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SN74LVC2G07-EP: Abs Max Sink Current

Steve Widener
Genius 9805 points
Part Number: SN74LVC2G07-EP

In the situation at hand, the output of the SN75LVC2G07-EP has a 20kohm pull-up to 3.3V and a 0.1uF capacitor to ground. Vcc is 3.3V.

Can the SN75LVC2G07-EP safely discharge the 0.1uF without a chance of damage to the part? The situation only occurs on power-up / down of the system so this is not a high speed event - perhaps only a few times per day, not at high frequency. We see that there is either a 50mA or 100mA abs max rating for the part.

What capacitance would be too much and cause damage to the device?

  • 0
    Guru 256520 points

    When the discharge begins, the full voltage (3.3 V) is dropped over the buffer's output impedance (about 12 Ω). In that instant, a current of more than 250 mA flows. The RC time constant is 1.2 µs, so the time where the current is too high might be too long.

    To limit the current to 50 mA, the impedance must be at least 66 Ω, so add a 56 Ω or larger resistor.

  • 0
    TI__Guru 62930 points

    Steve,

    I went to check with my counterparts, and they indicated that with a larger capacitance they do recommend limiting the current.

    The issue is that we do not have a transient limit defined for max current.

    I will retract my previous answer and recommend a series resistance to keep current under the 50mA.

    Sorry for the confusion.

    Regards,

    Wade

  • 0 in reply to Clemens Ladisch
    TI__Genius 9805 points

    Clemens -

    This has already occurred on manufactured boards that have been extensively tested. We have done IBIS simulations that indicate about 200mA peak current that is in line with you guidance. Is it likely those devices could have been subjected to some damage? Please carefully advise as if there is a likelihood of damage leading to a latent failure (the walking wounded syndrome), we would need to advise rework and retest / validation of those circuit cards at system level.

    Steve

  • 0 in reply to Steve Widener
    Guru 256520 points

    Electromigration is accelerated by high current densities at high temperature over time. With 400 % of the absolute maximum rating for a nontrivial amount of time, these are exactly the circumstances you have to be afraid of.