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design method of TPS82085

Pokkun
Genius 4695 points
Other Parts Discussed in Thread: TPS82085

Hello.

My customer is currently in using TPS82085,now.

I have gotten a question about this product .

So, please teach me about TPS82085.

＜Question＞

My customer uses TPS82085 in 8 unit/set.

They have the wrong behavior in that circuits.

Could you tell me the problems in the circuit diagram or pattern diagram ?

( Circuit diagram and pattern diagram also will send )

Please tell me advice！

Phenomenon A

＜Circuit＞

＜Waveform＞

＜Ｐattern Layout＞

Phenomenon B

＜Circuit＞

This phenomenon is sometimes a successful boot.

（" Waveform2 " reference）

＜Waveform1＞

＜Waveform2＞

 

＜Ｐattern Layout＞

Could you help us?

Best Regards,

Pokkun

  • 0
    Genius 4695 points
    ＜Additional comment＞
    ・There is a system of "5V⇒3.3V,2.5V,1.5V",so that have occurred in the lineage of only 3.3V.
    ・That behavior isn't changes without input line L(260H).

    〇Customer opinion〇
    For phenomenon B, we believe that whether the inrush current is not the cause.
    The reasons, but one in three is for oscillation did not occur, this board has become so as to be connected to the small board.
  • 0 in reply to Pokkun
    TI__Guru*** 142860 points
    Your question is not completely clear. It seems that Vout comes up before EN on the fist waveform? Should the yellow trace be PG instead?

    The second and third waveforms look very much like the hiccup current limit in the device. I explain this here: www.ti.com/.../slyt669.pdf

    What is the load and total output capacitance present on these rails?
  • 0 in reply to Chris Glaser
    Genius 4695 points

    Sorry, that reply is too late.
    (This project has a long development period , so there was no response from the customer. )

    Thank you for document.

    ＜Additional question＞
    Is there a simple approach that Identify that it is the "Hiccup Current Limit in the device"?
    　( Without additional external soft-start circuit in this document )
    　Because….
    　My customer is currently in Trial production.
    　So can't add an external circuit .

    Please tell me.

    Sekiguchi

  • 0 in reply to Pokkun
    TI__Guru*** 142860 points
    Before we try and fix something, let's confirm the behavior we are looking at. Please confirm the trace labels on the waveforms, and report the load and total Cout being used. As well, a waveform of Vin, Vout, EN, and L would help.

    You can tell if it is hiccup by seeing if there are 32 pulses on L at a time, followed by an off time. This operation is explained in the D/S.