BCM4390DKWBGT Datasheet, PDF (19/78 Pages) Cypress Semiconductor – WICED™ Wi-Fi IEEE 802.11 b/g/n SoC with Embedded Application Processor

BCM4390 Advance Data Sheet
External Frequency Reference
External Frequency Reference
As an alternative to a crystal, an external precision frequency reference can be used, provided that it meets the
Phase Noise requirements listed in Table 2.
If used, the external clock should be connected to the WRF_XTAL_IN 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
BCM4390 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_BUCK_VDD1P5 pin.
Figure 5: Recommended Circuit to Use with an External Reference Clock
Reference
Clock
1000 pF
NC
WRF_XTAL_IN
WRF_XTAL_OUT
Table 2: Crystal Oscillator and External Clock – Requirements and Performance
Crystal^a
External Frequency
Reference^{b c}
Parameter
Conditions/Notes
Min Typ Max Min Typ Max Units
Frequency
IEEE 802.11 b/g/n operation
Frequency tolerance Without trimming
over the lifetime of
the equipment,
including
temperature^e
Between 19 MHz and 52 MHz^d
–20 – 20 –20 –
20 ppm
Crystal load
–
capacitance
ESR
–
–
12 –
–
–
–
pF
–
–
60 –
–
–
Ω
Drive level
External crystal must be able to 200 – – – – – µW
tolerate this drive level.
Input impedance
(WRF_XTAL_IN)
WRF_XTAL_IN
Input low level
WRF_XTAL_IN
Input high level
Resistive
Capacitive
DC-coupled digital signal
DC-coupled digital signal
–
–
–
30K 100K –
Ω
–
–
7.5 –
–
7.5 pF
–
–
–
0
–
0.2 V
–
–
–
1.0 –
1.26 V
WRF_XTAL_IN
input voltage
(see Figure 5)
AC-coupled analog signal
–
–
–
400 –
1200 mV_p-p
BROADCOM ®
February 5, 2014 • 4390-DS103-R
WICED Wi-Fi IEEE 802.11 SoC w/Embedded App Processor
Page 18
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