What happens to nRF51822 if GPIO is set to source less current than required?

[Elias]

I have a board with some LEDs that are driven in the same way as with the nRF51 DK board (i.e. there is a resistor in series with the LED and you drive the pin low to turn the LED on). However, the series resistor has a lower value.

The datasheet for the non-Nordic board says that the LED pins must be configured to source 5mA. I didn't know this before I programmed the chip, so my program configured the pin to 0.5mA and tried to drive it low, and now I suspect the chip is fried.

I don't know much about the internal circuitry of a pin's drive strength option, so what happens if I have a pin to try to sink more current than is necessary? Is the current limited, or does the chip fry?

[Jørn]

Hello Elias Simon

There is no current limiting circuitry inside the chip. While sinking more current than the specification states is by no means optimal, it should be capable of doing it at least for a little while. Has the pin or chip failed to function properly after you did this? If it functions as it should, it is highly unlikely it took any damage.

Best regards

Jørn Frøysa

[Elias]

The chip seems to still be programmable. I'm using an nRF51 DK as a debugger and nRFgo Studio tells me whether the target is the nRF51422 (on the DK) or the nRF51822 (on the other board) as expected. Reading the program out also seems to work.

I left the GPIO toggling (on a human-visible scale) for several seconds. I can't toggle any GPIOs or do BLE advertising, even though I've confirmed the programs to work with the nRF51 DK.

[Jørn]

Then it is possible the chip has been damaged. Do you have an additional custom board to test your code? This would eliminate any chance of it being a problem with the board, rather than a damaged chip.

[Elias]

I'm on my third board, but I haven't had the courage to test the possible chip-frying code on it. I think I've discovered a different avenue for my main problem, so now, all I'm wondering is how much of a chip could possibly be damaged if it still interfaces with nRFgo Studio properly.

[Jørn]

The chip is flashed and debugged via the SWCLK and SWDIO pins. If you look at Figure 1. "Block diagram" of the product specification you will see that the SWCLK and SWDIO pins do not share hardware with the GPIO. I suspect the problem might lie somewhere in the "AHB multi layer" which lead out to the GPIO hardware, as this could potentially also affect the radio, as it uses the same bus through DMA to fetch data from RAM to transmit.