34.12.1 Crystal Oscillator (XOSC) Characteristics

Digital Clock Characteristics

The following table describes the oscillator characteristics when a digital clock is applied on XIN.

Table 34-33. Digital Clock Characteristics
Symbol Parameter Conditions Min. Typ. Max. Units
fCPXIN XIN clock frequency Digital mode - - 32 MHz

Crystal Oscillator Characteristics

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

Load Capacitance Equation

CLOAD = ([CXIN + CLEXT] * [CXOUT + CLEXT]) / ([CXIN + CLEXT + CLEXT + CXOUT]) + CSTRAY

Where:

CLOAD = Crystal Mfg. CLOAD specification

CXIN = XOSC XIN pin data sheet specification

CXOUT = XOSC XOUT pin data sheet specification

CLEXT = Required external crystal load capacitor

CSTRAY (Osc PCB capacitance) = 1.5 pF per 12.5 mm (0.5 inches) (TRACE W = 0.175 mm, H = 36 μm, T = 113 μm)

For CXIN and CXOUT within 4 pF of each other, assume CXIN ~= CXOUT ~= CXTAL_EFF = ((CXIN+CXOUT) / 2) (Averaging CXIN and CXOUT will effect final calculated CLOAD value by less than 0.25 pF.)

The load capacitance equation can then be simplified as follows:

CLEXT = 2*CLOAD - CXTAL_EFF - 2*CSTRAY

Table 34-34. Crystal Oscillator Characteristics
Symbol Parameter Conditions Min. Typ. Max. Units
fOUT Crystal oscillator frequency - 0.4 - 32 MHz
ESR Crystal Equivalent Series Resistance
Safety Factor = 3

The AGC doesn’t have any noticeable impact on these measurements.

 f = 0.455 MHz, CL = 100 pF
, XOSC.GAIN = 0 - - 5.6K Ω
f = 2 MHz, CL = 20 pF,
 XOSC.GAIN = 0 - - 330
f = 4 MHz, CL = 20 pF
, XOSC.GAIN = 1 - - 240
f = 8 MHz, CL = 20 pF
, XOSC.GAIN = 2 - - 105
f = 16 MHz, CL = 20 pF
,XOSC.GAIN = 3 - - 60
f = 32 MHz, CL = 18 pF
,XOSC.GAIN = 4 - - 55
CXIN Parasitic capacitor load - - 5.9 - pF
CXOUT Parasitic capacitor load - 3.2 - pF
Current Consumption f = 2 MHz, CL = 20 pF, XOSC.GAIN = 0, AGC off - 65 240 μA
f = 2 MHz, CL = 20 pF, XOSC.GAIN = 0, AGC on - 52 240
f = 4 MHz, CL = 20 pF, XOSC.GAIN = 1, AGC off - 117 309
f = 4 MHz, CL = 20 pF, XOSC.GAIN = 1, AGC on - 74 281
f = 8 MHz, CL = 20 pF, XOSC.GAIN = 2, AGC off - 226 435
f = 8 MHz, CL = 20 pF, XOSC.GAIN = 2, AGC on - 128 356
f = 16 MHz, CL = 20 pF, XOSC.GAIN = 3, AGC off - 502 748
f = 16MHz, CL = 20 pF, XOSC.GAIN = 3, AGC on - 307 627
f = 32 MHz, CL = 18 pF, XOSC.GAIN = 4, AGC off - 1622 2344
f = 32 MHz, CL = 18pF, XOSC.GAIN = 4, AGC on - 615 1422
tSTARTUP Startup time f = 2 MHz, CL = 20 pF,
XOSC.GAIN = 0, ESR = 600Ω - 15.6K 51.0K cycles
f = 4MHz, CL = 20 pF,
XOSC.GAIN = 1, ESR = 100Ω - 6.3K 20.1K
f = 8 MHz, CL = 20 pF,
XOSC.GAIN = 2, ESR = 35Ω - 6.2K 20.3K
f = 16 MHz, CL = 20 pF,
XOSC.GAIN = 3, ESR = 25Ω - 7.7K 21.2K
f = 32 MHz, CL = 18 pF,
XOSC.GAIN = 4, ESR = 40Ω - 6.0K 14.2K
Figure 34-6. Oscillator Connection