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TPS25910: Gate capacitance minimum

Darren Jenkins
Genius 10996 points
Part Number: TPS25910
Other Parts Discussed in Thread: TPS24751

Load switch team,

Our customer is using TPS25910 with a resistive and inductive load. They see it hit power limit very often during turn on, sometimes backing off many times and not having a predictable turn-on time.

I’m considering if it would be helpful to have a faster turn on time, so the Vout rises before the current, avoiding the power limit. They are currently testing with Cext (gate) at 1nF. The datasheet shows minimum External Capacitor, GATE is 1nF in the ROC. Other parts of the datasheet imply that the external capacitor is optional. Can this capacitor be removed to shorten turn-on time?

Thanks,

Darren

  • 0
    TI__Guru** 102091 points
    Hi Darren,

    The TPS25910 device has constant power limit of 5W (typ). So, it should be able to provide only 5W/(Vin-Vout) current at startup and gradually increases with Vout.
    What is the load at startup? inductive load -> is it a FAN load?
    As such the minimum External Capacitor at GATE is not critical. Please check with out 1nF at GATE.

    Best Regards,
    Rakesh
  • 0 in reply to Rakesh
    TI__Genius 10996 points

    Hi Rakesh,

    Yes the load is a fan.

    Yes, it is limiting the power during startup, but the problem is that under some conditions the gate is backing off significantly.  This lowers the Vout significantly since the current lags, and the cycle starts all over since there is little capacitance on Vout.

    Do you have any other recommendations?  Any thoughts on adding some bulk capacitance on Vout?

    Thanks,
    Darren

  • 0 in reply to Darren Jenkins
    TI__Guru** 102091 points
    Hi Darren,

    TPS259241 and TPS24751 devices are suitable for FAN loads. We have app note covering this use case. Please look at www.ti.com/.../slva683a.pdf
    The internal fixed power limiting function of TPS25910 does not provide flexibility to use for FAN loads.
  • 0 in reply to Rakesh
    TI__Genius 10996 points
    Thank you Rakesh. This was very helpful.

    In this case the power supply is not current limited. The only challenge is the load switch hitting the power limit. Removing the Cgate helped and might be the final solution.

    I need to send you some information by email. Thanks for the help on the forum.

    Darren
  • 0 in reply to Darren Jenkins
    TI__Guru** 102091 points
    Hi Darren,

    Thanks!. will follow-up on email.

    Best Regards,
    Rakesh