39.8.1.2 Crystal Oscillator Characteristics

The following table describes the characteristics for the oscillator when a crystal is connected between XIN and XOUT . 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)

Table 39-32. Crystal Oscillator Characteristics (Device Variant A)
SymbolParameterConditionsMin.Typ.Max.Units
fOUTCrystal oscillator frequency0.4-32MHz
ESRCrystal Equivalent Series Resistance
Safety Factor = 3

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

f = 0.455 MHz, CL = 100pF
XOSC.GAIN = 0--5.6KΩ
f = 2MHz, CL = 20pF
XOSC.GAIN = 0--416
f = 4MHz, CL = 20pF
XOSC.GAIN = 1--243
f = 8 MHz, CL = 20pF
XOSC.GAIN = 2--138
f = 16 MHz, CL = 20pF
XOSC.GAIN = 3--66
f = 32MHz, CL = 18pF
XOSC.GAIN = 4--56
CXINParasitic capacitor load-5.9-pF
CXOUTParasitic capacitor load-3.2-pF
Current Consumptionf = 2MHz, CL = 20pF, AGC off276590μA
f = 2MHz, CL = 20pF, AGC on145279
f = 4MHz, CL = 20pF, AGC off61117161
f = 4MHz, CL = 20pF, AGC on2374110
f = 8MHz, CL = 20pF, AGC off131226319
f = 8MHz, CL = 20pF, AGC on56128193
f = 16MHz, CL = 20pF, AGC off305502742
f = 16MHz, CL = 20pF, AGC on116307627
f = 32MHz, CL = 18pF, AGC off103116222344
f = 32MHz, CL = 18pF, AGC on2786151422
tSTARTUPStart-up timef = 2MHz, CL = 20pF,
XOSC.GAIN = 0, ESR = 600Ω-14K48Kcycles
f = 4MHz, CL = 20pF,
XOSC.GAIN = 1, ESR = 100Ω-680019.5K
f = 8 MHz, CL = 20pF,
XOSC.GAIN = 2, ESR = 35Ω-555013K
f = 16 MHz, CL = 20pF,
XOSC.GAIN = 3, ESR = 25Ω-675014.5K
f = 32MHz, CL = 18pF,
XOSC.GAIN = 4, ESR = 40Ω-5.3K9.6K
Table 39-33. Crystal Oscillator Characteristics (Device Variant B, C, D and L)
SymbolParameterConditionsMin.Typ.Max.Units
fOUTCrystal oscillator frequency0.4-32MHz
ESRCrystal Equivalent Series Resistance
Safety Factor = 3

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

f = 0.455 MHz, CL = 100pF
XOSC.GAIN = 0--5.6KΩ
f = 2MHz, CL = 20pF
XOSC.GAIN = 0--416
f = 4MHz, CL = 20pF
XOSC.GAIN = 1--243
f = 8 MHz, CL = 20pF
XOSC.GAIN = 2--138
f = 16 MHz, CL = 20pF
XOSC.GAIN = 3--66
f = 32MHz, CL = 18pF
XOSC.GAIN = 4--56
CXINParasitic capacitor load-5.9-pF
CXOUTParasitic capacitor load-3.2-pF
Current Consumptionf = 2MHz, CL = 20pF, AGC off276590μA
f = 2MHz, CL = 20pF, AGC on145279
f = 4MHz, CL = 20pF, AGC off61117160
f = 4MHz, CL = 20pF, AGC on2374110
f = 8MHz, CL = 20pF, AGC off131226319
f = 8MHz, CL = 20pF, AGC on56128193
f = 16MHz, CL = 20pF, AGC off305502741
f = 16MHz, CL = 20pF, AGC on116307626
f = 32MHz, CL = 18pF, AGC off103116222344
f = 32MHz, CL = 18pF, AGC on2786151400
tSTARTUPStart-up timef = 2MHz, CL = 20pF,
XOSC.GAIN = 0, ESR = 600Ω-14K48Kcycles
f = 4MHz, CL = 20pF,
XOSC.GAIN = 1, ESR = 100Ω-680019.5K
f = 8 MHz, CL = 20pF,
XOSC.GAIN = 2, ESR = 35Ω-555013K
f = 16 MHz, CL = 20pF,
XOSC.GAIN = 3, ESR = 25Ω-675014.5K
f = 32MHz, CL = 18pF,
XOSC.GAIN = 4, ESR = 40Ω-5.3K9.6K
Figure 39-4. Oscillator Connection