45.12.1.2 Crystal Oscillator Characteristics

The following table describes the characteristics for the oscillator when a crystal is connected between XIN and XOUT as shown in Figure 45-5. The user must choose a crystal oscillator where the crystal load capacitance C_Lis within the range given in the table. The exact value of C_L can be found in the crystal data sheet. The capacitance of the external capacitors (C_LEXT) can then be computed as follows:

C_LOAD = { ( [C_XIN + C_LEXT] * [C_XOUT + C_LEXT] ) / [C_XIN + C_LEXT + C_LEXT + C_XOUT] } + C_STRAY.

Where CSTRAY is the capacitance of the PCB.

For C_XIN ≠ C_XOUT, but with a difference smaller than 4pF, we can consider C_XIN ≈ C_XOUT ≈ C_Xeff = ( C_XIN + C_XOUT) / 2.

This results in a simplified formula for computing C_LEXT, as follows:

C_LEXT = 2*CL - 2*C_STRAY - C_Xeff

Table 45-47. Multi Crystal Oscillator Electrical Characteristics ⁽¹⁾
Symbol	Parameter	Conditions	Min.	Typ.	Max	Units
Fout	Crystal oscillator frequency		0.4	-	32	MHz
CL	Crystal Load	F = 0.455 MHz	-	-	100	pF
		F = 2 MHz	-	-	20
		F = 4 MHz	-	-	20
		F = 8 MHz	-	-	20
		F = 16 MHz	-	-	20
		F = 32 MHz	-	-	18
ESR	Crystal Equivalent Series Resistance - SF = 3	F = 0.455 MHz CL = 100pF XOSC.GAIN = 0	-	-	443	Ω
		F = 2MHz CL=20pF XOSC.GAIN=0	-	-	383
		F = 4MHz CL=20pF XOSC.GAIN=1	-	-	218
		F = 8MHz CL=20pF XOSC.GAIN=2	-	-	114
		F = 16MHz CL=20pF XOSC.GAIN=3	-	-	61
		F = 32MHz CL=18pF XOSC.GAIN=4	-	-	41
Cxin	Parasitic load capacitor		-	5.9	-	pF
Cxout	Parasitic load capacitor		-	3.1	-	pF
Tstart	Startup time	F = 2MHz CL=20pF XOSC.GAIN=0	-	12.3	35.3	KCycles
		F = 4MHz CL=20pF XOSC.GAIN=1	-	8.2	21.4
		F = 8MHz CL=20pF XOSC.GAIN=2	-	6.2	14.3
		F = 16MHz CL=20pF XOSC.GAIN=3	-	10.8	18.1
		F = 32MHz CL=18pF XOSC.GAIN=4	-	8.7	15.4

These are based on characterization.

Table 45-48. Power Consumption ⁽¹⁾
Symbol	Parameters	Conditions	Ta	Typ.	Max	Units
IDD	Current consumption	F = 2MHz CL=20pF XOSC.GAIN=0 VDD = 5.0V AGC=OFF	Max 85°C Typ 25°C	150	202	µA
		AGC=ON		138	192
		F = 4MHz CL=20pF XOSC.GAIN=1 VDD = 5.0V AGC=OFF		220	288
		AGC=ON		175	260
		F = 8MHz CL=20pF XOSC.GAIN=2 VDD = 5.0V AGC=OFF		350	416
		AGC=ON		247	321
		F = 16MHz CL=20pF XOSC.GAIN=3 VDD = 5.0V AGC=OFF		663	843
		AGC=ON		429	699
		F = 32MHz CL=18pF XOSC.GAIN=4 VDD = 5.0V AGC=OFF		1975	2329
		AGC=ON		874	1181