Document Number: 002-14874 Rev. *S

Page 11 of 51

CYW20734

Table 5

 shows the recommended crystal specifications.

1.6.2 HID Peripheral Block

The peripheral blocks of the CYW20734 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.

1.6.3 32 kHz Crystal Oscillator

Figure 4 shows the 32 kHz XTAL oscillator with external components and Table 6 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 and C1 = C2 = ~10 pF. The values of C1 and C2 are used to fine-tune the oscillator.

Figure 4. 32 kHz Oscillator Block Diagram

Table 5. Reference Crystal Electrical Specifications

Parameter

Conditions

Minimum

Typical

Maximum

Unit

Nominal frequency

–

–

24.000

–

MHz

Oscillation mode

–

Fundamental

–

Frequency tolerance

@25°C

–

±10

–

ppm

Tolerance stability over temp

@0°C to +70°C

–

±10

–

ppm

Equivalent series resistance

–

–

–

50



Load capacitance

–

–

12

–

pF

Operating temperature range

–

0

–

+70

°C

Storage temperature range

–

–40

–

+125

°C

Drive level

–

–

–

200

μW

Aging

–

–

–

±10

ppm/year

Shunt capacitance

–

–

–

2

pF

C2

C1

R1

32.768 kHz

XTAL