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TPS63060 / Capacitor in parallel with bottom resistor

S.Satoshi
Guru 21685 points

Hi,

I found following comment in datasheet then please let me ask about capacitor in pallalel with bottom resistor.

Place a small capacitor (C4, 10 pF) in parallel with R2 when using the power save mode and the adjustable version, to provide filtering and improve the efficiency at light load.

  1. Can you explain why it improves the efficiency at light load by adding C4?
  2. Do you have recommended maximum capacitance?

Best Regards,

Sonoki / Japan Disty

  • 0
    TI__Expert 7110 points
    The value of the capacitor depends on the resistor values. For a 1MOhm, we do recommend using a 10pF. What is the size of the resistors you plan to use?
    The capacitor filters noise that can be coupled in Power Safe Operation and is smoothing the feedback voltage for this case.
  • 0 in reply to Florian Feckl
    Guru 21685 points

    Hi Florian,

    Thank you for your response. My customer plan to use R1=115k and R2=10k in fig.8. Then please let me ask following three question.

    1. What capacitor value do you recommend for the case of R1=115k and R2=10k?
    2. Please let me know the reason of the limitation of the capacitor value.
    3. Please let me ask again why this capacitor will improve efficiency. Is smoothing the feedback voltage its reason?

    Best Regards,

    Sonoki

  • 0 in reply to S.Satoshi
    TI__Expert 7110 points
    It is not required to use this capacitor. It can help, however to improve efficiency for light loads. Please make sure to evaluate the solution with the chosen passives. A too big capacitor can influence the transient behavior!

    1. Please go with the recommended capacitor and check if the performance is sufficient. If required, increase the capacitor. I'd not recommend to use a bigger capacitor than 100pF.
    2. A too big capacitor influences transient response
    3. right. It decouples noise caused by the Power Safe pulses and features smoother operation for light loads.