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TPS7A7001: Output capacity specification of TPS7A7001 and TPS7A91

T Kishi
Genius 4425 points
Part Number: TPS7A7001
Other Parts Discussed in Thread: TPS7A91,

Hi

My customer has question.

TPS7A7001 has specification of maximum output capacity in data sheet, but not in TPS7A91.
What is the difference?
If there is any clear difference, I would like to have a comment.

Best Regard

T Kishi

  • 0
    TI__Guru 55940 points
    Hi T Kishi,

    Different designs require different compensation in order to achieve and maintain stability. While every LDO theoretically has a minimum and maximum capacitance, we have benched TPS7A91 with up to 1 mF of capacitance on the output while maintaining stability. As we have achieved stability with what we consider to be an extreme amount of capacitance, we do not have a real world practical maximum for output capacitance for TPS7A91.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Genius 4425 points
    Hi Ryan
    Thank you for reply.

    I want to check one,
    How do judge the achievement of stability?Bode plot?

    Regard
    T Kishi
  • 0 in reply to T Kishi
    TI__Guru 55940 points
    Hi T Kishi,

    The easiest method to judge the stability of an LDO in your application is to perform transients while monitoring the output voltage. By observing how the LDO output responds to transients and counting any ringing that may occur on the output, you will have a good understanding of how stable the LDO is in your specific application. The following application note goes into more detail:

    www.ti.com/.../slva381b.pdf

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Genius 4425 points
    Hi Ryan

    Thank you for reply.
    From this application note, is it OK to judge that the stability of TPS7A91 and others is around PM = 50 °?

    Regard
    T Kishi
  • 0 in reply to T Kishi
    TI__Guru 55940 points
    Hi T Kishi,

    Yes, if you are refering to the transient curves provided in the datasheet for TPS7A91, based on the application note, it is okay to approximate the phase marge under the transient conditions to be ~50 degrees. It is recommended that you perform transient analysis based on your application specific transient conditions in order to estimate the phase margin for your application.

    Very Respectfully,
    Ryan