47.6.2 External 32.768 kHz Crystal Oscillator (XOSC32K) Characteristics
The following table describes the characteristics for the oscillator when a digital clock is applied on XIN32 pin.
| Symbol | Parameter | Condition | Typ | Units |
|---|---|---|---|---|
| fCPXIN32 | XIN32 clock frequency | Digital mode | 32.768 | kHz |
| DCXIN32 | XIN32 clock duty cycle | Digital mode | 50 | % |
- These are based on simulation. These values are not covered by test or characterization
The following table describes the characteristics for the oscillator when a crystal is connected between XIN32 and XOUT32.
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:
CLEXT=2(CL-CSTRAY-CSHUNT)
where CSTRAY is the capacitance of the pins and
PCB and CSHUNT is the shunt capacitance of the crystal.
| Symbol | Parameter | Conditions | Min. | Typ. | Max | Units |
|---|---|---|---|---|---|---|
| fOUT (1) | Crystal oscillator frequency | - | 32768 | - | Hz | |
| CL (1) | Crystal load capacitance | - | - | 12.5 | pF | |
| CSHUNT (1) | Crystal shunt capacitance | - | - | 1.75 | pF | |
| CM (1) | Motional capacitance | - | 1.25 | - | fF | |
| ESR | Crystal Equivalent Series Resistance - SF = 3 | F = 32.768 kHz, CL=12.5 pF | - | - | 70 | kΩ |
| CXIN32K | Parasitic capacitor load | - | 3.8 | - | pF | |
| CXOUT32K | - | 4.1 | - | pF | ||
| TSTART | Startup time | F = 32.768 kHz, CL=12.5 pF | - | 16 | 24 | Kcycles |
- These are based on simulation. These values are not covered by test or characterization