Custom nRF52811 is not running off coin cell battery.

[Evan Knobler]

Hello, I have an nRF52811 on a custom board and have been having some issues. I have a nRF52840DK which I used to flash the custom board (while powering the board with the VDD pin of the DK) with a test program which lights up an LED connected to one of the GPIOs of the chip and this works fine. However, when I try to power the chip with a CR2032, the LED didn't light up, implying the test program wasn't running. I tried hooking up an external power supply to the board, sourcing 3V, but that didn't work either. It seems the only time the program runs is when the chip gets power from the DK. My only guess is that the battery/power supply aren't sourcing enough current to power the chip but I can't imagine why that would happen. I know the connections are good on the custom board because I have another LED, independent from the chip, that lights up when the board gets power.

Another thing that happens is sometimes the program doesn't run even when it gets power from the DK. There are times when I power up the board and and the LED connected to the GPIO doesn't light up and only after power cycling does the program run and light up the LED.

Is there anything I'm doing wrong that can explain why these issues are happening?

Thanks in advance for your help!

[patjshan]

it sounds like the vcc of the chip is not properly connected to whatever is handling power on your board. The DK is likely supplying power to the chip when you have it connected over programming wires. I haven't used the 840 DK for programming but I use the 832DK frequently and I know that there is a chip select solder bridge that must be connected/disconnnected depending on if you would like to program an external board or the onboard chip on the DK. This may explain why you don't always see the LED light up even when you are connected to the DK. 

I would suggest you probe the vcc pins on your custom board while a power supply is connected but without the DK connected. if you don't see enough voltage (I believe you need at least 1.7V to run but I'm not a nordic engineer so check that) the chip will not run. And if there is an issue with your board that you get worked out i would also suggest disconnecting the Vcc supply on the DK from the programming pads and only connecting Vcc target (the reference to the custom boards Vcc, this DOES NOT power the board butrather detects the voltage of the board the programmer is going to talk to) SWIO, SWCLK, and GND Detect (same idea as Vcc target, this is not actually the path for return current but the reference for the programming chip. Doing this has sped up the programming process for me immensely since you can plug in external power to your custom board and program it at the same time, allowing for useful ADC measurements etc. even while in debug mode.   

Again I'm not a nordic engineer though, just been working with the chip for a while and that would be my first guess.