Schottky diodes have higher V drop than PN?

Typical ESD for 'HC'... can vary from part-to-part and whether the device can stay on a bus with the power off...

Series resistor from input pin to circuit and ESD

Upper diode is the body diode of a PMOS.

Lower "diode" is an NMOS device, source AND gate grounded, drain to circuit-side of input resistor.

There is often some fancy additions to help prevent latch-up.

For a situation where the input comes from "off-card" an additional series resistor is all that is generally needed.

I haven't studied the models in question, but Schottky's are low drop only for moderately low currents.

...Jim Thompson

Fewer, actually.

Good, because it ain't true.

John

No, but the idiots here know how to spell 'forum'.

Jim

But at least the datasheets specifically state it can tolerate the IEC ESD standards.

This leads me to wonder, since so many semi datasheets state that the devices are not intended for use in life-support systems, etc., how do you medical equipment designers find any parts at all? Or do you make special legal arrangements with the manufacturers to absolve them of any liability then they'll sell you whatever you want?

Good day!

I looked at all the 1N4148 datasheets I have, and only one, the original GE one, shows any information about surge capability. The GE sheet has a transient thermal impedance curve, from which you can derive the surge capability. Shall I post it over on ABSE?

Hello Chris,

I was just eyeballing the 70mA. But 57mA is equally dicey to jam into an HC input.

Maybe but with currents of this magnitude I'd pick a large diode pair.

Since I work mostly in med there either is mfg data in writing on that or I can't do it. Similar to aeronautics and other critical apps.

Pretty expensive. It may be better to select a beefier pair of regular diodes. Slim pickings though and companies like ON Semi do not list current ratings on their parametric tables, for whatever reason.

Regards, Joerg

Hello Jim,

Depends on where they live. In the mountains it's sometimes pronounced "furrum" ;-)

Regards, Joerg

Hey Chris, Funny, I'm using 74HC14 gates as input line receiver in an avionics job. The inputs are from 28V/GND relays so I use a 100K input series protection resistors and a lot of filtering. The customer does not believe it is rugged enough to handle 32V inputs. I say +/- 2KV or until the 100K resistor smokes but he's not buying it. What a life!

cheers, Harry

Hello Chris,

Well, yes, but there are less expensive ways (big diodes).

We don't do any life support designs without a waiver. Companies that do often produce their own semiconductors. Seriously, I have seen a company run their own transistor and logic chip production. They test the dickens out of every single part. Of course, a 10c chip will then become a $10 chip. Now you know why pacemakers are so freaking expensive ;-)

Regards, Joerg

Hello Harry,

If the customer doesn't know electronics that will require a lot of s'plainin'. Just like my EMI sermons. Takes forever to sink in. It's like talking to marketing folks although the results can be very different there. The first time I had to do that in my career resulted in marriage ;-)

Oh, and we are still married.

Regards, Joerg

For audio balanced line inputs I use a 470R followed by a BAT720S to the rails. There are 12VMOVs across the rails to absorb the injected current before the 22V rated opamps get destroyed. I also put a 1n cap after the

Sorry I mixed up the number

Joerg ...

I did the same thing, only mine was a forum after which this little Chicago blonde and I "disagreed" on a technical point.

Today is our 8th anniversary.

Jim

The first time I had to do that in my career resulted

REALLY bright women are the preferred embodiment !-)

...Jim Thompson

Hello Ban,

That is a good diode but 45c isn't exactly cheap. I could only see it at Philips (I wish they would stop that stupid stock quote wait on their site, when do they learn?). Single sourced?

It does cave in around 2amps but that may be ok if there is another resistor between the BAT140S and the device pin.

Regards, Joerg

Either that or a good bar-be-que. Man can't have both. Cheers, Harry

ROTFLMAO!

Bwahahahahahaha

Cheers Terry