38.8.1.2 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 38-4. 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)
| 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 = 100pF XOSC.GAIN = 0 | - | - | 5.6K | Ω |
| 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 | |||
| CXIN | Parasitic capacitor load | - | 5.9 | - | pF | |
| CXOUT | Parasitic capacitor load | - | 3.2 | - | pF | |
| IXOSC | Current Consumption | f = 2MHz, CL = 20pF, AGC off | 65 | 87 | μA | |
| f = 2MHz, CL = 20pF, AGC on | 52 | 76 | ||||
| f = 4MHz, CL = 20pF, AGC off | 117 | 155 | ||||
| f = 4MHz, CL = 20pF, AGC on | 74 | 104 | ||||
| f = 8MHz, CL = 20pF, AGC off | 226 | 308 | ||||
| f = 8MHz, CL = 20pF, AGC on | 128 | 180 | ||||
| f = 16MHz, CL = 20pF, AGC off | 502 | 714 | ||||
| f = 16MHz, CL = 20pF, AGC on | 307 | 590 | ||||
| f = 32MHz, CL = 18pF, AGC off | 1622 | 2257 | ||||
| f = 32MHz, CL = 18pF, AGC on | 615 | 1280 | ||||
| tSTARTUP | Startup time | f = 2MHz, CL = 20pF, XOSC.GAIN = 0, ESR = 600Ω | - | 14K | 48K | cycles |
| f = 4MHz, CL = 20pF, XOSC.GAIN = 1, ESR = 100Ω | - | 6800 | 19.5K | |||
| f = 8 MHz, CL = 20pF, XOSC.GAIN = 2, ESR = 35Ω | - | 5550 | 13K | |||
| f = 16 MHz, CL = 20pF, XOSC.GAIN = 3, ESR = 25Ω | - | 6750 | 14.5K | |||
| f = 32MHz, CL = 18pF, XOSC.GAIN = 4, ESR = 40Ω | - | 5.3K | 9.6K |
