CYW20738
32 kHz Crystal Oscillator
Figure 7 shows the 32 kHz crystal (XTAL) oscillator with external components and Table 7 on page 14 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 M, 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
W
k
XTAL drive level
For crystal selection
For crystal selection
XTAL series resis- Rseries
tance
70
XTAL shunt capaci- Cshunt
tance
For crystal selection
–
–
1.3
pF
1.12 GPIO Port
The CYW20738 has 22 GPIOs in the 40-pin package, and 40 GPIOs in the 64-pin package. All GPIOs support programmable pull-
up and pull-down resistors, and all support a 2 mAdrive strength except P26, P27, P28, and P29, which provide a 16 mAdrive strength
at 3.3V supply.
1.12.1 Port 0–Port 1, Port 8–Port 23, and Port 28–Port 38
All of these pins can be programmed as ADC inputs.
1.12.2 Port 26–Port 29
P[26:29] consists of four pins. All pins are capable of sinking up to 16 mA for LED. These pins also have the PWM function, which
can be used for LED dimming.
Document Number: 002-14891 Rev. *C
Page 14 of 42
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