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weird ways to damage a ad620 chip

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NiHaoMike:

--- Quote from: DiTBho on May 09, 2021, 04:47:02 pm ---One month ago I was surprised to see an envelop containing five "IXTH140P10T" sold for 35 euro including shipping. The IXTH-boy is a strong P-MOSFET, 100 V, 140 A, 0.01 ohm RDS_on, TO-247 package, a strong device for which Farnel asks 26,04 euro + postage for two of them.

Recently I have personally tested them. Five of five in perfect working order without a visible defect up to 10A of load.

Good! Happy ending! Or just lucky? Who knows, but for sure you are perfectly right, I have already different and different times to avoid buying electronic things on eBay, unfortunately for my colleague there is no worse deaf than those who do not want to listen.

--- End quote ---
Easiest way to detect fake MOSFETs is to check the RDSon, then checking if it can withstand its rated voltage. Most often, a fake would have a much higher RDSon. The rated voltage check then weeds out those that are cleverly remarked parts with similar RDSon but a lower voltage rating.

DiTBho:

--- Quote from: NiHaoMike on May 09, 2021, 04:52:23 pm ---Easiest way to detect fake MOSFETs is to check the RDSon, then checking if it can withstand its rated voltage.

--- End quote ---

Yup, the low RDS_on is exactly the reason he bought those MOSFETs, so it was the first thing I checked during my tests :D

DiTBho:

--- Quote from: Ian.M on May 09, 2021, 04:48:42 pm ---He's also got Vref grounded which is only permissible (for normal operation) if -Vs (his Vee) is at least 1.6V below ground, but that's also tied to ground.  However I doubt that would cause damage as if it could, there'd be limits for Vref in the datasheet's ABSOLUTE MAXIMUM RATINGS section.

--- End quote ---

Thanks a lot for this clarification!

DiTBho:
I have hust tried the other two AD620 units my colleague bought from eBay. These two were in perfect working order with my circuit (Vee=-5, Vcc=5V, Vref=2V) so I have tested them with my colleague's procedure, and it seems they are very fragile. Connecting Vref to gnd showed two effects


* it has forced the chip to eat 12x more current, I measured 12mA instead of less than 1mA
* it has - somehow - damaged the chipI won't repeat this test with the two new fresh chips ordered from Farnel. I am also moving from AD620 to AD623, this one is better for my colleague's needs.

amyk:
The increase in power consumption suggests latchup.

If you still have the damaged ones, there's some other forum members who might want to get die photos...

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