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Peak fault sink current TPS2557

Knut Olav Skyttemyr
Intellectual 290 points
Other Parts Discussed in Thread: TPS2557

Hi, I have a question regarding maximum current into the fault pin on TPS2557.

In the datasheet, you state an absolute maximum continuous current of 25mA, but there is no information about maximum peak current. The current is drawn from a discharging capacitor, so the current will quickly fall off.

I need this information to compute the correct current limiting resistor value into the fault pin, and I want don't want to oversize this resistor.

best regards

Knut Olav

  • 0
    TI__Expert 7990 points

    GIven the continuous rating, the pin should be able to sustain 2x the current for a short time (50mA).  Original simulation data predicted a resistance range of 36 to 122 ohms over the full temperature range with a simulation typical (25C) of 67 Ohms.  There was a significant temperature cooefficient in the collected data that looked to be about 1.5% / C based on the mean data points.  Note that the tempco and resistance range don't line up since they are from different sets of data, with one based on means and the other on mean to max.   There is some possibility that the output device might saturate, but most likely not at this current.

    For a 5.5V output, a limit resistor of 75Ohms (5.5/.05 - 36) should do if the full temperature range (and insignificant self heating) is considered.  Adapt the computation to your application.

  • 0 in reply to Martin Patoka
    Intellectual 290 points

    Thank you for the reply!

    I understand 5.5 V / 0.05 A, but I struggle to understand why you subtract 36.

    In my application I use 3.3 V input/output of the TPS2557.

    best regards

    Knut Olav

  • 0 in reply to Knut Olav Skyttemyr
    TI__Expert 7990 points

    The calculation computed the total resistance to limit the current with 5.5V applied, and by subtracting the minimum device resistance obtain the required external resistance.

  • 0 in reply to Martin Patoka
    Intellectual 290 points

    Thank you for the clarification!