CYW20732A0
Table 6 shows the recommended crystal specifications.
Table 6. Reference Crystal Electrical Specifications
Parameter
Nominal frequency
Conditions
Minimum
Typical
Maximum
Unit
MHz
–
–
–
24.000
–
Oscillation mode
–
Fundamental
Frequency tolerance
Tolerance stability over temp
Equivalent series resistance
Load capacitance
@25°C
–
–
±10
±10
–
–
–
ppm
ppm
Ω
@0°C to +70°C
–
–
–
–
–
–
–
–
60
–
12
–
–
pF
Operating temperature range
Storage temperature range
Drive level
0
+70
+125
200
±10
2
°C
–40
–
–
°C
–
μW
Aging
–
–
ppm/year
pF
Shunt capacitance
–
–
1.9.2 Peripheral Block
The CYW20732 peripheral blocks 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.
1.9.3 32 kHz Crystal Oscillator
Figure 7 shows the 32 kHz crystal (XTAL) oscillator with external components and Table 7 on page 11 lists the oscillator’s character-
istics. 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
Table 7. XTAL Oscillator Characteristics
Parameter
Symbol
Conditions
Minimum
Typical
32.768
Maximum
Unit
Output frequency Foscout
–
–
–
–
–
kHz
Frequency
tolerance
–
Crystal dependent
100
ppm
Start-up time
Tstartup
Pdrv
–
–
–
–
500
–
ms
XTAL drive level
For crystal selection 0.5
μW
Document Number: 002-14837 Rev. *L
Page 11 of 35
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