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

Stian Røed Hafskjold — Tue, 27 Jul 2021 12:42:30 GMT

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.

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

Stian Røed Hafskjold — Fri, 23 Jul 2021 14:24:42 GMT

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

[quote user=""]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" ?[/quote]

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.