1
\$\begingroup\$

I asked a question earlier question, "Is it safe to run Logic ICs at their maximum output current?" asking if it was safe to run logic ICs at their maximum current.

From what I understand, this is not a good idea and instead I should use some sort of 'driver' between my logic system and my displays.

After some searching I found the SN74HC244N however, this only has a maximum output current of 6mA at 5V (unless I'm reading the datasheet wrong). This doesn't seem very high to me for a 'driver' IC.

This got me thinking as to why I would want to use one of these chips as opposed to 8 transistors (which I assume could handle higher currents). Is it just ease of use that they are already in one small package or is there something I'm missing here?

\$\endgroup\$
1
\$\begingroup\$

It is a "Line" driver, as in to drive a bus with many other ICs that the previous part of the circuit can't drive.

It has:

  • clear I/O Low/High voltage levels,
  • low current requirement for input, (with a transistor you need a base current)
  • clear propagation delay and push-pull output, (with a single transistor you have open collector or emitter)
  • enable pin, so you can have many different drivers drive the same lines (i.e. 64 outputs and 8 inputs, then you enable one driver at a time)
  • etc

So its a "driver" for specific purposes on circuits, not a generic driver for LEDs. (There are darlington arrays for example that are made to drive loads, see ULN200X for example).

In essence you are kind of looking at the wrong part for the job.

\$\endgroup\$
  • \$\begingroup\$ Short propagation delay, if any. \$\endgroup\$ – Janka Nov 23 '18 at 23:09
  • \$\begingroup\$ @Janka - yeah I never do anything fast enough to have to worry about that, but "short" or "long" is application relative so the most precise thing I can say is "clear" (as in stated in a datasheet) \$\endgroup\$ – Wesley Lee Nov 23 '18 at 23:10

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy