ESD & Lightning Protection

Other Hardware General Electronics
1

Hello there,

I am looking for some help about protecting microcontroller inputs against ESD, from human contact and lightning surges, etc. The microcontroller is the Arduino WAN 1310 (https://docs.arduino.cc/hardware/mkr-wan-1310)

The microcontroller used by the Arduino WAN 1310 is the SAM D21/DA1 Family (https://ww1.microchip.com/downloads/en/DeviceDoc/SAM_D21_DA1_Family_DataSheet_DS40001882F.pdf). Page 865 of 1115 describes the maximum ratings for the device for which the maximum supply voltage VDD is 3.8 volts, and the maximum pin voltage is VDD + 0.6 = 4.4 V. The nominal pin working voltage is 3.3V (to which Arduino say these voltages must not be exceeded).

Three pins are connected to an external resistive sensor buried in soil, two for power and one for reading the sensor. I would, in fact, like to protect all the pins on the board, in which there are 29 in total. Could you please tell me what component/s you would recommend protecting the microcontroller against ESD and what led to that decision (maybe some design calculations so I can follow in the future). We are going to be making many sensor-based devices like this and would like to get the ESD bit right.

The microcontroller works inside a plastic enclosure without a direct ground connection (as it will be battery operated). I do, however, have a metal plate in the enclosure which could be connected to Earth through a wire to a copper pole if this is needed to dissipate the energy from the recommended device. I don’t think the surge current passing through the TVS and back to a pin is a good idea, as the pins can only take a few milliamps at most (as per datasheet link above).

I have spent a few weeks trawling through datasheets trying to choose the appropriate TVS device or Gas Discharge Tube, but I keep going round in circles where my design calcs tell me the device I have chosen is not suitable (I’ve not much experience with protecting circuits against ESD and lightning surges). For extra information (maybe not needed), the sensors are simple resistive sensors with resistances ranging from 500 Ohms to 10 K Ohms, other sensors I am using implement RS485. I would like to protect each pin of the Arduino / SAM Controller against ESD and Lightning Surges.

Thank you for your time and I look forward to hearing from you.

2

https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.337.8981&rep=rep1&type=pdf

3

A big mistake if want any ESD and lightening protection. Plastic is an insulator and as such will quickly conduct static charges on it's surface. The ONLY viable plastic enclosures are aluminum coated with a solid ground connection.

Any external wires will be inductively coupled to a lightening strike, so all wires must go through a feed-through capacitor to absorb the pulse.

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Thanks for the info. I know I can use TVS diodes, but not finding any with a small enough clamping voltage.

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Thank you very much for these documents. Very useful. I have read a lot of docs, it’s just finding the components suitable for the low voltage controller.

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