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TPS25924: About internal MOSFET state in over-load current limit condition

Tsukui Yusuke
Guru 21930 points
Part Number: TPS25924

Hi,

When power is turned on, TPS259241 starts up repeating auto retry.
(Vin=9.5V Iout=2.4A condition)
Please check the attached waveform.



The internal FET when auto retrying is in operation can not be turned on completely.
And This operation is used to limit the current.
Is this understanding correct?


Best Regards,
Yusuke/Japan Disty

  • 0
    TI__Guru** 105361 points
    Hi Yusuke-san,

    What is the output capacitance? and the capacitor on dv/dt pin? Can you share me the schematic.
    The device is starting in current limit mode and resulting in thermal shutdown.

    Best Regards,
    Rakesh
  • 0 in reply to Rakesh
    Guru 21930 points

    Rakesh-san,

    Thank you for your response.
    Capacitance : 1uF
    dv/dt : 1000pF

    "The device is starting in current limit mode"
    Yes. Customer understands that it is starting up in current limit mode.
    Customers want to know how internal FETs generate heat.
    Is it correct with the understanding that FET is not turned on completely, and it is turned on a little bit.
    Please tell me the mechanism by which the following formula is applied.



    Best Regards,
    Yusuke/Japan Disty

  • 0 in reply to Tsukui Yusuke
    TI__Guru** 105361 points
    Hi Yusuke-san,

    In current limit mode, the device regulates the GATE of the internal FET to maintain constant output current. Yes, your are correct, the device is not turned ON completely. The power dissipation becomes (Vin-Vout)*Ilim

    What is the start load value (equivalent resistance)?
    Since the output capacitance is low, Please leave the dv/dt pin open and test.
    Please use the design calculation tool available at www.ti.com/.../toolssoftware to verify whether the device is able to do successful startup.


    Best Regards,
    Rakesh