NRF9160-SIBA-R datasheet(55/400 Pages) NORDIC

55 / 400 page

Power and clock management

As illustrated in Clock and oscillator setup on page 54, the system supports the following low

frequency clock sources:

• LFRC: 32.768 kHz RC oscillator

• LFXO: 32.768 kHz high accuracy oscillator

The LFCLK clock controller and all LFCLK clock sources are always switched off when in System OFF mode.

The LFCLK clock is started by first selecting the preferred clock source in the LFCLKSRC on page 77

since the LFRC has a large frequency variation.

Note: The LTE modem requires using LFXO as the LFCLK source.

Switching between LFCLK clock sources can be done without stopping the LFCLK clock. A LFCLK clock

source which is running prior to triggering the LFCLKSTART task will continue to run until the selected clock

source has been available. After that the clock sources will be switched. Switching between clock sources

will never introduce a glitch but it will stretch a clock pulse by 0.5 to 1.0 clock cycle (i.e. will delay rising

edge by 0.5 to 1.0 clock cycle).

Note: If the watchdog timer (WDT) is running, the default LFCLK clock source (LFRC - see LFCLKSRC

on page 77) is started automatically (LFCLKSTART task doesn't have to be triggered).

A LFCLKSTARTED event will be generated when the selected LFCLK clock source has started.

Note: When selecting LFXO as clock source for the first time, LFRC quality is provided until LFXO is

stable.

A LFCLKSTOP task will stop global requesting of the LFCLK clock. However, if any system component

(e.g. WDT, modem) requires the LFCLK, the clock won't be stopped. The LFCLKSTOP task should only be

triggered after the STATE field in the LFCLKSTAT register indicates a LFCLK running-state.

5.1.4.2.1 32.768 kHz RC oscillator (LFRC)

The default source of the low frequency clock (LFCLK) is the 32.768 kHz RC oscillator (LFRC).

The LFRC frequency will be affected by variation in temperature.

5.1.4.3 Registers

5.1.4.4 Electrical specification

5.1.4.4.1 64 MHz internal oscillator (HFINT)

Symbol

Description

Min.

Typ.

Max.

Units

fNOM_HFINT

Nominal output frequency

MHz

fTOL_HFINT

Frequency tolerance

+-1

+-5

tSTART_HFINT

Startup time

3.2

µs

5.1.4.4.2 64 MHz high accuracy oscillator (HFXO)

Symbol

Description

Min.

Typ.

Max.

Units

fNOM_HFXO

Nominal output frequency

MHz

fTOL_HFXO

Frequency tolerance

+-1

ppm

tSTART_HFXO

Startup time

TBA

4418_1315 v2.0

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