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nRF9160-DK power consumption in shut is over 500 uA

Hi,

I am trying to achieve the lowest current consumption possible on the nRF9160-DK, which should be about 1.4 uA in modem shut down state.
Unfortunately, my best result is a shut down current of 525 uA. I am pretty sure that I am entering the shut down mode, because the
current consumption drops from 1.3 mA to 525 uA at the respective runtime.

My Setup:

nRF9160 SICA
MFW 1.2.3

prj.conf:
CONFIG_BSD_LIBRARY=y
CONFIG_BSD_LIBRARY_SYS_INIT=n

CONFIG_NETWORKING=y
CONFIG_NET_SOCKETS=y
CONFIG_NET_SOCKETS_POSIX_NAMES=y
CONFIG_NET_NATIVE=n

CONFIG_HEAP_MEM_POOL_SIZE=8192
CONFIG_MAIN_STACK_SIZE=8192

CONFIG_MODEM_KEY_MGMT=y
CONFIG_LTE_LINK_CONTROL=y
CONFIG_LTE_AUTO_INIT_AND_CONNECT=n

CONFIG_UART_CONSOLE=n
CONFIG_SERIAL=n
CONFIG_LOG=n
CONFIG_BSD_LIBRARY_TRACE_ENABLED=n
CONFIG_STDOUT_CONSOLE=n
CONFIG_CONSOLE=n

Application template: Mqtt simple
main.c:
while(1) {
    k_sleep(K_MSEC(2000));
    if (!IS_ENABLED(CONFIG_AT_HOST_LIBRARY)) {
        // Stop the UART RX for power consumption reasons
        NRF_UARTE0_NS->TASKS_STOPRX = 1;
        NRF_UARTE1_NS->TASKS_STOPRX = 1;
    }
    k_sleep(K_MSEC(2000));
    bsdlib_shutdown();
    k_sleep(K_MSEC(5000));
    NRF_REGULATORS_NS->SYSTEMOFF = 1;
}

I do not initialize any additional periphery. I am running out of ideas on how to decrease the current consumption at this point.
I know that the current consumption shall be far lower, because I managed to measure a PSM floor current of ~ 100 uA on the same DK
a year ago. But right now I don't even use the whole RF-part. So could you please tell me what I could try to decrease the shut-down
current?

And there is another question for my further work: How can I uninitialize or disable a driver, if I used the device_get_binding() funktion?

For example the pwm, adc and i2c driver? I didn't find a function in the respective header files.

Thanks and best regards

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