47.8.2 External 32KHz Crystal Oscillator (XOSC32K) Characteristics - 105°C

Digital Clock Characteristics

The following table describes the characteristics for the oscillator when a digital clock is applied on XIN32 pin.

Table 47-31. Digital Clock Characteristics(1)
SymbolParameterMin.Typ.Max.Units
fCPXIN32XIN32 clock frequency32.7681000kHz
DCXINXIN32 clock duty cycle405060%
Note: 1. These values are based on characterization.

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.

Figure 47-3. 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 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)

Table 47-32. 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
ESRCrystal Equivalent Series Resistance - SF=3

f=32.768kHz,
CL=12.5pF

-5070kΩ
CXIN32kParasitic load capacitor(2)--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 characterization.
Table 47-33. Power Consumption(1)
SymbolParameterConditionsTaMin.Typ.Max.Units
IDDCurrent consumption VCC=3.3V Max 105°C

Typ 25°C

-0.311755nA
Note: (1) These values are based on characterization.