Re: 74HCT outputs in paralell

Rob wrote:
> "David L. Jones" <altzone@xxxxxxxxx> wrote in message
> news:1125485615.270243.89080@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> > Rob wrote:
> > > Hi all, I'm using a 74HCT240 tristate inverting buffer, is it ok to
> connect
> > > outputs together? - the inputs are also connected together.
> >
> > You can do this, but normally you wouldn't, as doing so will increase
> > the power consumption if the inputs are switching.
> >
> > > I don't need extra drive, I just have some spare gates.
> >
> > Then just tie the inputs to a rail and leave the outputs floating, that
> > is standard practice.
> >
> > > I could not see anything in either the device or HCT family data sheets
> in
> > > relation to doing this.
> >
> > That's because it's not standard practice.
> >
> > Dave :)
> >
>
> Thanks for the help Dave.
>
> I'm a bit of a master of "non-standard" practices.... : )
> rob

You can often do lots of useful stuff with non-standard practices! :->

BTW, I hope you didn't mean just connecting the inputs together and
*not* connecting them to a rail as well? That's bad.

Actually, it can be good practice to connect the inputs via high value
resistors (say 1M) to ground (or Vcc) instead of just tying them hard
to the rail. In this case it means that you can use the gates at a
later stage without cutting any PCB tracks, simply wire your signal up
with some mod wire. If cost and board space etc isn't an issue then it
can come in handy.
Oh, and if you are going to hard tie the rails, then leave some track
length so you can cut the tracks if you need to. If they are connected
via tracks under the chip then you have to start lifting IC legs to
isolate the pin if needed - yuck.

Dave :)

.