CYW20737
Table 6. Reference Crystal Electrical Specifications
Parameter Conditions
Nominal frequency
Minimum
Typical
24.000
Maximum
Unit
MHz
–
–
–
Oscillation mode
–
Fundamental
–
Frequency tolerance
Tolerance stability over temp
Equivalent series resistance
Load capacitance
@25°C
–
±10
±10
–
–
ppm
ppm
@0°C to +70°C
–
–
–
–
–
–
–
–
–
–
50
–
–
12
–
pF
Operating temperature range
Storage temperature range
Drive level
0
+70
+125
200
±10
2
°C
–40
–
–
°C
–
μW
ppm/year
pF
Aging
–
–
Shunt capacitance
–
–
Peripheral Block
The peripheral blocks of the CYW20737 all run from a single 128 kHz low-power RC oscillator. The oscillator can be turned on at the
request of any of the peripherals. If the peripheral is not enabled, it shall not assert its clock request line.
The keyboard scanner is a special case, in that it may drop its clock request line even when enabled, and then reassert the clock
request line if a keypress is detected.
32 kHz Crystal Oscillator
Figure 7 shows the 32 kHz crystal (XTAL) oscillator with external components and Table 7 lists the oscillator’s
characteristics. It is a standard Pierce oscillator using a comparator with hysteresis on the output to create a single-
ended digital output. The hysteresis was added to eliminate any chatter when the input is around the threshold of the
comparator and is ~100 mV. This circuit can be operated with a 32 kHz or 32.768 kHz crystal oscillator or be driven with
a clock input at similar frequency. The default component values are: R1 = 10 MΩ, C1 = C2 = ~10 pF. The values of C1
and C2 are used to fine-tune the oscillator.
Figure 7. 32 kHz Oscillator Block Diagram
C2
32.768 kHz
R1
XTAL
C1
Document Number: 002-16365 Rev. *C
Page 13 of 36
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