AN663 데이터 시트보기 (PDF) - Silicon Laboratories

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AN663

PRECISION32 MCU FAMILY CLOCKING OPTIONS

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AN663

2.3. RTC Oscillator (RTCnOSC)

The RTC oscillator is part of the RTC module and is derived from the 32.768 kHz watch crystal or CMOS oscillator.

This oscillator can be a source for the AHB or selected as the RTC timer clock source.

The load capacitance for the watch crystal is internal and adjustable, so no external components other than the

crystal are required. The crystal should be connected directly across the RTC1 and RTC2 pins on the device, and

these pins should be configured for analog input mode.

The RTC oscillator is more accurate than the low frequency oscillator, allowing for precision timekeeping with the

32-bit RTC timer.

Figure 3 shows the block diagram for the low frequency and RTC oscillators.

External CMOS Clock

RTC1

External Crystal

32.768

kHz

RTC1

RTC2

RTC1

RTC2

Load Capacitance

RTC External

Oscillator Control

Low Frequency

Oscillator

Frequency Adjust

RTCn Module

RTCnOSC Clock

RTCnOSC_OUT

Additional RTC

Module

Components

RTC Timer

RTCn_OUT

LFOSCn Clock

Figure 3. Low Frequency and RTC Oscillator Block Diagram

4

Rev. 0.1

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