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TPS65130EVM-063: Improving ripple performance on TPS65130EVM

Jason Haedt
Expert 4600 points

Part Number: TPS65130EVM-063

Hello,

I have used the TPS65130 to create a +/- 5.5V rail from a 5V input.  I was curious about improving the ripple on the negative output. 

I am attaching my two scope shots. 

TEK00003 is the negative rail measured across the output caps (This ripple is 90mV, would like to get to 45mV)

TEK00004 is the positive rail measured across the output caps (This ripple is within specification)

 

I took the stock EVM and swapped out R3 = 576k and R5 = 750k.  I did not modify anything else.

 

Do you have suggestions on improving this?

 Thanks,

Jason Haedt

TEK00003

TEK000004

  • 0
    TI__Expert 8010 points

    Hello Jason,

    First I'd like you to refer to the attached document to get clear about the naming convention.

    Because it looks like you are referring more to the switching noise than to the actual output voltage ripple of the inverting buck-boost stage.

    How did you measure the output voltage ripple (barrel or alligator clip)?

    Besides from that the 'ripple' of the boost converter looks quite strange to me, as the frequency does not match. The frequency of the output voltage ripple should be the switching frequency (1.2MHz).

    Could you describe the measurement setup for this ?

    • How does VIN look like (any oscillation superimposed on it?)
    • Did you apply a load ? If yes, resistive or electronic load?

    Thank you.

    Best Regards.

    IlonaTI_Output Voltage Ripple_Definition_ProbeTechniques_072717.pdf

  • 0 in reply to Ilona
    TI__Expert 8010 points
    Hello Jason,

    Do you have any feedback on this? Have you managed to improve the performance?

    Best Regards.
    Ilona
  • 0 in reply to Ilona
    TI__Expert 4600 points

    Ilona,

    I did change the device to fixed PWM mode and this cleaned up the positive and negative supply.  I will have to look at optimizations on the negative rail and was curious if there are any generic comments on cleaning up noise before an LDO with the inverting buck boost stage.  

    -Jason 

  • 0 in reply to Jason Haedt
    TI__Guru 65340 points
    Hello Jason,

    It depends on which type of noise you want to clean up. If you want to remove the high frequency noise coming from the switch node, a high-frequency capacitor connected directly from the output node close to the diode to PGND of the IC could help (place it as close as possible to the IC with minimum trace length).
    If you are speaking about output ripple, this is normally reduced with increase output capacitance. To keep the IC stable it helps to reduce L if you increase C.

    Best regards,
    Brigitte