esdremote controlreset
I would like to design a RC filter to prevent reset to a SoC during a ESD strike. Assuming the reset net is by default low.
And the reset comes from a separate board which connects to the main board (where SoC resides) using a Board to Board connector.
In case there is air discharge on the daughter board. I want to avoid changing the state of reset line during the ESD strike and avoid trigger of reset to the SoC.
I am not sure, what the question is, but i know what did you forget. You have also to protect the gate driver. This is because between the gate and the drain (and source) there is some capacitance which in case of ESD discharge will just conduct, so a voltage surge is possible on the gate.
upd. in case of such surge one of the implications may be opening the valve. not very nice.
What I think you need to do is make sure that the charge from the ESD pulse does not reach the MCU. You have done all the right things to try and absorb this charge.
However, the charge comes from a capacitor with a very low series resistance so you would need devices with a very low series resistance as well to be able to absorb the transient of the ESD charge. Also these devices need to be fast.
What I would try to do is to prevent the charge to flow into the MCU. So I would add a resistor in series with the MCU's reset pin. The MCU will also have ESD protection inside, this combined with this external series resistor and the components you already have should prevent the ESD pulse from resetting the chip. I would start with a 1 kohm resistor but increase it's value if needed.
As the reset input of your MCU will be high-input impedance the extra resistor will not influence normal performance. But it will increase it's ESD handling capability !
simulate this circuit – Schematic created using CircuitLab
Best Answer
Assuming the reset pin is pulled up, putting a 100nF cap to ground at the pin generally won't hurt you. The bigger issue here is ESD protection. Where is the ESD getting into the circuit? Cable shields, connectors, the enclosure, any user interface buttons or knobs, , etc. all need to be considered. The energy from the event needs to be safely dissipated, with the how depending on the source. I strongly recommend read through John Barnes' articles on ESD protection.