ESD protection for SWD

[Deimantas]

Hi,

Need ESD protection recommendation for NRF51822. While testing nrf51822, we noticed that when SWDCLK gets static dicharge over 900 V, nrf51822 reboots and current consumption increases to ~1.2 mA or only current consumption increases to ~1.2 mA. Found out that in such case, nrf51822, goes to debug mode, and thats why current consumption increases.

Is there any way to detect from application that nRF51822 is in debug mode? Or maybe there is other way to solve this? 470ohm resistor to ground on SWDCLK doesn't help. Nnly helps when SWDCLK connected to ground directly or with 0R resistor, but then we can't program nrf51822.

[AmbystomaLabs]

Seems like if you set approtect the device shouldn’t go into swd mode.

But if you have already tried that then next choice would be a large cap that the cmos can still drive for swd programming. 

There could also be SIDACTors or some other small zener/ schottky solution that may work.

A big inductance and a cap to form a lowpass network could work and still pass the SWD signal.

I've put all kinds of crazy things on 100base-t connections on products to pass ESD and still had solid Ethernet connections. SWD is so slow it should be trivial to solve it.