nrf52840 high current (about 2.5uA) while idle

[Kenneth]

I'm developing a beacon-like product using an nrf52840 with S140 on CR2032 battery.  In PS under sleep current draw, it list 0.97uA for system ON, RAM retention OFF.  I'm trying to get this number using BMD-340 evaluation board, but unable to get the current as low as 0.97uA.

I'm running ble_app_uart_pca10056_s140 with RAM disabled through 

    sd_power_ram_power_clr(3, 0x03);
    sd_power_ram_power_clr(4, 0x03);
    sd_power_ram_power_clr(5, 0x03);
    sd_power_ram_power_clr(6, 0x03);
    sd_power_ram_power_clr(7, 0x03);
    sd_power_ram_power_clr(8, 0x0F);

Even with all unused RAM disabled, the current only get down to 1.9uA.  I'm not sure if I'm missing something.  

Any suggestions would be appreciated.

[Sigurd]

Hi,

I'm not sure if I'm missing something. 

 The Softdevice requires the LF clock(internal LFRC run current will be higher than LFXO clock source) + RTC0 to be running.

[Kenneth]

Hi Sigurd,

I'm using external crystal for LF clock.  It should only add 0.23uA.  Even with 1.9uA - 0.23uA, it still doesn't get as low as 0.97.

Do RTC0 draw more current than 0.23uA when it's running as well?

[Sigurd]

I think RTC itself should be around 0.1µA. Then I believe you have RAM retention for the RAM the SoftDevice uses as well.