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TPS7A7001: Feedback Resistor Range

Shinichi Inoue
Guru 19671 points
Part Number: TPS7A7001

Dear Specialists,

My customer is using TPS7A7001 and datasheet was revised about R2 range.

He would like to know what kind of influences is considered in detail.

He need to know because it has already adopted current products.

I appreciate your great help in advance.

Best regards,

Shinichi

  • 0
    Guru 19671 points
    Dear Specialists,

    I forgot to attach the description of the datasheet.

    before(rev. E)
    (1) When setting VOUT to a value other than 0.5 V, connect R1 and R2 to the FB pin using 10 kΩ ≤ R2 ≤ 50 kΩ resistors. See Functional
    Block Diagram for details of R1 and R2.

    after(rev. F)
    (1) When setting VOUT to a value other than 0.5 V, connect R2 to the FB pin using 27-kΩ ≤ R2 ≤ 33-kΩ resistors. See Functional Block Diagram for details of R1 and R2

    ---question

    after revised,
    If R2 is out of range, what kind of influences are considered?
    Could you please advise in detail?

    I appreciate your great help again.

    Best regards,
    Shinichi
  • 0 in reply to Shinichi Inoue
    TI__Expert 8905 points
    Hi Shinichi,

    The datasheet was revised as using resistors outside of that range can cause the accuracy of the device to go outside of specification.

    Regards,
    David
  • 0 in reply to David Hopkins
    Guru 19671 points

    Hi David,

    Thank you for your reply.

    He has to decide whether to change resistance deppend on severity.

    He would like to know which spec has a big influence and what symjptoms occur.

    If possible, would you please teach me why the spec has changed.

    I appreciate your great help.

    Best regards,

    Shinichi

  • 0 in reply to Shinichi Inoue
    TI__Expert 8905 points
    H Shinichi,

    The output accuracy goes outside of specification at temperatures near 125C. The leakage current through the resistors effects the drift of the LDO at these temperatures.

    What size are your resistors? The resistor sizing will have a direct impact on how much out of spec the parts go.

    Regards,
    David
  • 0 in reply to David Hopkins
    Guru 19671 points
    Hi David,

    Thank you for your reply.

    I understand there is a possibility to go out of output accuracy.

    I'll confirm the customer the size of resistor and then feedback.

    I appreciate your great help.

    Best regards,
    Shinichi
  • 0 in reply to Shinichi Inoue
    Guru 19671 points

    i David,

    I could know what size of resistor the customer use.

    ---

    size:1.0mm×0.5mm

    resistor value: R2=3.6KΩ,R1=18KΩ

    ---

    Could you please tell me how much it affects the size of this resistor.

    I appreciate your great help.

    Best regards,

    Shinichi

  • 0 in reply to Shinichi Inoue
    TI__Expert 8905 points
    Hi Shinichi,

    The drift performance with those resistors should be within 5% of the nominal output voltage.

    Regards,
    David
  • 0 in reply to David Hopkins
    Guru 19671 points

    Hi David,

    Thank you for your reply.

    I'll share this information with the customer.

    If he has an additional question, I'll consult with you.

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi

  • 0 in reply to Shinichi Inoue
    Guru 19671 points

    Hi David,


    I sent your answer to the customer, they has an additional question.


    They would like to know the reason of deterioration.


    As you mentioned before, it is caused by the leakage current of resistor.


    Do You mean only resistor's problem.


    Is there a problem device side?


    I would be grateful if you could advise in detail.


    I appreciate your great help and cooperation.


    Best regards,


    Shinichi

  • 0 in reply to Shinichi Inoue
    Guru 19671 points
    Hi David,

    This is a just reminder I am still waiting for your advise.

    I appreciate your great help.

    Best regards,
    Shinichi
  • 0 in reply to Shinichi Inoue
    Prodigy 195 points
    OMG!
    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 .
  • 0 in reply to michael YANG
    Guru 19671 points
    Hi Michael,

    Thank you for your reply.

    I understand the reason of R2 value controlled.

    I'll share this information with the customer.

    I appreciate your great help and cooperation.

    Best regards,
    Shinichi