CYW20736
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
Table 7. XTAL Oscillator Characteristics
Parameter
Symbol
Conditions
Minimum
Typical
32.768
100
Maximum
Unit
kHz
ppm
Output frequency Foscout
–
–
–
–
–
Frequency
tolerance
–
Crystal dependent
Start-up time
Tstartup
Pdrv
–
–
0.5
–
–
–
–
500
–
ms
μΩ
kΩ
XTAL drive level
For crystal selection
XTAL series
resistance
70
Rseries
Cshunt
For crystal selection
For crystal selection
XTAL shunt
capacitance
–
–
1.3
pF
1.10 GPIO Port
The CYW20736 has 14 general-purpose I/Os (GPIOs) in the 32-pin package. All GPIOs support programmable pull-up and
pull-down resistors, and all support a 2 mA drive strength except P26, P27, and P28, which provide a 16 mA drive strength at 3.3V
supply.
The following GPIOs are available:
■ P0–P4
■ P8/P33 (Dual bonded, only one of two is available.)
■ P11/P27 (Dual bonded, only one of two is available.)
■ P12/P26 (Dual bonded, only one of two is available.)
■ P13/P28 (Dual bonded, only one of two is available.)
■ P14/P38 (Dual bonded, only one of two is available.)
■ P15
■ P24
■ P25
■ P32
Document Number: 002-14883 Rev. *I
Page 12 of 47
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