did I damage my op amp

Without much forethought, I used my DMM to measure the resistance of the 24k resistor in the following circuit under development (red lead to the V+ pin end, and black lead to the + input pin end). There was nothing else attached to the LM258 or resistor at the time.

Later, I realized that the DMM applied a negative voltage to the + input relative to the the Vcc pin. The DMM apparently uses 100mV to check resistance (measured using my other multimeter - an analog one - by just attaching lead to lead).

Judging from the schematic, I would have forward biased the emitter-base junctions of the input transistors and the current source. I suspect that the voltage drop across those junctions is larger than 100 mV; if so, then there would not have been any current flow…and no damage. Right?

Also, this situation would be no different than having a voltage lower than V+ at one of the inputs (normal powered operation), except that in my case, the chip wasn’t being powered in the normal way.

Thank you,
Dave

PS: The first attachment is the schematic shown above. The last two attachments are excerpts from the datasheet with maximum values - I don’t think the negative voltage limit is applicable, since it’s with respect to ground.

PPS: I haven’t finished the circuit or tried it, yet.

It's extremely unlikely, nearly impossible, that any damage was caused by this.

I can't think of anything that would be damaged by measuring resistance.

You can damage things if you measure current incorrectly, because an ammeter is essentially a short-circuit. But in that case, the thing that usually blows is the fuse in your multimeter.

I have burned-up an op-amp by powering it with reverse-voltage.... Flames literally came-out! It was rather spectacular! I think I still have the breadboard somewhere, slightly melted with a brown spot.

You can also kill an op-amp with excess voltage (including a static discharge), or by "pulling" too much current from an output.

Does the data sheet give any specs for reverse voltage?

For damage to occur, you almost always need some current flow. 0.1v isn't usually enough to result in a significant current flow - you'll usually see this in the datasheet's absolute maximum specs. Usually they say -0.3 ~ -0.7 V minimum (depending on the process involved), and the same amount above Vcc as the other limit. And, consistently with this, I've never heard of a part failing because of performing measurements on it with a multimeter (obv not counting cases where you short something with the probes while it's running - I've burned out a couple things that way)

DVDdoug: I have burned-up an op-amp by powering it with reverse-voltage.... Flames literally came-out! It was rather spectacular! I think I still have the breadboard somewhere, slightly melted with a brown spot.

Where there is fire there is 'Magic Smoke™'.

Thanks everyone - appreciate the help.

outofoptions:
Does the data sheet give any specs for reverse voltage?

Yes, abs max reverse voltage is -0.3v, but as my “PS” noted, that’s relative to ground. In my case, the voltage was negative relative to the V+ pin, and the ground pin was floating.

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Let's look at this another way. You have some transistors and diodes and one capacitor in one package. The reverse breakdown voltages are generally pretty high. Just look up any 'typical' diode and transistor. 2n2222 is something like 70V. That leaves one cap and there is no indication it is polarized and even then the voltage of 100mV is pretty small.

Ok, thanks for the help.

You could test it with a simple Vin = Vout circuit. I HAVE blown up 2 amps in a quad OPA4342, I believe by powering the + input without a good Vcc and GND connection. They never gave good results after that, but the other two amps continue to function flawlessly. Just that once though.

The multimeter has a "diode test" function. It applies more voltage than the resistance ranges and quite possibly, more current.

What you have done is to test the input diodes in your IC. Either they conducted or they did not. That's it - nothing more, nothing less.