Re: 74HCT outputs in paralell


"David L. Jones" <altzone@xxxxxxxxx> wrote in message
news:1125490862.084317.292540@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> 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 :)
>

Thats a good idea using a p/up p/down resistor, I should do that.
cheers
rob


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