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 1. 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 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 1. 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 data sheet. The capacitance of the external capacitors (C_LEXT) can then be computed as follows:

C_LEXT = 2(C_L - C_PARA - C_PCB - C_SHUNT)

Where:

C_PARA is the internal load capacitor parasitic between XIN and XOUT ( C_PARA = (C_XIN32K C_XOUT32K)/(C_XIN32K + C_XOUT32K) )
C_PCB is the capacitance of the PCB
C_SHUNT is the shunt capacity of the crystal.

Table 2. 32 KHz Crystal Oscillator Electrical Characteristics
Symbol	Parameter	Conditions	Min.	Typ.	Max.	Units
F_OUT	Crystal oscillator frequency	-	-	32.768	-	kHz
CL⁽¹⁾	Crystal load capacitance	-	7	-	9	pF
C_SHUNT⁽¹⁾	Crystal shunt capacitance	-	0.6	-	2	pF
C_M⁽¹⁾	Motional capacitance	-	0.6	-	3	fF
ESR⁽²⁾	Crystal Equivalent Series Resistance - SF=3	f=32.768kHz, C_L= 9pF	-	-	70	kΩ
C_XIN32k⁽²⁾	Parasitic load capacitor	-	-	3.2	-	pF
C_XOUT32k⁽²⁾	Parasitic load capacitor	-	-	3.4	-	pF
t_STARTUP⁽²⁾	Startup time	f=32.768kHz, C_L= 9pF	-	10	43	KCycles
P_on⁽¹⁾	Drive Level	-	-	-	0.1	µW

Notes:

1.These values are based on simulation. They are not covered by production test limits or characterization.
2.These values are based on characterization. They are not covered in test limits in production.

Table 3. Power Consumption ⁽¹⁾
Symbol	Parameter	Conditions	Ta	Min.	Typ.	Max.	Units
I_DD	Current consumption	VCC=3.3V	Max 85°C Typ 25°C	-	309	606	nA

Note:

1.These values are based on characterization. They are not covered in test limits in production.