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TPS543620: Transient time too long

Yuting Shao
Genius 13001 points
Part Number: TPS543620

Hi team,

I have test the TPS543620 on its EVM and the test conditions are:

Vin=7.5V, fsw=1MHz, Vout=0.85V, Iout=1.4A to 2.7A(2.1A/us) or 1.4A to 0.9A(2.8A/us), Cout=22uF+15uF, Mode resister=27kOhm, resister divider is 3.6kOhm(top)&5.1kOhm(bottom).

Please refer to the below waveforms. It's obvious that the transient time is too  long, but I'm not sure what's wrong. Could you help me solve it? Many thanks!

  • 0
    TI__Mastermind 48200 points

     

    What do you mean by "the transient time is too long" ?

    Do you mean that the transition time of the load-step you are trying to create is taking too long?

    Load step-up right is now taking about 10us and step-down about 5us.

    Or do you mean that the recovery in the output voltage after a load-change is taking too long (still -40mV in the load-step after >50us) ?

  • 0 in reply to Peter James Miller
    TI__Mastermind 35115 points

    Hi Yuting,

    One question to add onto Peter's. Where are you measuring Vout and how are your applying the load transient?

    I am guessing that you are referring to the settling time in the Vout after the load step. If I am right, I wonder if the issue is the Vout is being probed relatively far from the TPS543620's FB sense point. DC drops between the TPS543620 sense point and the Vout probe point would cause the behavior you are seeing.

    Lastly I am guessing this is related to the same application I have been discussing through e-mail with Hollis Liu?

  • 0 in reply to Anthony F
    TI__Genius 13001 points

    Hi Peter, Anthony,

    Thanks  for your quick response.

    We have found the cause that there is DC drop between PGND_EFF_U1 and PGND since this trace is too narrow.

    I'm a rotator at Hollis's team and Hollis is my mentor. Many thanks for your support!

    BR,

    Robin

  • 0 in reply to Yuting Shao
    TI__Mastermind 48200 points

     

    Robin,

    Very glad we could help you find the cause of the problem so quickly.  Best of luck.