I am using an Arduino Due based on the Atmel SAM3X8E ARM Cortex-M3. I need to use the ADC in a real world application, and I have some long cables leading to it, possibly some inductive effects and some short spikes in voltage at startup / plugging / unplugging of some external sensors, so I am looking at protecting a bit the ADC inputs.

From what I have been reading on other threads, for example ADC input protection? , the best solution is to use diodes to protect the pin from over and under voltage, and these are usually built in. From reading on more discussions, for example https://forum.arduino.cc/t/voltage-limiter-for-arduino-analog-inputs/450941 , it looks like these diodes are ok only as long as the current flowing through them is under a few mA. That would mean that to protect the ADC I would need to add a resistor between the ADC pin and the point to measure, to limit the current flowing through the protection diode in case of over voltage. Then the protecting resistor should be chosen as a function of the "max over / under voltage" I can expect so that the diode does not get too much intensity flowing through it.

Minor question: is this understanding correct, i.e. adding a well chosen protection resistor on the ADC input, in combination to built-in protection diodes, should do the trick?

Main question, I have been looking at the datasheet of the corresponding MCU ( https://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-11057-32-bit-Cortex-M3-Microcontroller-SAM3X-SAM3A_Datasheet.pdf ), but I cannot find any information about such protective diodes. Am I failing at looking at the right place in the datasheet (I am not used to reading this kind of datasheet, if you can point me to / help me understand / explain to me in simple plain language the content on this aspect it would be very helpful), or are such diodes not built in on this MCU, or other?

  • \$\begingroup\$ Yes. The protection system described with 2 diodes and resistance is classic for "light overloads". Typically used on some OPamps & ADC Converters' instrumentation. Resistance always takes up space on the die of the chip. \$\endgroup\$
    – user288518
    Jun 19, 2021 at 13:09
  • \$\begingroup\$ I agree that the protection circuits on the I/o pads are not disclosed in the data sheet. There must be protection, to withstand esd, but you don’t really know the details. Better to use external diodes, or better yet, buffer the input with a separate device ( I.e. op amp). Better be safe than sorry. You perhaps could get a some advice from the manufacturer. Have you tried them? \$\endgroup\$
    – user69795
    Jun 20, 2021 at 0:59
  • \$\begingroup\$ Ok, thanks for the confirmation. This is quite annoying that not documented... I would like to avoid the need for extra components (this is just a small project, and I solder a 'shield' by hand on some prototyping PCB). Will try to contact the manufacturer. \$\endgroup\$
    – Zorglub29
    Jun 20, 2021 at 8:39


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