nrf52 high current after sd_power_system_off

[yaron]

Hi I am trying to put the nrf52 device to system off state, in order to get minimal current consumption. When I don't use the soft device, and enter system off state by "NRF_POWER->SYSTEMOFF = 1", I see that CPU current goes down to a few uA. But when I enable the softdevice (using "SOFTDEVICE_HANDLER_INIT"), and than enter system off state by ""softdevice_handler_sd_disable" & "sd_power_system_off", I see CPU current of 5.83 mA!!!. If I add "NRF_POWER->SYSTEMOFF = 1" after "sd_power_system_off" , the CPU current goes down to 2.46 mA. I am currently using soft device version s132_nrf52_1.0.0-3.alpha. Is this a known issue with this version? If not, can some please explain? What is the correct way to enter system off state after soft device is enabled?

Thanks Yaron

[Stefan Birnir Sverrisson]

Hi Yaron

If you are using preview kit, the errata #16 for Eng A chip. Anyways, the s132_nrf52_1.0.0-3.alpha softdevice implements the first line of code described in the anomaly workaround, not allowing low power state on RAM blocks.

Anomaly #16 is fixed in Eng B nRF52, residing on PCA10040 v0.9.0 board.

I have verified the current consumption of system_off by running the ble_app_template example application in nRF52 SDK 0.9.2, running on top of s132_nrf52_1.0.0-3.alpha softdevice, and the current consumption is as expected. The example will enter system off on advertising timeout after 180 seconds, but you can make it timeout after 6 seconds by changing the following timeout at the top of the main file

#define APP_ADV_TIMEOUT_IN_SECONDS      6

Then wake up from system_off by pressing button_1 on the nRF52-DK preview kit. So if you have the preview kit you can check how system_off is entered in this example.

[yaron]

Hi Stefan Thanks for your answer. I am using chip rev B (QFAABA / 1542AB), both on my own hardware, and on the Preview nRF52-DK, and I can't redproduce your results. I have run the ble_app_template, and when the device enters system off state, I measure 2.03 mA!!! (before that, during device advertizing, I measured 500-750uA). Any ideas? Thanks Yaron