How to protect Reset pin of MCU from ESD strikes?

[SoonuVerma]

Hi Experts,

I'm using STM32F407 MCU, in a bot where I have seen ESD due to (friction/movement) in the bot, and this ESD reset my MCU several time unexpectedly.

So I would like to know an ESD protected reset circuit for the board

any other suggestions for protecting the complete board from ESD, as of now I'm using SP7538PU IC for protection of board from pins coming from sensors or external units.

looking forward for some valuable assistance over the same.

Thanks in advance.

[Danish1]

Do you know what is causing the processor to reset itself?

It could be a glitch on the reset pin on the processor. Does that pin go anywhere on the pcb? For example to a debug/programming connector, or a reset button. This can be damped by adding a capacitor between this pin and Vss; I typically have 0.1 uF. And I also have a 10k pull-up resistor to Vdd.

But it also could be glitches in Vdd. If you're switching motors on and off, when you turn them on the present a huge current-drain and that could be causing Vdd to drop - particularly if everything runs from a coin cell, causing the reset.

And when you turn them off, there could be a nasty spike much the same way as if you were switching off a relay coil. And these could find their way in on any pin.

I have also known processors reset when there is noise coupled into the oscillator / crystal pins, although I might imagine that a bot might just use the internal oscillator.

Hope this helps,

Danish

[Sirac]

Hi,

first of all, connect correctly your board to GND and if you can, put the board on a metal box. If you can't, you have to use TVS diode on any I/O you use.

[SoonuVerma]

Hi Danish and Jordan,

Thanks for the kind suggestion,

In my board Reset pin is connected to reset circuit which consists of 100nf cap in parallel with a switch and 100k pull-up resistor as well as to the JTAG connector, so is there any recommended change required in RST circuit or with this connecting a TVS diode will be good enough.

Danish there might be either of issues you have mentioned above but I was suspecting over ESD mainly because, there's lots of ESD generated while microfiber attached to the BLDC motor strikes on glass surface.

although I'm using a 24v battery, some time if bot got stuck anywhere it used to draw high current of 10A.

Regards:

Soonu Verma