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Startup up control on DC fan with TPS24750

TAN SB
Intellectual 400 points
Other Parts Discussed in Thread: TPS24750

Hi,

I am using the TPS24750 configured for 12A to control a brushless DC fan, the start-up inrush current is about 13A, the steady state current is about 6.5A. How can I configure the TPS to limit the startup current? Attached is the schematic.

Thanks,

SBTPS24750.docx

  • 0
    TI__Mastermind 42795 points
    Hello,
    I am moving this to the load switch forum.
  • 0
    TI__Guru** 105791 points
    Hi Tan,

    The internal power limit engine limits the inrush current and also power dissipation across the device to safe levels. As Rprog (64.9K) is configured for 21W power limit here, the inrush current gets limited to 2.5A typ. Alternatively, the startup current can also be limited by placing RC network at the GATE pin. Please refer to page 30 in the datasheet.

    Regards,
    Rakesh
  • 0 in reply to Rakesh
    Intellectual 400 points
    Hi Rakesh,

    I didn't see the problem when the fan module is first hot plug into the system where the Vcc starts the ramp up from 0V to 12V, I believe at this instant the efuse is limiting the inrush current. The fan is running at max rpm on power-up.

    Here's the problem that I am seeing, after power-up with the fan running at a steady state drawing about 6.5A, the fan is than ramp down to min rpm waited for it to settle than ramp up to max rpm, it is during the ramp to max rpm that the efuse trip. Based on the fan's spec sheet, the current during this ramp up time rises up to about 13.5A (the power up inrush current described above is a few amps higher than this).

    It seems like the inrush current limiting feature function only during the power-up cycle and not after.


    Thanks,
    SB
  • 0 in reply to TAN SB
    TI__Guru** 105791 points
    Hi Tan,

    After successful power-up, the GATE of the device is fully turned-on. So, the device responds only for the current-limit threshold or fast-trip threshold.
    In your case, when fan is ramp down to min rpm and then ramp up to max rpm, the load current may exceed the current-limit threshold.
    Please check whether the efuse trip is due to the circuit breaker operation by monitoring the charge timing capacitor CT voltage.

    Regards,
    Rakesh