I want some of the ESP32's GPIOs to be accessible via 3.5mm headphone jacks or RJ11 jacks and therefore need suitable ESD protection. I wonder how much is needed for optimal protection.
- The board is powered by a 12 V wall plug
- The voltage is brought to 3.3 V via a step down converter based on the LM2575
- 2 Layer PCB. The bottom layer is GND
- I want to protect against ESD strikes described in IEC 61000-4-2 (8kV contact, 16kV air-gapped)
- IOs should
- be working as inputs and outputs
- be working with a max. frequency of around 250 Hz
- have an output voltage/current enough to drive a bipolar transistor or MOSFET.
My initial idea
Roughly based on this digikey article and other resources found on the Internet I came up with these circuits.
However, I'm still confused by all the info floating around. Let me try to explain my thinking:
Assuming that I have a TVS diode with a clamp voltage between 8 and 16 V. E.g. the T3V3S5
In the event of an ESD strike, I therefore have to assume that the ESP32 is exposed to a voltage between around 8 and 16 V. Through the 1k resistor I want to limit the current so that the pulse for the internal diode remains manageable. Worst-case the internal circuit would have something around
16V-3.3V = 12.7V and
(16V-3.3V)/1000Ohm = 12.7mA to cope with, correct? Is that something the ESP32 would survive?
Can I assume that the circuit on the left is already sufficient to protect the ESP? In this case of course the ESP32's internal protection circuit is used. Or should I rather throw external diodes to it like in the example on the right?
Unfortunately I cannot find any documentation on the internal protective measures of the ESP32 GPIOs. If you have some info please let me know.
- Do the circuits make sense? Is one of them suitable to protect the ESP32?
- Will the step-down regulator be able to cope with the heightened power rail or do I need some more circuitry there?
- Should I rather use something like this to avoid latching up the PSU rail?
- What if the board is not powered?