the internal op amp increases?
    In that case, I think that there is no problem if it is 27 kΩ or less.
    ⇒ Is this understanding correct?
  • 0 in reply to T Kishi
    TI__Mastermind 23361 points
    HI T Kishi,

    Please refer to the other post, an answer has been posted on that post you mentioned earlier.

    "it is related with the bias current of error amplifer , the selection of R2 should making sure that the error amplifer is work in linear state.
    generally ,the error amplifer is OTA , so the R2 also be a part of the gain of open-loop and phase margin.
    please selecting the R2 follow the datasheet strictly ."

    Regards,
    Jason