IMXRT1024IEC datasheet(21/90 Pages) NXP

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Electrical characteristics

i.MX RT1024 Crossover Processors Data Sheet for Industrial Products, Rev. 0, 11/2020

NXP Semiconductors

4.1.4

External clock sources

Each i.MX RT1024 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.

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 12 shows the interface frequency requirements.

The typical values shown in Table 12 are required for use with NXP SDK to ensure precise time keeping

and USB operation. For 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 utilized

The decision of choosing a clock source should be taken based on real-time clock use and precision

time-out.

3 In setting VDD_SNVS_IN voltage with regards to Charging Currents and RTC, refer to the i.MX RT1024 Hardware

Development Guide (IMXRT1024HDG).

Table 12. 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 RT1024 Crossover Processors (IMXRT1024HDG).

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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