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TPS62147: Input Inrush Current limit

Edgard
Intellectual 610 points
Part Number: TPS62147

Dear Engineers,

I have one concern about inrush current on input.

I desinged the board and measured inrush current.

Then I found large current "about 50A" occurred...

(please refer to the picture attached. Blue is input voltage, red is input current.)

I don't know the torelance of input inrusch current on TPS62147.

Is it capable for TPS62147? Or should I reduce the current?

Thanks at advance

Edgard

  • 0
    TI__Guru**** 191445 points

    Edgard,

    The switch current is limited to about 1.7 A typical for TPS62147.  Where and how are you measuring the inrush current?  Do you have a large bank of electrolytic capacitors on the input?

  • 0 in reply to JohnTucker
    Intellectual 610 points

    Dear John,

    thanks for your replying.

    I measured the inrush current at the point of VIN with a current probe. (EN is shorted to VIN)

    I attached the wire in order to measure the current from VIN to a +12V power source.

    Some capacitors are placed at the VIN, the total is 360uF.

    Is it necessary to prevent large inrush current? If so, how large is the limit current? 1.7A?

    Kindest Regards

    Edgard

  • 0 in reply to Edgard
    Intellectual 610 points

    Could anybody answer my question?

  • 0 in reply to Edgard
    TI__Guru**** 191445 points

    Edgard,

    Most likely the inrush current is only going into the input capacitors.  It is not passing thru the TPS62147 to your load.  I once worked on a military project where we were required to limit this type current.  Electrolytic capacitors appear as very low impedance when the applied voltage is zero.  This can cause large inrush current when an input voltage is initially applied.  We used a series resistor equal to Vin / I limit with a FET in parallel.  We used a circuit to sense the voltage across the input capacitor bank and turned on the FET once the input capacitors were partially charged.  I do not remember the exact details of the circuit as it was over 25 years ago, but it should not be too difficult for you to design.

  • 0 in reply to JohnTucker
    Intellectual 610 points

    John Tucker,

    thanks for your comments.

    Anyway, the current does not pass trhough TPS62147 as principal, my concern has been cleared.

    Kindest Regards

    Edgard