BCM20705 Datasheet, PDF (38/67 Pages) Cypress Semiconductor – Single-Chip Bluetooth Transceiver and Baseband Processor

BCM20705 Data Sheet
Crystal Oscillator
Crystal Oscillator
The BCM20705 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 7.
Figure 7: Recommended Oscillator Configuration
XIN
0 ~18 pF*
Crystal
Oscillator
XOUT
0 ~18 pF*
*Capacitor value range depends
on the manufacturer of the XTAL
as well as board layout.
External Frequency Reference
An external frequency reference, such as VDD_RF, collectively refers to several RF power supplies generated
by a TCXO signal that may be directly connected to the crystal input pin on the BCM20705, as shown in
Figure 8. The external frequency reference input is designed to not change loading on the TCXO when the
BCM20705 is powered up or powered down.
When using the BCM20705 with the TXCO OR gate option, GPIO 6 must be driven active high or active low.
Excessive leakage current results if GPIO6 is allowed to float.
Figure 8: Recommended TCXO Connection
TCXO
10–1000 pF*
No Connection
* Recommended value is 100 pF.
Higher values produce a longer startup time.
Lower values have greater isolation.
Larger values help small signal swings.
XIN
XOUT
Broadcom®
Bluetooth Transceiver and Baseband Processor
November 13, 2014 • MCS20705-DS104-R
Page 37
BROADCOM CONFIDENTIAL