44.12.2.2 External 32KHz Crystal Oscillator (XOSC32K) Characteristics

The following table describes the characteristics for the oscillator when a crystal is connected between XIN32 and XOUT32.

Figure 44-3. 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 datasheet. The capacitance of the external capacitors (CLEXT) can then be computed as follows:

C LEXT = 2 ( C L − C STRAY − C SHUNT )

where CSTRAY is the capacitance of the pins and PCB, CSHUNT is the shunt capacitance of the crystal.

Table 44-39. 32KHz Crystal Oscillator Electrical Characteristics
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(2) Crystal Equivalent Series Resistance - SF = 3

f=32.768kHz,
CL=12.5pF

 - 50 70 kΩ
CXIN32k Parasitic load capacitor - - 2.31 - pF
CXOUT32k - - 2.53 -
tSTARTUP Startup time

f=32.768kHz,
CL=12.5pF

 - 25k 82k cycles
Pon Drive Level (1) - - - 0.1 µW
Note:
  1. These values are based on simulation. They are not covered by production test limits or characterization.
  2. These are based on characterization
Table 44-40. Power Consumption
Symbol Parameters Conditions Ta Min. Typ. Max. Units
IDD Current consumption VDD=3.3V Max. 85°C Typ. 25°C - 311 723 nA
Note: These are based on characterization