Is there a part?

Two parts of same type (easy) or one part that has both in the same package (not easy)?

If two parts you could use 74HC and use two resistors to pull the threshold a bit for the 5V-supplied part to that 1.65V lands at 2.5V at its input. Wear a hard hat during the design review :-)

I'd be surprised if you're able to find this in one package, since you want the two outputs to run off of the two different power rails.

I might be tempted to perform the inversion using a dual 3.3V inverter -- something like this:

---Joel

You need a logic level translator, such as...

What speeds are you needing? ...Jim Thompson

Two parts. I checked for 74HCT single-gate parts on DigiKey and there were very few indeed -- AHCT, yes. HCT, no. I don't want to mess the customer up with parts that'll disappear next year (or next month!).

So, have you considered those 'pre-biased transistor' gizmos? The logic inverter function is very similar to a one-transistor switch.

So which part number will do both of the tasks that I've posed above? Currently I'm calling out a 74AHCT1G00 (wired as an inverter) for the 5V power, 3.3V logic input, and a 74LVC1G00 for the 3.3V power, 3.3V logic. But it's finding _one_ part number that'll go into _two_ spots that has me stumped.

Optical. Twinkie-light optical, that is. One is driving an LED, the other is turning an interface on and off. So something with a rise time of 100ms is _definitely_ too slow.

I couldn't see anything in there that does the two jobs I need to do with one part number - currently I'm calling out a 74LVC1G00 and a

Depending on the exact 3.3V logic levels, perhaps

---Joel

errr... ignore that, given that you're already using one. :-)

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can't use a transistor for driving the LED?

-Lasse

I need to put two tiny logic inverters into a design. One needs to run from a 5V supply and turn on from a 3.3V logic signal. The other needs to run from a 3.3V supply and turn on from a 3.3V logic signal.

I'd really like to use one part for this, but in my (admittedly fairly brief) searches I've found 74AHCT parts that work at 5V with 3.3V input, and 74LVC parts that work at either 3.3V with 3.3V input, or 5V with 5V input -- but not one that'll do what I need.

If you've solved this particular problem, I'm happy to hear your solution.

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Look up the I2S specification. A simple mosfet configured properly will solve your problem. I used this for level translation to drive a 15V signal from a 3V signal but it is bidirectional.

How about 74HC?

Lots of other mfgs, tons of stock. The one that is supplied 5V needs an input offset up front.

I considered that. I'd have to use at least one additional resistor to make it right (a 3.3V rail, a 2.0V LED, and a 0.65V BE drop don't leave me with enough headroom to be happy with an emitter follower, and a common-emitter stage needs the current limit on the base).

V_IH is 3.5V for VSS = 5V. That's a bit high for 3.3V logic. I could take Joerg's suggestion and use a couple of resistors to pull it down -- but in that case I'd just as soon use two different parts.

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| \ --- | \ | >------| >O------' | / | / |/| | =3D=3D=3D

-- Cheers, James Arthur

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didn't you say you had 5V supply too?

-Lasse

You need to pull up, not down. A cleaner alternative would be a transistor or FET, of course. But more expensive.

Didn't you want to avoid that because you are afraid your client would stuff wrong?

Diff receivers might be another option, where you could set the threshold by tying the other input pin to 1.65V and 2.5V respectively. But that costs four resistors. Or three if you really squeeze it. Three is still more than two :-)