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.

[Hung Bui]

@Bimal: It's pretty strange what you exerienced. What do you have on your external board ? Do you have any high voltage source on the external board that may shorted and burn the chips ?

Note that the SWD pins on the P20 or P19 is not connected the SWD pins on the nRF51 chip on the DK. So it's strange that replacing the nRF51 chip on the DK can fix the short between SWD pins on P20 to ground. I's suspecting the Atmel (Segger) chip on the DK is damaged.

Note that even there is VTG pin on the SWD port, you still need to provide the external board with it's power source. The VTG pin on the P20 port is only the input pin to detect the external board's power voltage.

[Bimal]

No, In our board we are generating 3.3Volt from 5.2V Zener diode, and which is very stable output +-<80mV.

Also i think you get it wrong, While flashing the external board it damaged the external board and the Atmel Segger chip on Development kit(nRF51-DK). Is that Atmel Segger is very sensitive to this and do we need to put any protection on custom external board in any of the pin like.

1. VCC=3.3V pin,
2. GND pin,
3. SWDIO pin,
4. SWDCLK pin

Please share your feedback for the same.

[Hung Bui]

@Bimal: You are right, I was misunderstood that you replaced the nRF51 chip on the DK board.

No, by design you shouldn't need any further protection on those pins. We actually haven't heard of any report on the issue with the external SWD on the DK that can cause the damage to external chip or the Segger chip.

What else do you have on the external board beside the passive components and the nRF51 chip ?

[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?

[Hung Bui]

• No, it's should be fine to run your board at 3V. It's also 3V on the nRF51 chip on the DK. I don't think you need to add any series resistors on SDIO and SDCLK. I think if you can make sure there is no short between the 24VDC to the board circuit, you should be fine.