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SN74AHCT244: output current

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Replies: 4

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Part Number: SN74AHCT244

We are trying to figure out if it would be acceptable to drive a MOSFET at a frequency of 20kHz using one of the output of a 74AHC244. We have captured the current waveforms during turn-on and turn-off, waveforms attached.

While the RMS is well within the Io spec. of table7 of the datasheet (“Limiting values”), the instantaneous current goes over the limit. I was wondering if the Io spec. refers to continuous current draw only or if it represent max. instantaneous current as well.

Would the following patterns present a reliability issue for the device if repeated continuously at a frequency of 20kHz.

Regards,

Doug

  • Hi Doug,
    There's no time limit on the absolute maximum ratings table for a reason. If one of those values is exceeded, we can no longer guarantee that the device will continue to function -- ie it could be broken on the very first time you exceed an absolute maximum rating.

    I would recommend using a device rated for the currents required. Perhaps a MOSFET gate driver?
    www.ti.com/.../overview.html


    Looking for a low voltage translator? Check out the AXC family that supports 0.7V to 3.3V translation!

    The Logic Minute training page has videos on many interesting topics that all are kept shorter than 5 minutes.

  • In reply to Emrys Maier:

    Hi Emrys,

    Can I just point out that Io is mentioned as "continuous output current" in the datasheet, not just "output current". Any specific reason for this wording?

    Thank you,

    Florent

  • In reply to Florent Boico32:

    That wording has been in place for about 50 years. I'm afraid I don't know why the original designers put it that way.

    Logic devices aren't really intended for power delivery, so it might have been an indicator for those that didn't know the difference.

    The fact is that the part will likely survive spikes like the one you showed, but I (TI) just can't guarantee anything beyond the datasheet specs.


    Looking for a low voltage translator? Check out the AXC family that supports 0.7V to 3.3V translation!

    The Logic Minute training page has videos on many interesting topics that all are kept shorter than 5 minutes.

  • In reply to Emrys Maier:

    Hi Emrys,

    I understand, thanks for taking the time to answer our questions.

    Best Regards,
    Florent

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