I am using sd_power_system_off() to enter System Off. It is my understanding that all peripherals are off in System Off, but that GPIO configuration is retained. I have a board that should, and has, gone down to 33uA at the battery when powered down, 0.6uA of which should be from the Nordic chip in its System Off mode.
Previous boards had a Rev1 Nordic nRF51822, and were using soft device 6.0.0. These achieved the expected 33 uA in low power mode. A new set of boards were made with Rev3 Nordic chips, nRF51822 QFACA00 (0x0087), and are using soft device 8.0.0.
These new set of boards only drop down to 70uA - 100uA in low power. What was found is that if the Nordic's UART Rx signal is pulled to ground with a 1M resistor at this point, that the power drain drops to the expected 33uA.
This is what has prompted my question. Is there some GPIO configuration that I should be doing in addition to (before calling) sd_power_system_off()? For my controller MCU (a Cortex M3), am am using a "Stop" mode for which I make sure to configure all GPIOs as Analog Inputs. I am not currently doing anything for the Nordic chip except the System Off call.
