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TPS54331: TPS54331 -40 Degree cold start issue

user5019564
Prodigy 30 points
Part Number: TPS54331

-40 degree cold start issue.

12V-6V/2A，VOUT is unusually step up. When the output is 6V/1A, it's OK. 

The circuit is designed and layout acoording to datasheet. Refer to datasheet FIG10, Css=10nF, L=4.7UH, R4=10K R5=470R R6=1.6K, R3=30K  C6=200PF C7=100PF, Cout=470uf

There is another TPS54331 on my PCBA, 12V-3.5V/1A, that's OK.

Could you please help me?

  • 0
    TI__Expert 4035 points

    Hi,

    Could the phenomenon be repeated on every 12V-6V/2A boards, how many boards or IC have you tried? If possible, please capture Vin and EN waveforms on the same screen.

    And also please try with lower output capacitance to see if any difference, thanks.

    BRs,

    Ryan

  • 0 in reply to Ryan Hu (BSR-MV)
    Prodigy 30 points

    Ryan,

    Thanks for your promptly reply.

    I've made four samples, every sample apply two IC, one for 3.5VA1A, another for 6V/2A. The phenomenon is consistent in 6V/2A.

    The waveform at VIN and EN is perfect a straight line. Also 68uf MLCC or 470uf solid aluminum electrolytic was tried in output, it's useless.

    Incredible,  when the loop pole capacitor--C6 200pF--was removed, the Vout climb up time is better, about 1.5s@-40deg.

    Usually the stong negative temperature coefficent of ESR will affect the loop, I do not known if there is any other factors.

    Could you please give me further guidance?

    Wish best regards

    Lubo

  • 0 in reply to user5019564
    TI__Expert 4035 points

    Hi Lubo,

    Could you please zoom in the waveform marked with red circle. Could you please provide me your schematic? thanks.

  • 0 in reply to Ryan Hu (BSR-MV)
    Prodigy 30 points

    Hi Ryan,

    Here is the zoom in waveforms and schematic. The blue is VIN, the yellow is 6Vout.

    7801.Schematic Prints.pdf

  • 0 in reply to user5019564
    TI__Expert 4035 points
    Hi Lubo,
    According to your schematic, there are too much difference to the datasheet reference design, especially the compensation network. So you have changed the parameters like to the datasheet by muanal, right? And the RECTIFIERS didoe you are using ER304, which is a 400V ABS Max voltage, so high the voltage rate..., not very resnoable for cost and efficiency.
    I suspected the OCP during the start-up, since 1A is ok while 2A is not. I try to find more useful info from the ZOOM in waveforms, but the sampling time is too large, not very clear...
    Please make sure the parameters are resonable and increasing the Css to incrase the softstart time to see any difference...
    BRs,
    Ryan