• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 62 subscribers
  • Views 473 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.

TPS55330 about Css Discharge Time

Hidekazu Fujikawa
Intellectual 460 points
Other Parts Discussed in Thread: TPS55330

Hello,

Please see attached and advice me.

TPS55330_SS-DischargeTime.xlsx

When the soft start capacitor value is 0.1uF, 

its discharge time is different between Case-A and B.

Case A: EN = Vin OFF

Case B: EN only OFF

Please tell me why these differences occur.

Best Regards,

H.Fujikawa

  • 0
    TI__Mastermind 35115 points

    Hi Fujikawa-san,

    Sorry for the long delay. I need to get an IC designer's input to answer this question.

    Based on the time scale the SS voltage looks to be charging up much slower and the capacitor may be more like 1 µF. Is 0.1µF the right value for the SS capacitor?

    When pulling only EN low with a large SS capacitor (1 uF) the SS voltage can discharge to only about 0.5 V. This would result in the long decay seen. If 1 µF or greater SS capacitor is used I recommend adding a resistor (about 300kOhm) in parallel with the SS cap to help discharge the remaining voltage. Adding this resistance may also slightly increase the soft-start time.

    When shutting down both VIN and EN, this looks to help discharge the SS voltage completely.

    Best Regards,
    Anthony

  • 0 in reply to Anthony F
    Intellectual 460 points
    Hello Anthony-san,

    Thank you for your reply and answer.
    It was resolved by turning OFF both VIN and EN.
    Thank you.

    H.Fujikawa