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TPS548A28EVM: TPS548A28

XIN XIE
Prodigy 60 points
Part Number: TPS548A28EVM

Hi TI team

I buied a TPS548A28EVM and tested the transients load response, The testing reslut are different with those in the 2.6 chapter of the user's guide .

My testing load is same with the guide, 2A/us, 4A to 11A.Please see my test wavefrom.

The peak value is 124mv,and the EVM value doesn't exceed 80mv.

If I increase the time scale of scope, for get more tests at scope.The peak results of each test are not exactly the same at load decrease.

Could you help me to analysis？

  • 0
    TI__Mastermind 18605 points

    I checked the un load slew rate and it seems lower than 2A/us.   1.2A/us that may explain the difference in results.

    The unload results results is greater than load step.  On the load step, to improve the response more high side fet switching occurs to improve to undershoot. 

    on the unload, the device can only stop switching the high side fet.    A feedforward capacitor across the high side feedback resistor may improve the unload response.

  • 0 in reply to David_Daniels
    Prodigy 60 points

    Hi David

    Yes, The feedforward capacitor across the high side feedback resistor can imporve the unload response, the reference ID is C18, The value is 2.2nf at the TPS548A28EVM, Currently the capacitor is not builded, I can try this experiment.

    But my one point is the peak results of each test are not exactly the same on the unload, please see my sencond wavefrom, The four red arrows are all on the unload.

    Thanks.

  • +1 in reply to XIN XIE
    TI__Mastermind 18605 points

     I think the timing of the unload step with respect to the high side and low side fet conduction is causing the difference. 

    When the high side fet is on, energy is transferred to the output.   

    If the unload step happens soon after the high side fet turn on, the overshoot will be at the peak. 

     If the unload step occurs, just before the turn off of the low side fet, the overshoot will be lower. 

    Falling edge trigger on the load,   place a scope probe on the SW node, zoom in ~ 2us/div. 

     The unload transient voltage will be greater, if the unload occurs with SW node is high and the transient should be lower if the unload occurs when sw node is low.