PRELIMINARY
CYW43438
3. Frequency References
An external crystal is used for generating all radio frequencies and normal operation clocking. As an alternative, an external frequency
reference driven by a temperature-compensated crystal oscillator (TCXO) signal may be used. No software settings are required to
differentiate between the two. In addition, a low-power oscillator (LPO) is provided for lower power mode timing.
3.1 Crystal Interface and Clock Generation
The CYW43438 can use an external crystal to provide a frequency reference. The recommended configuration for the crystal oscillator,
including all external components, is shown in Figure 5. Consult the reference schematics for the latest configuration.
Figure 5. Recommended Oscillator Configuration
C
WLRF_XTAL_XOP
12 – 27 pF
C
WLRF_XTAL_XON
R
12 – 27 pF
Note: Resistor value determined by crystal drive level.
See reference schematics for details.
The CYW43438 uses a fractional-N synthesizer to generate the radio frequencies, clocks, and data/packet timing so that it can operate
using numerous frequency references. The frequency reference can be an external source such as a TCXO or a crystal interfaced
directly to the CYW43438.
The default frequency reference setting is a 37.4 MHz crystal or TCXO. The signal requirements and characteristics for the crystal
interface are shown in Table 3.
Note: Although the fractional-N synthesizer can support many reference frequencies, frequencies other than the default require
support to be added in the driver, plus additional extensive system testing. Contact Broadcom for further details.
3.2 TCXO
As an alternative to a crystal, an external precision TCXO can be used as the frequency reference, provided that it meets the phase
noise requirements listed in Table 3.
If the TCXO is dedicated to driving the CYW43438, it should be connected to the WLRF_XTAL_XOP pin through an external capacitor
with value ranges from 200 pF to 1000 pF as shown in Figure 6.
Figure 6. Recommended Circuit to Use with an External Dedicated TCXO
200 pF – 1000 pF
TCXO
WLRF_XTAL_XOP
WLRF_XTAL_XON
NC
Document Number: 002-14796 Rev. *K
Page 13 of 101
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