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SN74AHCT244: Short time high output current

Genius 9105 points

Replies: 3

Views: 91

Part Number: SN74AHCT244

Hello,

I have a question for SN74AHCT244 output current for capacitive load.

The datasheet(SCLS228M) defines absolute max of “Continuous output current, Vo<0 or Vo>Vcc)” as +-25mA.
But in my customer’s system, the peak output current is around +-78mA due to 0.01uF capacitance of RC filter while it is very short time.
The below is the circuit and waveform.



Does the customer have to keep this continuous output current, +-25mA, even if the time over 25mA is less than a few us like this figure?  
Does they need to adjust RC filter parameter to keep the peak current less than +-25mA?

Regards,
Oba

  • Hello Oba,

    We recommend keeping the output load capacitance at or below 70pF.  If larger capacitances are to be used, a limiting series resistor should be added to keep the maximum current below 25mA.

    In this case, the 51 ohm resistor should be swapped for a 220 ohm resistor to keep the maximum current (assuming a 5V supply) below 25mA.

    If this is a filter circuit, the capacitor value can be adjusted to keep the same cutoff frequency.


    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.

  • Genius 9105 points

    In reply to Emrys Maier:

    Hi,

    Thanks for your answer.
    Where does "70pF" come from? I can't find any description about it in the datasheet.

    Regards,
    Oba

  • In reply to Oba:

    This is a recommendation from the standard logic applications team, not a set value in the datasheet.


    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.

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