Re: 8:1 Multiplexer IC that's faster than 74HC151?


"Jim" <me@xxxxxxxxxxx> schreef in bericht
news:T2k4g.61$k72.48@xxxxxxxxxxxxxxxxxxxxxxx
Hi,

I am after an 8:1 multiplexer IC (in fact I have 6 inputs to route to 1
output) and the 74HC151 would be ideal, except its propogation delay is
too long (33ns over -40 to 85degC) in this particular case. The inputs are
TTL but outputs of 3.3V would be fine, so I hoped there would be an
equivalent part in the LCX family for faster propogation (20ns max is what
we need). However, the 74xx151 seems only available in HC and HCT.

Is there another 8:1 multiplexer IC available, or can another logic IC
(e.g. a quad 2-input multiplexer) be connected in such a way to form an
8:1 multiplexer? I 've noticed a lot more quade 2-input multiplexers
available and they are also found in LCX family, unlike the 74xx151.

Many thanks,

--
Jim



Jim,

Philips had the 74Fxx series wich were much faster than 74LSxx, even faster
than 74Sxx. If memory serves power consumption was generaly between these
ones. The switching characteristics of some of them was somewhat special. I
remember the "first incident wave" characteristic which required some
passive components when you tried to control high impedant (in casu CMOS)
components with them. In one case I could not get rid of the reflections
even with short wires (traces). Nevertheless a 74F151 - if available - may
be a good choice. Another option is programming the devices yourself using
GALs or similar programmable devices. They also look like a litle bit old
fashioned these days but GAL22V10 are still available and come with
propagation delays below 10ns.

petrus bitbyter


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