IMX7SCEC datasheet(24/152 Pages) NXP

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Electrical characteristics

i.MX 7Solo Family of Applications Processors Datasheet, Rev. 5, 07/2017

NXP Semiconductors

4.1.4

External clock sources

Each i.MX 7Solo 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 resistor-capacitor (RC) 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 an external oscillator or a crystal using

internal oscillator amplifier.

Table 11 shows the interface frequency requirements.

The typical values shown in Table 11 are required for use with NXP BSPs to ensure precise time keeping

and USB operation. For RTC_XTALI operation, two clock sources are available. If there is not an

externally applied oscillator to RTC_XTALI, the internal oscillator takes over.

•

On-chip 32 kHz RC oscillator—this clock source has the following characteristics:

— Approximately 25 µA more IDD than crystal oscillator

— Approximately ±10% tolerance

— No external component required

— Starts up faster than 32 kHz crystal oscillator

— Three configurations for this input:

– External oscillator

– External crystal coupled to RTC_XTALI and RTC_XTALO

VDDA_PHY_1P8

VDDA_MIPI_1P8

Connect directly (short) via board level

1 On-chip LDOs are designed to supply i.MX 7Solo loads and must not be used to supply external loads.

Table 11. 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. See Hardware Development Guide for

i.MX7Dual and 7Solo Applications Processors.

fckil

—32.7683

3 Recommended nominal frequency 32.768 kHz.

—kHz

XTALI Oscillator2,4

4 External oscillator or a fundamental frequency crystal appropriately coupled to the internal oscillator amplifier.

fxtal

MHz

Table 10. On-chip LDOs1 and their on-chip loads(continued)

Voltage Source

Load

Comment

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