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Electronics => Beginners => Topic started by: RoGeorge on March 25, 2022, 07:27:03 pm

Title: Any benfits from a bipolar OpAmp w/o internal ESD protection?
Post by: RoGeorge on March 25, 2022, 07:27:03 pm

While searching for some generic bipolar OpAmps through my scrap boxes, I've noticed that Motorola has had two versions of the 2902:
- LMT2902 without internal internal ESD protection (stated so in the datasheet)
- and "normal" LM2902 with ESD clamping protection diodes included

Why so?  Why having two different dies for the same OpAmp?  Is there any benefit for having a non-ESD OpAmp?

Title: Re: Any benfits from a bipolar OpAmp w/o internal ESD protection?
Post by: TimFox on March 25, 2022, 08:43:30 pm

The internal diodes add extra capacitance between the two inputs, which can degrade high-frequency performance.
Of course, blowing up the input devices will degrade the performance further.

Title: Re: Any benfits from a bipolar OpAmp w/o internal ESD protection?
Post by: RoGeorge on March 26, 2022, 02:21:52 am

Could be.  Not sure if that would make a difference in a low speed OpAmp (1MHz unity gain bandwidth),  unfortunately the datasheet I found for LMT2902 has no AC specs.  DC specs are identical between LMT and LM versions.

I wonder how much extra die area is needed to add ESD protection diodes.  Maybe they just wanted to fit more chips on a wafer, only to realize later that the ESD resilience is preferred over a slightly cheaper IC.

Title: Re: Any benfits from a bipolar OpAmp w/o internal ESD protection?
Post by: magic on March 26, 2022, 07:57:53 am

Actually, I don't think I have seen anything special in LM358/324. There are TI versions on zeptobars.com and ST's TS321 and there used to be ST's LM358 on vintageteardown.com too but that site went down recently.

Except for some of the Chinese ones, which appear to have a second PNP similar to the input one but with grounded emitter.