IMX6SDLCEC datasheet(28/169 Pages) NXP

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i.MX 6Solo/6DualLite Applications Processors for Consumer Products, Rev. 9, 11/2018

NXP Semiconductors

Electrical Characteristics

4.1.4

External Clock Sources

Each i.MX 6Solo/6DualLite processor has two external input system clocks: a low frequency

(RTC_XTALI) and a high frequency (XTALI).

The RTC_XTALI is used for low-frequency functions. It supplies the clock for wake-up circuit,

power-down real time clock operation, and slow system and watch-dog counters. The clock input can be

connected to either external oscillator or a crystal using internal oscillator amplifier. Additionally, there is

an internal ring oscillator, which can be used instead of the RTC_XTALI if accuracy is not important.

NOTE

The internal RTC oscillator does not provide an accurate frequency and is

affected by process, voltage, and temperature variations. NXP strongly

recommends using an external crystal as the RTC_XTALI reference. If the

internal oscillator is used instead, careful consideration must be given to the

timing implications on all of the SoC modules dependent on this clock.

The system clock input XTALI is used to generate the main system clock. It supplies the PLLs and other

peripherals. The system clock input can be connected to either external oscillator or a crystal using internal

oscillator amplifier.

Table 9 shows the interface frequency requirements.

The typical values shown in Table 9 are required for use with NXP BSPs to ensure precise time keeping

and USB operation. For XTALOSC_RTC_XTALI operation, two clock sources are available.

•

On-chip 40 kHz ring oscillator—this clock source has the following characteristics:

— Approximately 25 µA more Idd than crystal oscillator

— Approximately ±50% tolerance

— No external component required

— Starts up quicker than 32 kHz crystal oscillator

•

External crystal oscillator with on-chip support circuit:

— At power up, ring oscillator is utilized. After crystal oscillator is stable, the clock circuit

switches over to the crystal oscillator automatically.

— Higher accuracy than ring oscillator

— If no external crystal is present, then the ring oscillator is used

Table 9. External Input Clock Frequency

Parameter Description

Symbol

Min

Typ

Max

Unit

RTC_XTALI Oscillator1,2

1 External oscillator or a crystal with internal oscillator amplifier.

2 The required frequency stability of this clock source is application dependent. For recommendations, see the Hardware

Development Guide for i.MX 6Dual, 6Quad, 6Solo, 6DualLite Families of Applications Processors (IMX6DQ6SDLHDG).

fckil

—

32.7683/32.0

3 Recommended nominal frequency 32.768 kHz.

—kHz

XTALI Oscillator2,4

4 External oscillator or a fundamental frequency crystal with internal oscillator amplifier.

fxtal

—24

—

MHz

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