• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 63 subscribers
  • Views 119 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS61390: max allowable capacitance on VSP pin

Ace Wu
Prodigy 20 points
Part Number: TPS61390

Hi TI guys,

When I'm using TPS61390, I want to put bigger cap on VSP pin than 47pF in EVM to better filtering noise.

Could you recommend the max capacitance allowed on VSP pin? So that I could make sure my hardware design is in the safe range.

Thank you!

  • 0
    TI__Genius 11150 points

    Hi Ace,

    Usually the cap in the EVM user guide is recommended. In your case bigger cap is needed for better noise filtering.

    It's hard to set a maximum allowed cap, for it's a tradeoff between noise filtering and sample-voltage setup.

    Suppose a extremely large cap is used, then a wrong voltage may be sampled before the right(final) voltage is achieved.

    A general way is: increase the cap gradually, if the requirement of noise filtering can be met, and the voltage at VSP can be stable at the final value, then the cap will be the suitable one.

    Regards

    Lei   

  • 0 in reply to Lei Zhong
    Prodigy 20 points

    Hi Lei, 

    Thanks for your input. I could do tradeoff between cap size and settling time myself. That's definitely OK.

    But my question is every amplifier has a max capacitive load it could support. Since there's an amplifier inside VSP pin, the pin should also have a max capacitance supported. If higher than that value, VSP output will be unstable.

    Could you provide that max capacitance number?

  • 0 in reply to Ace Wu
    TI__Genius 11150 points

    Hi Ace,

    Got your point. Thanks for the explanation.

    I'll check and get you the feedback tomorrow.

    Regards

    Lei   

  • +1 in reply to Ace Wu
    TI__Genius 11150 points

    Hi Ace,

    The maximum cap in VSP pin that our designer suggested is 100pF. Exceeding this value may result in low phase margin and much transient ringing in the internal amplifier.

    Regards

    Lei