[26] CLOCK,LFXO: System locks up when set in System ON IDLE while waiting for EVENTS_LFCLKSTARTED

This anomaly applies to IC Rev. Revision 1, build codes SICA-B0A.

It was inherited from the previous IC revision Engineering A.

Symptoms

LFCLOCK is not precise after reset until LFXO is available.

Conditions

The LFXO is enabled and EVENTS_LFCLKSTARTED not received yet.

Consequences

Imprecise LFCLOCK may lead to system lockup while waiting for the LFXO to become available.

Workaround

Do not enter System ON IDLE in the period between writing TASK_LFCLKSTART= 1 and receiving EVENTS_ LFCLKSTARTED. The startup time for the LFXO is stated in the electrical parameter tSTART_LFXO in 32.768 kHz high accuracy oscillator (LFXO) in nRF9160 Product Specification.
Note: The LTE modem requires LFXO as LFCLK source.