54.13.2 External 32 kHz 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 54-46. Digital Clock Characteristics(1)
SymbolParameterMin.Typ.Max.Units
fCPXIN32XIN32 clock frequency32.768kHz
DCXINXIN32 clock duty cycle50%
Note: 1.These values are based on simulation. They are not covered by production test limits or characterization.

Crystal Oscillator Characteristics

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

Figure 54-6. 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] * [CXOUT32K + CLEXT]) / ([CXIN32K + CLEXT + CLEXT + CXOUT32K]) + CSTRAY

Where:

CLOAD = Crystal Mfg. CLOAD specification.

CXIN32k = XIN32 capacitance, see the following table.

CXOUT32k = XOUT32 pin capacitance, see the following table.

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 54-47. 32 kHz Crystal Oscillator Electrical Characteristics (2)
SymbolParameterConditionsMin.Typ.Max.Units
FOUT(1)Crystal oscillator frequency--32.768-kHz
CL(1)Crystal load capacitance---12.5pF
ESRCrystal Equivalent Series Resistance - SF=3

f=32.768 kHz,
CL=12.5 pF

Std. Gain--58kΩ
High Gain--90
CXIN32kXIN32 pin capacitance--3.1-pF
CXOUT32kXOUT32 pin capacitance--3.2-
Note:
  1. These values are based on simulation. They are not covered by production test limits or characterization.
  2. Maximum start up time that can be programmed in OSC32KCTRL.STARTUP is 8s.
Table 54-48. Power Consumption
SymbolParameterConditionsTaGain ModeTyp.Max.Units
IDDCurrent consumption VDD=3.0V Max 85°C

Typ 25°C

Std.1.52µA
High1.93