ESD diode drop measurement

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npat_avr
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Posted by npat_avr: Wed. Sep 30, 2009 - 03:07 AM
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Hi Freaks,

This is part of a more general question I have asked in the off topic forum but I would like to get your opinions on an ESD diode voltage measurement. This is the diode internal to the IC. I am planning to use the AVR ADC to measure this 0.6-0.7V drop. I have already got the attached circuit working with a discrete diode (component)with a lower resistance(about 10K) value. The ESD diode needs about 10 uA current. Will the attached schematic be ok to perform this measurement using the AVR ADC? R = 10k.

Thanks.

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glitch
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Posted by glitch: Wed. Sep 30, 2009 - 03:19 AM
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given where you have connected the ADC, what exactly do you expect the ADC to measure?

Writing code is like having sex.... make one little mistake, and you're supporting it for life.

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npat_avr
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Posted by npat_avr: Wed. Sep 30, 2009 - 03:31 AM
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Sorry I have it wrong in the schematic. The ADC connection is below the 500K.

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Kartman
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Posted by Kartman: Wed. Sep 30, 2009 - 04:04 AM
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Why do you have the series R of 10K? This only serves to introduce more error into the measurement - you could remove it all together or add a 10-100nF cap on the adc pin and 0v.

Why are you wanting to measure this voltage? It will change with temperature.

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npat_avr
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Posted by npat_avr: Wed. Sep 30, 2009 - 04:08 AM
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Thanks, Kartman.

I understand it will change with temperature. However, an accurate measurement is not needed. I just want to check if the diode is present or is blown/shorted i.e. checking continuity on the pin.

So will this circuit work to get me the 10 uA to forward bias the diode so I can measure the 0.6 - 0.7V diode drop?

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Kartman
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Posted by Kartman: Wed. Sep 30, 2009 - 04:43 AM
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How do you propose to test these diodes in a real chip?

If the ESD diode is damaged, there's normally other collateral damage to the chip - its not like these diodes are a separate component - they're all on the one chip. I wonder about the validity of the tests.

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npat_avr
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Posted by npat_avr: Wed. Sep 30, 2009 - 08:35 AM
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I agree with that. I have some other functional tests as well. I am looking for a quick go-no go solution to check if a chip is working or not. If the diode is non functional, chip will be tossed.

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alwelch
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Posted by alwelch: Sat. Oct 3, 2009 - 01:38 PM
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If you ground the VCC/GND pins in the part under test then when you input a voltage into an I/O pin current will try to flow from the protection diode to the VCC or ground pin depending on the polarity of the applied voltage. So + voltage would test the + ESD diode, - voltage would test the - esd diode. A resistor in series with the applied voltage would allow measuring the voltage drop.

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bpaddock
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Posted by bpaddock: Sat. Oct 3, 2009 - 04:38 PM
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npat_avr wrote:
I agree with that. I have some other functional tests as well. I am looking for a quick go-no go solution to check if a chip is working or not. If the diode is non functional, chip will be tossed.

http://www.analog.com/library/analogdialogue/archives/41-11/esd_temp_sensor.html:

Quote:
ESD Diode Doubles as Temperature Sensor...used the protection diode to measure the junction temperature of the regulator during routine testing and evaluation. This temperature sensing technique can also be used on a high-speed op amp....

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npat_avr
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Posted by npat_avr: Sun. Oct 4, 2009 - 04:09 AM
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@alwelch,
That is exactly what I am using to test.

@bpaddock,
Thanks, that is useful piece of info.

Anyway I have got it working. I have to make some refinements but the concept is working. Thanks, guys.

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