nRF51 Dk damaged

[Bimal]

Hi,

I have my custom nRF51822 board, and i used to flash the firmware through nRF51 DK kit. As there are two ports through which we can load external boards i was using P20 connector as its mating connector is easy to get. Suddenly i found that while i was working with software part and custom board and nRF51822 where connected with P20 connector. It damaged my custom board SoC(nRF51822) and MCU of nRF51 DK board.

Can you please help me out for following quires/Observations:

• Now i am seeing that P20 SWDIO and SWDCLK are shorted with Ground of nRF51 DK.
• Also 3.3V(VDD) and GND are showing me shorted, so i guess MCU has damaged.
• It also shorted my custom board 3.3V and GND, show i replaced SOC(nRF51822) and now its working fine individually.
• Please tell me is there any protection required on SWD interface.
• Is there any specific reason for this damage.

Need your feedback, As this is stoping me from further process.

[Bimal]

--On External board we have nRF51822 SoC, --Power supply section which converts 24VDC to 5.1VDC through Zener Diode and Further LDO which converts 5.1VDC to 3.3VDC. --Other Optoisolators which are used to isolate UART interface of my external board with my apploication Device. --Which has no such complexity so i wanted to know the route cause of this damage.

--IS there any need to operate my external board at 3V rather than 3.3V. Or do i need to add series resistors at SDIO and SDCLK pins?