AM6548 datasheet(157/284 Pages) TI

157 / 284 page

CL=

C C

(C +C )

SPRS932_CLOCK_03

Figure 7-20. Load Capacitance Equation

The crystal must be in the fundamental mode of operation and parallel resonant. Table 7-18 summarizes the

required electrical constraints.

Table 7-18. OSC1 Crystal Electrical Characteristics

NAME

DESCRIPTION

MIN

TYP

MAX UNIT

Parallel resonance crystal frequency

19.2, 20, 24, 25, 26, 27

MHz

Cf1

Cf1 load capacitance for crystal parallel resonance with Cf1 = Cf2

Cf2

Cf2 load capacitance for crystal parallel resonance with Cf1 = Cf2

ESR(Cf1,Cf2) Crystal ESR

100

Crystal shunt capacitance

ESR = 30 Ω

ESR = 40 Ω

19.2 MHz, 20 MHz, 24 MHz, 25

MHz, 26 MHz, 27 MHz

ESR = 50 Ω

19.2 MHz, 20 MHz

24 MHz, 25 MHz, 26 MHz, 27

MHz

ESR = 60 Ω

19.2 MHz, 20 MHz

24 MHz, 25 MHz, 26 MHz, 27

MHz

Not Supported

ESR = 80 Ω

19.2 MHz, 20 MHz

24 MHz, 25 MHz, 26 MHz, 27

MHz

Not Supported

ESR = 100 Ω

19.2 MHz, 20 MHz

24 MHz, 25 MHz, 26 MHz, 27

MHz

Not Supported

Crystal motional inductance for fp = 20 MHz

10.16

Crystal motional capacitance

3.42

fj(OSC1_XI)

Frequency accuracy, OSC1_XI

Ethernet RGMII and RMII not

used

±100

ppm

Ethernet RGMII and RMII using

derived clock

±50

When selecting a crystal, the system design must consider the temperature and aging characteristics of a based

on the worst case environment and expected life expectancy of the system.

Table 7-19 details the switching characteristics of the oscillator and the requirements of the input clock.

Table 7-19. OSC1 Switching Characteristics – Crystal Mode

NAME

DESCRIPTION

MIN

TYP

MAX

UNIT

Oscillation frequency

19.2, 20, 24, 25, 26, 27

MHz

tsX

Start-up time

2(1)

(1)

In order to meet the start-up time defined in this table, the crystal needs to be selected according to the following equation:

Tsu = K×Lm/ (Ro-ESR) + Δt

where Lm is crystal motional inductance, RO is the negative resistance of amplifier, ESR is the crystal Effective series resistance and K

is a constant which represents the initial conditions. Δt is the time amplifier takes to reach its bias point after power down is released.

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AM6548, AM6528, AM6546, AM6526

SPRSP52B – DECEMBER 2019 – REVISED JUNE 2021

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