PRELIMINARY
CYW54907
3. Frequency References
An external crystal is used for generating all radio frequencies and normal-operation clocking. As an alternative, an external frequency
reference can be used. In addition, a low-power oscillator (LPO) is provided for lower power mode timing.
3.1 Crystal Interface and Clock Generation
The CYW54907 can use an external crystal to provide a frequency reference. The recommended crystal oscillator configuration,
including all external components, is shown in Figure 4. Consult the reference schematics for the latest configuration.
Figure 4. Recommended Oscillator Configuration
Device boundary
C
WRF_XTAL_XON
1.3 pF
27 pF
Programmable internal shunt caps are
from 0 pF to 7.5 pF in steps of 0.5 pF.
37.4 MHz
C
WRF_XTAL_XOP
x ohms
0.4 pF
27 pF
External resistor and programmable
internal resistor value is determined
by crystal drive level.
Programmable internal series resistor is from 50 ohms to 500 ohms
in steps of 50 ohms. Boot‐up ROM value is 50 ohms.
Note: A reference schematic is available for further details. Contact your Cypress FAE.
A fractional-N synthesizer in the CYW54907 generates the radio frequencies, clocks, and data/packet timing, enabling it to operate
using a wide selection of frequency references.
The recommended default frequency reference is a 37.4 MHz crystal. The signal characteristics for the crystal interface are listed in
Table 3.
Note: Although the fractional-N synthesizer can support alternative reference frequencies, frequencies other than the default require
support to be added in the driver, plus additional extensive system testing. Contact Cypress for further details.
Document Number: 002-19312 Rev. *C
Page 12 of 95
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