PRELIMINARY
CYW54907
3.2 External Frequency Reference
As an alternative to a crystal, an external precision frequency reference can be used, provided that it meets the phase noise require-
ments listed in Table 3.
If used, the external clock should be connected to the WRF_XTAL_XON pin through an external 1000 pF coupling capacitor, as shown
in Figure 5. The internal clock buffer connected to this pin will be turned off when the CYW54907 goes into sleep mode. When the
clock buffer turns on and off, there will be a small impedance variation. Power must be supplied to the WRF_XTAL_VDD1P35 pin.
Figure 5. Recommended Circuit to Use With an External Reference Clock
1000 pF
Reference
WRF_XTAL_XON
Clock
NC
WRF_XTAL_XOP
Table 3. Crystal Oscillator and External Clock—Requirements and Performance
Crystala
External Frequency
Referenceb C
Parameter
Conditions/Notes
Units
MHz
Min.
Typ.
Max.
Min.
Typ.
Max.
Frequency
2.4 GHz and 5 GHz bands:
IEEE 802.11a/b/g/n/ac operation
–
37.4
–
–
37.4
–
Frequency tolerance over the Without trimming
lifetime of the equipment,
–20
–
20
–20
–
20
ppm
including temperaturec
Crystal load capacitance
ESR
–
–
–
–
16
–
–
–
–
–
–
–
–
–
–
–
pF
Ω
60
–
Drive level
External crystal must be able to tolerate 200
this drive level.
–
µW
Input impedance (WRF_X-
TAL_XON)
Resistive
–
–
–
–
–
–
–
30k
–
100k
–
Ω
Capacitive
7.5
–
–
–
7.5
0.2
pF
V
WRF_XTAL_XON
Input low level
DC-coupled digital signal
0
WRF_XTAL_XON
Input high level
DC-coupled digital signal
–
–
–
–
–
–
–
–
–
1.0
400
1
–
–
–
1.26
V
WRF_XTAL_XON input
voltage (see Figure 5)
IEEE 802.11a/b/g operation only
1200 mVp-p
WRF_XTAL_XON input
voltage (see Figure 5)
IEEE 802.11n/ac AC-coupled analog
input
–
Vp-p
Duty cycle
Phase noised
37.4 MHz clock
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
40
–
50
–
60
%
37.4 MHz clock at 10 kHz offset
37.4 MHz clock at 100 kHz offset
37.4 MHz clock at 10 kHz offset
37.4 MHz clock at 100 kHz offset
37.4 MHz clock at 10 kHz offset
37.4 MHz clock at 100 kHz offset
37.4 MHz clock at 10 kHz offset
37.4 MHz clock at 100 kHz offset
–129 dBc/Hz
–136 dBc/Hz
–137 dBc/Hz
–144 dBc/Hz
–134 dBc/Hz
–141 dBc/Hz
–142 dBc/Hz
–149 dBc/Hz
(IEEE 802.11b/g)
Phase noised
–
–
–
–
(IEEE 802.11a)
Phase noised
–
–
–
–
(IEEE 802.11n, 2.4 GHz)
Phase noised
–
–
–
–
(IEEE 802.11n/ac, 5 GHz)
–
–
Document Number: 002-19312 Rev. *C
Page 13 of 95
CYPRESS [ CYPRESS ]
