Datasheet

Electrical Characteristics
i.MX 6Dual/6Quad Automotive and Infotainment Applications Processors, Rev. 6, 11/2018
NXP Semiconductors 25
4.1.4 External Clock Sources
Each i.MX 6Dual/6Quad 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 watchdog counters. The clock input can be
connected to either an external oscillator or a crystal using the internal oscillator amplifier. Additionally,
there is an internal ring oscillator, that can be used instead of RTC_XTALI when 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 the
internal oscillator amplifier.
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 should be given to
the timing implications on all of the SoC modules dependent on this clock.
Table 7 shows the interface frequency requirements.
The typical values shown in Table 7 are required for use with NXP BSPs 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
10
All digital I/O supplies (NVCC_xxxx) must be powered under normal conditions whether the associated I/O pins are in use or
not, and associated I/O pins need to have a pull-up or pull-down resistor applied to limit any floating gate current.
11
This supply also powers the pre-drivers of the DDR I/O pins; therefore, it must always be provided, even when LVDS is not used.
Table 7. External Input Clock Frequency
Parameter Description Symbol Min Typ Max Unit
RTC_XTALI Oscillator
1,2
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).
f
ckil
— 32.768
3
/32.0
3
Recommended nominal frequency 32.768 kHz.
—kHz
XTALI Oscillator
2,4
4
External oscillator or a fundamental frequency crystal with internal oscillator amplifier.
f
xtal
—24—MHz