Is my dev board ( pca10040) broken?

[bryanhsieh]

Hi Everyone,

Recently I have been trying to measure the current consumption from the dev board. I have set up the board as instructed by cutting SB9 and soldering SB11 and SB12. (swapping between external and battery supply). But when I tried to measure current I noticed something odd, if I don't short P22, no power should be delivered to nrf52832 and this is indeed the case. But as soon as I short P22, power flows to nrf52832 and continues to flow even after the shunt jumper has been removed. I can not work out, how the mcu can continue to stay on without the shunt jumper. And how this behavior is triggered only after shorting P22 once. Resetting the chip turns it back to normal.

Measuring P22 reveals that is open circuit when device not powered but when powered and after inserting the shunt once, it becomes a short circuit. Does anyone know why this is happening, ie how can VDD_nrf be shorted to VDD, they seem to be very far away from each other on the pcb layout apart from where they join at SB9 and P22.

Thanks for the help, Bryan

[Sigurd]

Hi,

One explanation to this behavior is that the chip is being powered through the GPIO pins. With the jumper attached, the chip starts up, and when you remove the jumper afterwards, the voltage on the GPIO pins are high enough to keep the chip powered even after you remove the jumper. When you reset the board without the jumper, you don’t have enough power on the GPIO pins to start the chip up.