CD74HCT240: Difference between output drive between CD74HCT240M and SN74HCT240D

Niral Kalavadia

Part Number: CD74HCT240
Other Parts Discussed in Thread: SN74ACT240, CD74ACT240, SN74AC244, SN74AC240, SN74ACT244

Hello,

I have refer datasheet of both the part mentioned in subject, from datasheet of CD74HCT240M I understand that each output can sink and source 25mA however same information(per output sink and source capability) I am not able to obtain for SN74HCT240D from datasheet.

My design requires sourcing 18mA current from each output pin. Requesting some information from community member

Regards,

Niral

over 3 years ago

0 Clemens Ladisch over 3 years ago

Guru 298540 points

The absolute maximum rating is not helpful for normal operation. HC outputs have a guaranteed maximum voltage drop only for 6 mA.

Use the SN74ACT240/CD74ACT240.

0 Niral Kalavadia over 3 years ago in reply to Clemens Ladisch

Prodigy 10 points

Hi Clemens,

Thank you very much for your answer.

Can the part number you suggested provide 18mA without voltage drop from every output at a time?

0 Clemens Ladisch over 3 years ago in reply to Niral Kalavadia

Guru 298540 points

All outputs have a voltage drop. But that of AC outputs is smaller; see the V_OL/V_OH specifications. Also see [FAQ] What is the output voltage (VOH or VOL) when the output current is X or the supply voltage is Y?

0 Clemens Ladisch over 3 years ago in reply to Clemens Ladisch

Guru 298540 points

What is your actual application? Do you need separate outputs, or 144 mA total? At what voltage?

0 Niral Kalavadia over 3 years ago in reply to Clemens Ladisch

Prodigy 10 points

Application is 8x8 dotmatrix driver. Each Output is connected to anode of 8 column of LED in dotmatrix array so output must source 18mA to LED.

Currently I have used 74HCT240D but not getting enough brightness even if I use 20OHM resistor and I have found that voltage is getting dropped same as you mentions in earlier post.

0 Clemens Ladisch over 3 years ago in reply to Niral Kalavadia

Guru 298540 points

Then the ACT240 is a good solution. If the input signals are not TTL, you can use the SN74AC240 instead. For a non-inverting buffer, use the SN74AC244/SN74ACT244.

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CD74HCT240: Difference between output drive between CD74HCT240M and SN74HCT240D