SN74AHCT244: Short time high output current

Oba

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

over 4 years ago

0 Emrys Maier over 4 years ago

TI__Guru* 96591 points

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.

0 Oba over 4 years ago in reply to Emrys Maier

TI__Genius 15770 points

Hi,

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

Regards,
Oba

0 Emrys Maier over 4 years ago in reply to Oba

TI__Guru* 96591 points

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

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SN74AHCT244: Short time high output current