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TPS25923: I_fastrip value

Roy Chou1
Genius 13645 points
Part Number: TPS25923

After I read the document, Ihave some question about efuse.

  1. Question : I_fastrip accuracy formula in calculation tool. What is source of 20%. I couldn’t see the related information in datasheet.
  2. Question : Meaning of I_fastrip value. Below is figure from TPS25923, is I_fastrip value means peak value of I_out and I_clamp current is ISC current?
  3. I know below is TPS259241 measurement, but I also have a question about why you measure the Iout. Because Iout may influenced by output cap energy, so I think measure the Iin is the suitable way. (Iout peak shows 30A. I think that isn't real current pass through MOSFET)

Thank you for your help.

Roy

  • 0
    TI__Guru** 102711 points

    Hi Roy,

    1A) 20% variation is taken from the design considering the circuit configuration and its parameter tolerance.

    2A) I_fastrip is a threshold where the short circuit protection circuit starts working... but due to delays (internal circuit + FET turn-off) the Iout can go even large...

    IOL is the clamped current in overload and Isc is the clamped current while recovering from short circuit event

    3A) this test was done with out Cout hence output cap energy won't come into picture. What you see in the test waveform is the large current due to delays mentioned in 2A

    BR, Rakesh

  • 0 in reply to Rakesh
    TI__Genius 13645 points

    Hi Rakesh,

    Thank you for your reply. I still have some question below

    From 1A)  Did TPS25923 datasheet mention the 20% variation? Because customer challenge this 20% variation and consider that 20% is too large and wasn't inform by datasheet.

    From 2A) I saw the short circuit protection using specific comparator which has fast response. The figure shows the peak current is 30A. That means MOSFET in efuse could support 30A spike current? besides delay factor, do you have any idea that why cause this such hugh current? Because customer wouldn't like to see this result.

    Roy

  • 0 in reply to Roy Chou1
    TI__Guru** 102711 points

    Hi Roy,

    20% is not guaranteed parameter for I_fastrip and it does not need to be.. because a short circuit event creates multi-fold current much above the I_fastrip typical threshold.

    Please let customer know that large peak currents are expected (for any device irrespective of manufacturer) when you do low impedance short. The devices supports such peak currents for shorter intervals (<5us typ).

    Best Regards, Rakesh

  • 0 in reply to Rakesh
    TI__Genius 13645 points

    Got it.

    Thank you for your help