• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 63 subscribers
  • Views 133 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.

TPS22990: Maximum allowable start-up current

ChienMing Chiu
Prodigy 20 points
Part Number: TPS22990

Hi there,

Do you have maximum allowable start-up current for TPS22990N?

I'm asking this because I saw huge inrush current forced TPS22990N to turn off, so I want to calculate the feasible soft-start time.

I know the total capacitance after the TPS22990N and I also know the working voltage, and I can use the equation to calculate it if I can get the maximum allowable start-up current.

Thanks

ChienMing

  • 0
    TI__Genius 14225 points

    Hi ChienMing,

    Welcome to E2E!

    Due to the way the max pulse is characterized we're unable to provide a calculation that would offer the same guarantee that is offered from the specification in the D/S. 

    I think the best option is to utilize the adjustable slew rate feature of the device. The TPS22990 has very fast timing without a CT capacitor (CT). I would recommend placing a CT capacitor on the CT pin, considering the minimum voltage rating for the CT capacitor should be at least 30 V for optimal performance

    This is of course assuming the inrush current occurs during turn on of the device. If the inrush current occurs after passing a UVLO setting of a downstream device or based on some other event, then slew rate control would not mitigate this and you would need to use a higher current rated device.

    Best Regards, 

    Elizabeth  

  • 0 in reply to Elizabeth Higgins
    Prodigy 20 points

    Hi Elizabeth,

    Thank you for your reply.

    I did place a CT capacitor to extend soft-start time, I was able to calculate inrush current with following equation:

    I =C * (dV/dt)

    That gives me a 5.11A of inrush current.

    The larger CT capacitor the slower of soft-start time, it also trimming the maximum allowable current during the start-up.

    That's why I'm looking for maximum allowable start-up current since there is no SOA (safe operating area) in datasheet.

  • 0 in reply to ChienMing Chiu
    TI__Genius 14225 points

    Hi CheinMing, 

    Could you send me your schematic? If your VIN pin is tied to your ON, there could be a situation where a large output capacitance would cause an input voltage dip pulling the ON signal below the VIL threshold around 0.5V causing the device to turn off. 

    If your VIN is not tied to ON, please send scope shots of VIN, ON, and VOUT during this fail scenario. 

    Best Regards, 

    Elizabeth