AM6421 datasheet(133/237 Pages) TI

133 / 237 page

AM65x_MCU_OSC_SC_06

Device

MCU_OSC0_XO

MCU_OSC0_XI

PCBXIXO

PCB

Signal Traces

Crystal Circuit

Components

XIXO

Figure 7-18. Shunt Capacitance

A crystal should be chosen such that the below equation is satisfied. CO in the equation is the maximum shunt

capacitance specified by the crystal manufacturer.

Cshunt ≥ CO + CPCBXIXO + CXIXO

For example, the equation would be satisfied when the crystal being used is 25 MHz with an ESR = 30 Ω,

CPCBXIXO = 0.04 pF, CXIXO = 0.01 pF, and shunt capacitance of the crystal is less than or equal to 6.95 pF.

7.10.4.1.2 MCU_OSC0 LVCMOS Digital Clock Source

Figure 7-19 shows the recommended oscillator connections when MCU_OSC0_XI is connected to a 1.8-V

LVCMOS square-wave digital clock source.

Note

A DC steady-state condition is not allowed on MCU_OSC0_XI when the oscillator is powered up. This

is not allowed because MCU_OSC0_XI is internally AC coupled to a comparator that may enter a

unknown state when DC is applied to the input. Therefore, application software should power down

MCU_OSC0 any time MCU_OSC0_XI is not toggling between logic states.

Device

MCU_OSC0_XO

MCU_OSC0_XI

AM65x_MCU_OSC_EXT_CLK_03

PCB Ground

Figure 7-19. 1.8-V LVCMOS-Compatible Clock Input

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SPRSP56 – JANUARY 2021

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AM6421 Datasheet(PDF) 133 Page - Texas Instruments