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TPS2553: TPS2553 question of ripple current of the output capacitor?

Bob Lee62837
Mastermind 7230 points
Part Number: TPS2553

Dear support member,

My customer used TPS2553.

I have a question.

Question
When selecting the output capacitor
How decide ripple current of the output capacitor?

Is ripple current of the output capacitor more than current limit value of TPS2553?


Capacitor is 220uF electrolytic capacitor.

Best regard.
Bob Lee.

  • 0
    TI__Expert 8980 points

    Hi,

    Cap ripple is influenced by load transient or Vin transient .  You can use I=C*du/dt to calculate it.

    Regards,

    Bao

  • 0 in reply to Bob Ma
    Mastermind 7230 points

    Dear Bao,

    Thank you very much for reply.

    May I have add a question?

    Question
    If Cap ripple is less than load transient or Vin transient design value,
    Is there problem?


    Best regard.
    Bob Lee.

  • 0 in reply to Bob Lee62837
    TI__Expert 8980 points
    Hi, Bob，

    For transient ripple it’s okay. But if tps2553 vin is a DC-DC, you need to optimize the DC-DC ripple, otherwise fault deglitch time will be influenced.

    This week is CN holiday. If any further questions, can I reply you when I go back to office next Tuesday?

    Regards,
    Bao
  • 0 in reply to Bob Ma
    Mastermind 7230 points

    Dear Bao,

    Thank you very much for reply.
    May I ask add a question?


    Question1
    VIN rises to 5V at 2ms with soft start with DCDC.

    Since TPS2553 uses output capacitor is 220 μF,
    The ripple current from the formula is
    I = C * du / dt

    C: 220uF
    dv: 5 V
    dt: 2 ms

    I = 220 × 10 ^ - 6 × 5 /2 × 10 -3
      = 0.55 A


    Does Cap ripple current need more than this 0.55A?


    Question2
    If Cap ripple is less than design value,
    How will it affect deglitch time?
    Will it be shortened?
    Will it be long?

    Could you reply me when you go back to office after next Tuesday?

    Best regard.
    Bob Lee.

  • 0 in reply to Bob Lee62837
    TI__Expert 8980 points

    Hi, Bob,

    Are you try to define output cap for TPS2553 application? See my input below for your question:

    1. Actually, the current you calculated is injected more in input cap of TPS2553 and output cap of DC-DC, the ripple for this is the current * ESR. To use TPS2553, you don't need to consider the ripple at soft start. You just need to optimize DC-DC operating ripple(switching ripple and output cap charge and discharge ripple). If there's low frequency ripple in TPS2553 Vin from 20kHz to 270kHz, fault deglitch time will be prolong.

    2. For ripple, it will not influence deglitch time. Below is TI suggestion for input and output cap.

    Feel free to ask any questions.

    Regards,
    Bao

    --------------------------------------------------------------------------------------------------------------------------------------

    Please verify the answer by clicking the green  "RESOLVED MY ISSUE " button in case the reply solved your question.

  • 0 in reply to Bob Ma
    Mastermind 7230 points

    Dear Bao,

    Thank you very much for reply.


    When I select output capacitor,
    I want to decide ripple current of the output capacitor.

    I ask question about ripple voltage is not,
    but question is about ripple current of output capacitor.


    May I ask a question about deglitch time?


    Your answer of Oct 5th
    "But if tps2553 vin is a DC-DC, you need to optimize the DC-DC ripple, otherwise fault deglitch time will be influenced".

    Your answer of Oct 9th
    "For ripple, it will not influence deglitch time".


    Which is correct?

    Best regard.
    Bob Lee.

  • 0 in reply to Bob Lee62837
    TI__Expert 8980 points
    Hi, Bob,

    Sorry for confusion.

    Vin ripple will influence the deglitch time, but vout ripple will not influence the deglitch time. You do need to optimize the DC-DC ripple(for Vin of TPS2553) incase influence deglitch time.

    Regards,
    Bao
  • 0 in reply to Bob Ma
    Mastermind 7230 points

    Dear Bao,


    Thank you very much for reply.

    Best regard.
    Bob Lee.