15.12.2 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.

Table 15-36. Digital Clock Characteristics(1)
Symbol Parameter Min. Typ. Max. Units
fCPXIN32 XIN32 clock frequency 32.768 1000 kHz
DCXIN XIN32 clock duty cycle 40 50 60 %
Note: 1. These values are based on characterization.

Crystal Oscillator Characteristics

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

Figure 15-4. Oscillator Crystal 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 - SHUNT) ,

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

Table 15-37. 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 Crystal Equivalent Series Resistance - SF=3

f=32.768kHz,
CL=12.5pF

 - 50 70 kΩ
CXIN32k Parasitic load capacitor(2) - - 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. For device revision A, see Erratum 13425.
Table 15-38. Power Consumption(1)
Symbol Parameter Conditions Ta Min. Typ. Max. Units
IDD Current consumption VCC=3.3V Max 85°C

Typ 25°C

 - 311 723 nA
Note: (1) These values are based on characterization.