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CSD22202W15: Questions about inrush circuit design with CSD22202W15

david wei
Prodigy 10 points
Part Number: CSD22202W15
Other Parts Discussed in Thread: TINA-TI

Hi I am design an inrush circuit as shown in the image. The voltage is 3.3v (QSFPDDPLUG33 and QSFPDD33). Can the circuit work?

  • 0
    TI__Mastermind 31845 points

    Hello David,

    Thanks for your interest in TI FETs. I am assuming the input is QSFPDDPLUG33 and the output is QSFPDD33. Is that correct? I created a simple TINA-TI simulation (attached), left out the ferrite beads and schottky diode and increased the value of R585 to 1MΩ. Please see below. I applied a 3.3V ramp with a rise time of 10μs and it seemed to work OK. Let me know if you have any questions.

    CSD22202W15.TSC

    Best Regards,

    John Wallace

    TI FET Applications

  • 0 in reply to John Wallace1
    Prodigy 10 points

    Hi John,

    Yes, you're correct. The input is 3.3v QSFPDDPLUG33 and the output is QSFPDD33. The simulation looks good. One question is about value of R1 (R585), 1MOhm. It's very large value kind like open circuit. What would happen if I do one of the following:

    1. Remove R585 completely. Or

    2. Lower R585 to 100K or 10K

    Thanks,

    David

  • 0 in reply to david wei
    TI__Mastermind 31845 points

    Hi David,

    R585 pulls the gate up to the source to make sure the FET is off at initial startup and also forms a resistor divider with R576. I sized it at 1MΩ to minimize the current flow thru the 2 resistors while maximizing VGS to fully turn on the FET. I would recommend keeping the resistor and not reducing to less than 100kΩ.

    Thanks,

    John

  • 0 in reply to John Wallace1
    Prodigy 10 points

    Thanks a lot, John.

    David