Datasheet
i.MX 8M Dual / 8M QuadLite / 8M Quad Applications Processors Data Sheet for Industrial Products, Rev. 0, 01/2018
18 NXP Semiconductors
Electrical characteristics
3.1.4 External clock sources
A 25 MHz oscillator is used as the primary clock source for the PLLs to generate the clock for CPU, BUS,
and high-speed interfaces. For fractional PLLs, the 25 MHz clock from the oscillator can be directly used
as the PLL reference clock.
A 27 MHz oscillator is used as the reference clock for HDMI PHY. Also it can be used as the alternative
source for the fractional PLLs.
A 32 kHz clock input pin is used as the RTC clock source. It is expected to be supplied by an external
32.768 kHz oscillator. When an external RTC clock input is not present, the 32 kHz clock for internal logic
is generated by the 25 MHz oscillator. The frequency of the internal 32 kHz clock will be 31.25 kHz.
Two pairs of differential clock inputs, named as CLK1P and CLK1N, can be used as the reference clock
for the PLL. This is mainly used for a high-speed clock input during testing.
Four clock inputs to the CCM from normal GPIO pads via IOMUX can be used as the clock sources in the
CCM.
Table 8 shows the interface frequency requirements.
The typical values shown in Table 8 are required for use with NXP BSPs to ensure precise time keeping
and USB operation. For RTC operation, two clock sources are available.The decision of choosing a clock
source should be made based on real-time clock use and precision timeout.
3.1.5 Maximum supply currents
Table 9 represents the maximum momentary current transients on power lines and should be used for
power supply selection. Maximum currents are higher by far than the average power consumption of
typical use cases.
Table 8. External input clock frequency
Parameter description Symbol Min Typ Max Unit
RTC
1,2
1
External oscillator or a crystal with internal oscillator amplifier.
2
The required frequency stability of this clock source is application dependent.
f
ckil
— 32.768
3
3
Recommended nominal frequency 32.768 kHz.
—kHz
XTALI_25M/XTALO_25M
2
f
xtal
20 25 40 MHz
XTALI_27M/XTALO_27M
2
f
xtal
20 27 40 MHz
Table 9. Maximum supply currents
1
Power rail Max current Unit
VDD_ARM 384 to 2410
1
mA
VDD_SOC 1400 to 1870
1
mA
VDD_GPU 0 to 2040
1
mA