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:

CLEXT=2(CL−CSTRAY−CSHUNT)

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
SymbolParameterConditionsMin.Typ.Max.Units
FOUTCrystal oscillator frequency--32.768-kHz
CLCrystal load capacitance-7912.5pF
CSHUNTCrystal shunt capacitance-0.6-2pF
CMMotional capacitance-0.6-3fF
ESR(2)Crystal Equivalent Series Resistance - SF = 3

f=32.768kHz,
CL=12.5pF

-5070kΩ
CXIN32kParasitic load capacitor--2.31-pF
CXOUT32k--2.53-
tSTARTUPStartup time

f=32.768kHz,
CL=12.5pF

-25k82kcycles
PonDrive Level (1)---0.1µW
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
SymbolParametersConditionsTaMin.Typ.Max.Units
IDDCurrent consumptionVDD=3.3VMax. 85°C Typ. 25°C-311723nA
Note: These are based on characterization