nRF9160 Serial LTE modem #XSLEEP=2 with CONFIG_SLM_EXTERNAL_XTAL=y ~1mA in PSM

[Michal Mühlpachr]

Hi,

nRF9160 in nRF9160DK with NCS v1.6.0 and master, power consumption measured by PPK2.

With CONFIG_SLM_EXTERNAL_XTAL=n nRF9160 average power consumption is ~7uA after #XSLEEP=2 in PSM.

With CONFIG_SLM_EXTERNAL_XTAL=y nRF9160 average power consumption is ~1040uA after #XSLEEP=2 in PSM (alike with #XSLEEP=1).

It seams that nRF9160 High frequency clock keeps running after #XSLEEP=2 with CONFIG_SLM_EXTERNAL_XTAL=y.

Can you check it an implement power savings during #XSLEEP=2 and #XSLEEP=1 with CONFIG_SLM_EXTERNAL_XTAL=y please ?

Why is in SLM CONFIG_SLM_EXTERNAL_XTAL=n if we consider UART device documentation "The external crystal oscillator must be enabled to obtain sufficient clock accuracy for stable communication" ?

devzone.nordicsemi.com/.../safe-temperature-range-for-nrf52840---nrf9160-uart-115200-without-external-crystals-for-hf-clocks

[Stian Røed Hafskjold]

Hi, it sounds link the HF crystal is not turned off after XSLEEP=2. I asked the developer to look into this. Will update you soon

 

Why is in SLM CONFIG_SLM_EXTERNAL_XTAL=n if we consider UART device documentation "The external crystal oscillator must be enabled to obtain sufficient clock accuracy for stable communication" ?

 Here is the clock accuracy specification: https://infocenter.nordicsemi.com/topic/ps_nrf9160/pmu_oscillators.html?cp=2_0_0_4_0_3_3_0#unique_1249010512

The HFINT can have a maximum of 5% drift. This may not be good enough for UART communication. Usually it goes fine. But for critical communication, unless some sort of error checking is implemented, the HFXO should be used.

[Stian Røed Hafskjold]

The developer has been notified of this high current consumption, and will update the application to turn off the HF crystal after UART is turned off using XSLEEP=2. Testing shows that the sleep current will be the same with or without the CONFIG_SLM_EXTERNAL_XTAL flag. The application will be updated soon.