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ZHCSLA7C December 2019 – September 2023 AM6526 , AM6528 , AM6546 , AM6548

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机械数据 (封装 | 引脚)

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6.9.4.1.1 WKUP_OSC0 Internal Oscillator Clock Source

Figure 6-15 shows the recommended crystal circuit. It is recommended that preproduction printed-circuit board (PCB) designs include the two optional resistors R_bias and R_d in case they are required for proper oscillator operation when combined with production crystal circuit components. In most cases, R_bias is not required and R_d is a 0-Ω resistor. These resistors may be removed from production PCB designs after evaluating oscillator performance with production crystal circuit components installed on preproduction PCBs.

Figure 6-15 WKUP_OSC0 Crystal Implementation

Note:

The load capacitors, C_f1 and C_f2 in the load capacitance equation (1) below, should be chosen such that the below equation is satisfied. C_L 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 associated oscillator WKUP_OSC0_XI, WKUP_OSC0_XO, and VSS pins.

Equation 1.

The crystal must be in the fundamental mode of operation and parallel resonant. Table 6-14 summarizes the required electrical constraints.

Table 6-14 WKUP_OSC0 Crystal Electrical Characteristics

NAME	DESCRIPTION			MIN	TYP	MAX	UNIT
f_p	Parallel resonance crystal frequency			19.2, 20, 24, 25, 26, 27			MHz
C_f1	C_f1 load capacitance for crystal parallel resonance with C_f1 = C_f2			12		24	pF
C_f2	C_f2 load capacitance for crystal parallel resonance with C_f1 = C_f2			12		24	pF
ESR(C_f1,C_f2)	Crystal ESR					100	Ω
C_O	Crystal shunt capacitance	ESR = 30 Ω ESR = 40 Ω	19.2 MHz, 20 MHz, 24 MHz, 25 MHz, 26 MHz, 27 MHz			7	pF
		ESR = 50 Ω	19.2 MHz, 20 MHz			7	pF
		ESR = 50 Ω	24 MHz, 25 MHz, 26 MHz, 27 MHz			5	pF
		ESR = 60 Ω	19.2 MHz, 20 MHz			7	pF
		ESR = 60 Ω	24 MHz, 25 MHz, 26 MHz, 27 MHz	Not Supported			-
		ESR = 80 Ω	19.2 MHz, 20 MHz			5	pF
		ESR = 80 Ω	24 MHz, 25 MHz, 26 MHz, 27 MHz	Not Supported			-
		ESR = 100 Ω	19.2 MHz, 20 MHz			3	pF
		ESR = 100 Ω	24 MHz, 25 MHz, 26 MHz, 27 MHz	Not Supported			-
L_M	Crystal motional inductance for f_p = 20 MHz				10.16		mH
C_M	Crystal motional capacitance				3.42		fF
f_{j(WKUP_OSC0_XI)}	Frequency accuracy, WKUP_OSC0_XI		Ethernet RGMII and RMII not used			±100	ppm
f_{j(WKUP_OSC0_XI)}	Frequency accuracy, WKUP_OSC0_XI		Ethernet RGMII and RMII using derived clock			±50	ppm

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 6-15 details the switching characteristics of the oscillator and the requirements of the input clock.

Table 6-15 WKUP_OSC0 Switching Characteristics – Crystal Mode

NAME	DESCRIPTION	MIN	TYP	MAX	UNIT
f_p	Oscillation frequency	19.2, 20, 24, 25, 26, 27			MHz
t_sX	Start-up time			2^⁽¹⁾	ms

(1) In order to meet the start-up time defined in this table, the crystal needs to be selected according to the following equation:
T_su = K×L_m/ (R_o-ESR) + Δt
where L_m is crystal motional inductance, R_O 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.

Figure 6-16 WKUP_OSC0 Start-up Time