46.12.2 External 32KHz Crystal Oscillator (XOSC32K) Characteristics
Digital Clock Characteristics
The following table describes the characteristics for the oscillator when a digital clock is applied on XIN32 pin.
| Symbol | Parameter | Min. | Typ. | Max. | Units |
|---|---|---|---|---|---|
| fCPXIN32 | XIN32 clock frequency | 32.768 | 1000 | kHz | |
| DCXIN | XIN32 clock duty cycle | 40 | 50 | 60 | % |
Crystal Oscillator Characteristics
The following table describes the characteristics for the oscillator when a crystal is connected between XIN and XOUT as shown in the figure Oscillator Connection.
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 | - | - | 32.768 | - | kHz |
| CL | Crystal load capacitance | - | 7 | 9 | 12.5 | pF |
| CSHUNT | Crystal shunt capacitance | - | 0.6 | - | 2 | pF |
| CM | Motional capacitance | - | 0.6 | - | 3 | fF |
| ESR | Crystal Equivalent Series Resistance - SF=3 |
f=32.768kHz, | - | 50 | 70 | kΩ |
| CXIN32k | Parasitic load capacitor(2) | - | - | 2.31 | - | pF |
| CXOUT32k | - | - | 2.53 | - | ||
| tSTARTUP | Startup time |
f=32.768kHz, | - | 25k | 82k | Cycles |
| Pon | Drive Level (1) | - | - | - | 0.1 | µW |
- These values are based on simulation. They are not covered by production test limits or characterization.
- For device revision A, see Erratum 13425.
| Symbol | Parameter | Conditions | Ta | Min. | Typ. | Max. | Units |
|---|---|---|---|---|---|---|---|
| IDD | Current consumption | VCC=3.3V | Max 85°C Typ 25°C | - | 311 | 723 | nA |