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
f_CPXIN32	XIN32 clock frequency		32.768	1000	kHz
DC_XIN	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 C_L is within the range given in the table. The exact value of C_L can be found in the crystal datasheet. The capacitance of the external capacitors (C_LEXT) can then be computed as follows:

C_LEXT = 2(C_L - C_STRAY - _SHUNT) ,

where C_STRAY is the capacitance of the pins and PCB, C_SHUNT is the shunt capacitance of the crystal.

Table 15-37. 32KHz Crystal Oscillator Electrical Characteristics
Symbol	Parameter	Conditions	Min.	Typ.	Max.	Units
F_OUT	Crystal oscillator frequency	-	-	32.768	-	kHz
CL	Crystal load capacitance	-	7	9	12.5	pF
C_SHUNT	Crystal shunt capacitance	-	0.6	-	2	pF
C_M	Motional capacitance	-	0.6	-	3	fF
ESR	Crystal Equivalent Series Resistance - SF=3	f=32.768kHz, C_L=12.5pF	-	50	70	kΩ
C_XIN32k	Parasitic load capacitor⁽²⁾	-	-	2.31	-	pF
C_XOUT32k	Parasitic load capacitor⁽²⁾	-	-	2.53	-	pF
t_STARTUP	Startup time	f=32.768kHz, C_L=12.5pF	-	25k	82k	Cycles
P_on	Drive Level ⁽¹⁾	-	-	-	0.1	µW

Note:

These values are based on simulation. They are not covered by production test limits or characterization.
For device revision A, see Erratum 13425.

Table 15-38. Power Consumption⁽¹⁾
Symbol	Parameter	Conditions	Ta	Min.	Typ.	Max.	Units
I_DD	Current consumption	VCC=3.3V	Max 85°C Typ 25°C	-	311	723	nA

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