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TPS40210-Q1: VDS waveform abnormal

Walsh
Intellectual 950 points
Part Number: TPS40210-Q1

Hi,

When I used TPS40210-Q1 at low voltage input, i find that the VDS waveform is abnormal while short output start.

Topology: Flyback

Feedback: Primary side

Vin: 8~16V, (Abnormal only is happened at 8V input and 12V/14V/16V input is OK)

Test  condition: Power up after short output

Schematic:

waveform1, Q500 VDS and Vin

waveform2, Q500 VDS and VRC(pin 1)

CH1, Q500 VDS

CH2, VDD

CH3, VRC

Could you help to check the issue and give some advice.

Is the abnormal caused by RC configuration? Does it need adjust?

Thanks,

Walsh

  • 0
    TI__Mastermind 21720 points
    Hi Walsh,

    Can you please post the rest of the schematic? What is the intended output voltage? What is the intended switching frequency? IS is possible to post the conditions where the operation is correct?

    Thanks,

    Garrett
  • 0 in reply to Garrett Roecker
    Intellectual 950 points

    Hi Garrett:

    Thanks.

    Output is 12V and switching frequency is 100KHz.

    Test condition: First short output and then power up.

    Abnormal: 8Vin

    Normal: Other Vin (12V/14V/16V)

    Schematic as below

    Thanks,

    Walsh

  • 0 in reply to Walsh
    TI__Mastermind 21720 points

    Hi Walsh,

    Are you shorting the regulated rails or one of the isolated rails? 

    Also in the first provided waveform the input voltage has about 1V of ripple? Do you see this of the other conditions? Normally this should be well regulated with hardly any ripple.

    Please also try changing the RC capacitor resistor combination. Try selecting 220pF  and ~700kOhm. This might help and see if it is related to the RC pin functionality.

    Thanks,

    Garrett

  • 0 in reply to Garrett Roecker
    Prodigy 10 points

    1、I did the both side;

    2、no other conditions; i have to say the steps:a/short the output side(all of the output side i did);b/adjust the input vol equals 8V;c/turn on the converter;

    3、i changed RC, but the circuit bug still there. R 365k fixed 365k+365k. C 470pF fixed 200pF;