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TPS73201-EP: ESR of Cout

Hyun woo Kim1
Intellectual 430 points
Part Number: TPS73201-EP
Other Parts Discussed in Thread: TPS732

Dear TI team

TPS732 recommend to use Cout and ESR below 50nCF. I'm gonna use below Capacitor  with 10uF and  lowest ESR 3.3mohm. but it is not meet requirement below 50nCF.

but I tested in my board and there is no any rining or oscillation.

Could I have to change another capacitor ? 

  • 0
    TI__Mastermind 32795 points

    Hello Hyun,

    The design will be stable with this capacitor according to the datasheet, however there may be some ringing in the presence of a load step.  However if you have tested your design and are satisfied that you are not seeing this, then you do not need to make any changes. 

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    Intellectual 430 points

    Dear Stephen

    Thank you reply it to me, 

    I have a question. I don't understand what you said it will be stable, because  33nohmF (10uF x 3.3mohm) is not satisfied TI recommend 50nohmF. As I know the ESR value is meant lowest value all over band. right ? Please let me know it.

    Best regards,

  • 0 in reply to Hyun woo Kim1
    TI__Mastermind 32795 points

    Hi Hyun,

    The device will still be stable, however the phase margin will lower with < 50nohmF per the datasheet.  A lower phase margin does not indicate instability, it just means there will be a damped ring in the transient response.  Per the datasheet:

    The following app note may be useful to your work.  As shown in Table 1, a phase margin of 50 degrees will give 1 ring, 40.6 degrees will give 2 rings, etc.  High phase margin will give no rings.

    https://www.ti.com/lit/an/slva381b/slva381b.pdf

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    Intellectual 430 points

    Thank you Stephen

    I have a last question. 

    another LDO inquire to use specific capacitor with ESR range. but As you know, capacitor has different ESR value as frequency.

    As I know, the lowest ESR value is picked to check whether the ESR value is in recommended ESR range or not.

    Could you please confirm it is correct or not what i know about selecting ESR Value ?

    Best regards, 

  • +1 in reply to Hyun woo Kim1
    TI__Mastermind 32795 points

    Hello Hyun,

    The value of ESR at the resonant frequency of the capacitor is what you will want to use for your analysis.  For your capacitor, it is 3.3 miliohms.

    Thanks,

    - Stephen