46.11 XOSC Electrical Specifications

Table 46-13. External Crystal Oscillator and Clock Electrical Specifications ⁽¹⁾
AC CHARACTERISTICS			Standard Operating Conditions: VDD and VDDIO 2.7V to 5.5V (unless otherwise stated) Operating temperature: -40°C ≤ T_A ≤ +85°C for Industrial
Param. No.	Symbol	Characteristics	Min.	Typ.	Max.	Units	Conditions
XOSC_1	F_OSC_XOSC	XOSC Crystal Frequency	0.4	—	32	MHz	XOSCCTRLn.XTALEN=1 XIN, XOUT Primary Osc
XOSC_1A	T_OSC	T_OSC= 1/F_OSC_XOSC	31.25	—	2500	ns	See parameter XOSC_1 for F_OSC_XOSC value
XOSC_2	XOSC_ST ^(1,2)	XOSC Crystal Stabilization Time	—	12300	⁽³⁾	T_OSC	Crystal stabilization time only, not Oscillator Ready. CL = 20pF, XOSC.GAIN = 0,1,2,3,4
XOSC_3	C_XIN	XOSC XIN parasitic pin capacitance	—	5.9	—	pF	—
XOSC_5	C_XOUT	XOSC XOUT parasitic pin capacitance	—	3.1	—	pF	—
XOSC_11	C_LOAD⁽²⁾	XOSC Crystal FOSC = 0.455 MHz	—	—	100	pF	—
XOSC_13		XOSC Crystal FOSC = 2 MHz	—	—	20	pF	—
XOSC_15		XOSC Crystal FOSC = 4 MHz	—	—	20	pF	—
XOSC_17		XOSC Crystal FOSC = 8 MHz	—	—	20	pF	—
XOSC_19		XOSC Crystal FOSC = 16 MHz	—	—	20	pF	—
XOSC_20		XOSC Crystal FOSC = 32 MHz	—	—	12	pF	—
XOSC_21	ESR	XOSC Crystal FOSC = 0.455 MHz	—	—	443	Ω	CL = 100pF, XOSC.GAIN = 0
XOSC_23		XOSC Crystal FOSC = 2 MHz	—	—	383	Ω	CL = 20pF, XOSC.GAIN = 0
XOSC_25		XOSC Crystal FOSC = 4 MHz	—	—	218	Ω	CL = 20pF, XOSC.GAIN = 1
XOSC_27		XOSC Crystal FOSC = 8 MHz	—	—	114	Ω	CL = 20pF, XOSC.GAIN = 2
XOSC_29		XOSC Crystal FOSC = 16 MHz	—	—	58	Ω	CL = 20pF, XOSC.GAIN = 3
XOSC_29		XOSC Crystal FOSC = 32 MHz	—	—	62	Ω	CL = 12pF, XOSC.GAIN = 4
XOSC_35	F_OSC_XCLK	Ext Clock Oscillator Input Freq (X_INpin)	0	—	48	MHz	XOSCCTRL.XTALEN=0
XOSC_37	XCLK_DC	Ext Clock Oscillator (X_IN) Duty Cycle	40	50	60	%	XOSCCTRL.XTALEN=0
XOSC_39	XCLK_FST	Primary XIN Clock Fail Safe Time-out Period	—	4*1/(OSC48M_1/2^{^OSCCTRL.CFDPRESC})	—	µs	—

Note:

This is for guidance only. A major component of crystal start-up time is based on the second party crystal MFG parasitics that are outside the scope of this specification. If this is a major concern the customer would need to characterize this based on their design choices.
CRYSTAL LOAD CAPACITOR CALCULATION
GIVEN:
- Standard PCB trace capacitance = 1.5 pF per 12.5 mm (0.5 inches) (i.e. PCB STD TRACE W = 0.175 mm, H = 36 μm, T = 113 μm)
- Xtal PCB capacitance typical therefore ~= 2.5pF for a tight PCB xtal layout
- For CXIN and CXOUT within 4pF of each other, Assume CXTAL_EFF = ((CXIN+CXOUT) / 2)
  Note: Averaging CXIN and CXOUT will effect final calculated CLOAD value by less than 0.25 pF.
EQUATION 1:
MFG C_LOAD Spec = {( [C_XIN + C1] * [C_XOUT + C2] ) / [C_XIN + C1 + C2 + C_XOUT] } + estimated oscillator PCB stray capacitance
- Assuming C1 = C2 and C_XIN ~= C_XOUT, the formula can be further simplified and restated to solve for C1 and C2 by:
EQUATION 2: (Simplified version of equation 1)
C1 = C2 = ((2 * MFG C_LOAD spec) - C_{XTAL_EFF} - (2 * PCB capacitance))
EXAMPLE ONLY:
- XTAL Mfg C_LOAD Data Sheet Spec = 12 pF
- PCB XTAL trace Capacitance = 2.5 pF
- C_XIN pin = 6.5 pF, C_XOUT pin = 4.5 pF. Therefore C_{XTAL_EFF} = ((C_XIN+C_XOUT) / 2)
C_{XTAL_EFF} = ((6.5 + 4.5)/2) = 5.5 pF
C1 = C2 = ((2 * MFG C_LOAD spec) - C_{XTAL_EFF} - (2 * PCB capacitance))
C1 = C2 = (24 - 5.5 - (2 * 2.5))
C1 = C2 = 13.5 pF (Always rounded down)
C1 = C2 = 13 pF (i.e., for hypothetical example crystal external load capacitors)
User C1=C2=13 pF ≤ C_LOAD(max) spec
Figure 46-5. XTAL
User Selectable in OSCCTRL.STARTUP.
Minimum value in order to respect the FDPLL96M minimum input frequency parameter (FDPLL_1). Only applicable when XOSC is used to feed the FDPLL96M.