JAJSFW1E June 2017 – March 2019 66AK2G12
PRODUCTION DATA.
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Figure 5-9 shows the recommended crystal circuit. It is recommended that preproduction printed-circuit board (PCB) designs include the optional resistor Rd in case a damping resistor is required for proper oscillator operation when combined with production crystal circuit components. In most cases, Rd is a 0-Ω resistor. This resistor may be removed from production PCB designs after evaluating oscillator performance with production crystal circuit components installed on preproduction PCBs.
The SYSOSC_IN terminal has a 400-Ω to 2-kΩ internal pull-down resistor which is enabled when SYSOSC is disabled. This internal resistor prevents the SYSOSC_IN terminal from floating to an invalid logic level which may increase leakage current through the oscillator input buffer.
NOTE
The load capacitors, Cf1 and Cf2 in Figure 5-9, should be chosen such that the below equation is satisfied. CL in the equation is the load specified by the crystal manufacturer. All discrete components used to implement the oscillator circuit should be placed as close as possible to the SYSOSC_IN and SYSOSC_OUT pins.
When selecting a crystal, the system designer must consider the temperature and aging characteristics of a crystal based on the worst case environment and life expectancy of the system.
The crystal must be in the fundamental mode of operation and parallel resonant. Table 5-16 summarizes the required electrical constraints.
NAME | DESCRIPTION | MIN | TYP | MAX | UNIT | ||
---|---|---|---|---|---|---|---|
fc | Parallel resonance crystal frequency | 19.2, 24, 25, 26 | MHz | ||||
Cf1 | Cf1 load capacitance for crystal parallel resonance with Cf1 = Cf2 | 12 | 24 | pF | |||
Cf2 | Cf2 load capacitance for crystal parallel resonance with Cf1 = Cf2 | 12 | 24 | pF | |||
ESR(Cf1, Cf2) | Crystal ESR | 65 | Ω | ||||
CO | Crystal shunt capacitance | 4 | pF | ||||
fa(SYSOSC_IN) | Frequency accuracy(1), SYSOSC_IN | 50 | ppm |