3.3V-5V level shifters

BTW, I thought you are from Germany, not from India.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

I third the LV parts, should be fine either direction. I vaguely remember something about Fairchild's tiny logic too.

Cheers

That would be open drain ...

Well, yeah, why? I am just not a digital guy. Just wanted to know what's popular with the others.

The Fairchild and OnSemi Tiny parts are mostly high-voltage tolerant on their inputs (as in well over Vcc) so work fine in the 5-to-3.3 direction.

Going the other way, they'll work but get warm, unless you use the Schmitt version, and then the levels might get iffy.

John

We had that argument before. Driving the 5V HCT inputs from 3.3V levels is the standard practice; the input gate cross conduction is about 1ma.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

The 74LVC1T45 could be a good idea, too. I'm using this chip and I know another company who uses it without problems. It converts a single signal, only, but if you'll buy three of it, it might be less expensive than one

I have some thermal images around here somewhere that are interesting... a cute little row of hot spots. Some of the faster parts can get downright toasty at 3.3 in, Vcc=5. The lower power/slower ones are usually fine.

I don't want to argue; I just want to warn people to be careful about this.

John

I expect they mean the driver on the bed of nails tester setup.

It has to overpower the pulldown to turn off the tri-state drivers in the chip so its other hand can drive the outputs of the chip.

If I didn't need that for testing, I'd use a 0R pulldown. (I use ones that don't show up on the BOM. The board vendor gives them to me for free.)

That's exactly one reason why I asked here. There is a flurry of devices out there and for some of them even the specs are iffy. Like one of them that I almost picked (the TXB0104). It requires a "stiff" drive of 2ma min. So it need a 1K pull-up when open and since the other guys insist on series terminators .... meeeep ... out. Whew.

Thanks, Frank. But it's >15c, ouch. Maybe ok on this design though but the LVC4245 is only around 30c. Placement costs are not such an issue out here.

On this section my layouter is probably just going to hit the autoroute button and then have a coffee :-)

Hey, 6:43pm means 3:43am in Germany. When do you guys over there sleep ... ?

How about the Fairchild 74LVX3245?

Currently it is a bit more work. The marketing of one of our clients has produced some flyers for a product, which will be presented at a tradeshow next monday and sent it to their end customers. I'm the programmer of the firmware and I was amazed to see all the nice features. Unfortunately only a subset was defined in the requirements specification. Now it's getting a bit more expensive :-)

Going from 5v to 3.3v is easy with Fairchild 74LCX541 and other parts in the family. I've found that Fairchild seems to have more interesting parts in jellybean digital, power FETs, and analog switches.

Mark

Don't we all know that? "Hey, we need this new thingamagic that we saw at a competitor and it's going to be easy, I think ..."

Ah, so now you can be found every night for dinner in the Kaeferschaenke :-)

Thanks. Looks like the LVC4245 which is probably what I am going to use.

AFAIK those are only 5V-tolerant but can't really drive 5V logic with gusto on the other side.

something like this then

it has dual supply, one for each side

-Lasse

Yep, or the LVC4245 I wanted to use.