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TPS54331: TPS54331DR 1.2V Vout overshoot problem !!!

Cheney_Sun
Intellectual 595 points
Part Number: TPS54331

Hi TI EE:

    Tps54331DR 5V to 1.2V buck circuit as bellow and the load current is about 200mA,and this1.2V is for DSP&FPGA.

The test Waves are as bellow two figures:

C1:5V Vin   C2:Vsense of TPS54331DR Pin5    C3:D1 VR      C4:1.2V Vout

When Vsense is above 800mV,the TPS54331DR Still have pwm,that make 1.2V overshoot as high as 1.368V

The bellow fig shows that,Tps54331 first duty is 7.3us,after the first duty,Vout is 1.314V and Vsense is 868mV.But after the first duty,although Vsense is 868mV and the TPS54331DR still have 4 pwm ,that make the 1.2V overshoot even more serious.

Please help to explain the phenomenon and solve the overshoot problem ASAP.Tks!

Best Regards

 Cheney_Sun

  • 0
    TI__Genius 10070 points
    Hi Cheney,

    You should see the comp pin waveform, the FB voltage can't reflect the PWM directly.
    The picture is not clear, could you please provide a clear waveform? From the waveform, it seems the input voltage is not constant, what is the condition?

    Shawn
  • 0 in reply to Shawn Nie
    Intellectual 595 points

    Hi Shawn:

                   Thank you for your help.The overshoot occurs during 5V Input power on and off.

    Updated figures as bellow

    C1:5V Input C2:Vsense C3:D1 VR C4：1.2V Vout

    The Comp Pin6 Waveforms as bellow figures

    C1:5V Input C2:Comp PIN6 C3:D1 VR C4:1.2V Vout

    Thank you!

    Best Regards

    Cheney_Sun

  • 0 in reply to Cheney_Sun
    TI__Genius 10070 points
    Hi Cheney

    Please test the start-up waveform, let the power supply increase from 0 to 5V. From the waveform, the input voltage changes too frequently, and it will trigger the UVLO.

    In addition, you can change Rcomp to 100Kohm to increase the bandwidth.

    Shawn
  • 0 in reply to Shawn Nie
    Intellectual 595 points

    Hi Shawn:

                     Thank you for reply.

                     When 5V power off ,from 5V to 0V ,1.2V still have the overshoot problem.Input 5V  fall down to 0V changes very frequently too.

                     When TPS54331DR Vin is around 3.5V and it will trigger the UVLO? 

                     I will change Rcomp to test tomorrow and then feedback the wavefroms.

    Best Regards

    Cheney_Sun