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TIDA-01457: CBYT and Output Schottky diode on output

Part Number: TIDA-01457
Other Parts Discussed in Thread: TPS82130, , TIDA-01405

Hi Team,

Recently we are using TPS82130 as IBB. Their schematc is very close to below, except Cout is only 22uF.

My questions below:

  • Why there is no Cbyp between VIN and VOUT for stability of TPS82130?
  • If they did not connect Cbyp, TPS82130 does not have bypass from its VIN to its GND, what is the problem

Thanks!

-Wenhao

  • Hi Wenhao,

    Please take a look at Section 2.3.8 of the TIDA-01457 guide, which may answer your questions.

    Regards,
    Kris

  • Hi Kris,

    Great thanks for your good reply in this special period. As you can see from 2.3.8 below, we do not recommend adding a CBP for TPS82130 in IBB.

     However, from SLVA469C, we recommend adding a bypass cap in order to keep device stable.

    I am a little bit confused for this difference.

    • Do you know which i should refer to?
    • Do you know why we do not need bypass cap for TPS82130?

    Thanks!

    -Wenhao

  • Hi Wenhao,

    Let me see if I can find further background on the app note. I do not believe the Cbyp between Vin and -Vout is always required for stability. At any rate, the TIDA-01457 was tested and checked to be stable without a Cbyp capacitor, and not having this cap helps remove the need for a Schottky diode at the output.

  • Hi Kris,

    Thank you for your help in this special time. My customer has big worry for the need of Cbyt. Please help look on this. TPS82130 is a good part and i do not want it to have concerns in their application.

    -Wenhao

  • Hi Wenhao,

    I reached out to the original app note authors. After that app note was written, the team found that without Cbyp approach works well. This is shown in this newer app note.

    Furthermore, this 2nd reference design TIDA-01405 for TPS82130 in IBB configuration also shows no need for Cbpy between Vin and -Vout.

    Regarding one of your points in the initial post that the TPS82130 does not have bypass from its VIN to its GND:
    If you draw the current flow paths for IBB, the main power current flow paths are 1) in on state, current flows from input (Cin) through 'high-side' FET through inductor to gnd; then 2) in off state, current flows from -Vout (Cout) through 'low-side' FET through inductor to ground. In other words, the main power delivery current loops do not flow through module Vin to module GND (-Vout) in either state.
    In terms of the cap bypassing for the internal control circuitry which is -Vout referenced, I think you can consider Cin and Cout are in series as an effective bypass cap from Vin to -Vout (since Cin is Vin to system GND, then Cout is GND to system -Vout).

    I hope this information helps,
    Kris

  • Hi Kris,

    Thank you very much!

    -Wenhao