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.

[Asbjørn]

You could tie the pin directly to ground on the final product. During development you could have a different implementation/component that would allow you to program the chip. That would allow you to develop normally and also replace the component to ground if you feel that is necessary for the application.

[Simon Third]

Hi Locky, we use the standard J-Link programmers. Mainly because I found that the J-link Lite programmers give programming issues when the VCC of the design is less than 3V. I would also assume that the line drivers in the full spec J-link are better. Have a look at the lines on the scope and compair with the result after changing to 100pF. You only need the cap on the SWDIO/RESET pin.