BCM20730 Data Sheet
Clock Frequencies
Table 5: Reference Crystal Electrical Specifications
Parameter
Conditions
Minimum Typical
24.000
Fundamental
Maximum Unit
Nominal frequency
Oscillation mode
–
–
–
–
MHz
–
Frequency tolerance
@25°C
–
±10
–
ppm
ppm
W
Tolerance stability over temp @0°C to +70°C
Equivalent series resistance
Load capacitance
–
–
–
±10
–
12
–
–
–
–
50
–
–
–
–
–
–
–
–
pF
Operating temperature range
Storage temperature range
Drive level
0
–40
–
+70
+125
200
±10
2
°C
°C
μW
ppm/year
pF
Aging
Shunt capacitance
–
–
–
–
HID Peripheral Block
The peripheral blocks of the BCM20730 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 6 on page 27 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
BROADCOM
®
September 9, 2013 • 20730-DS108-R
Page 26
BROADCOM CONFIDENTIAL
CYPRESS [ CYPRESS ]
