CP3BT26 Datasheet, PDF (52/278 Pages) National Semiconductor (TI) – Reprogrammable Connectivity Processor with Bluetooth-R, USB, and CAN Interfaces

11.1 EXTERNAL CRYSTAL NETWORK
An external crystal network is connected to the X1CKI and
X1CKO pins to generate the Main Clock, unless an external
clock signal is driven on the X1CKI pin. A similar external
crystal network may be used at pins X2CKI and X2CKO for
the Slow Clock. If an external crystal network is not used for
the Slow Clock, the Slow Clock is generated by dividing the
fast Main Clock.
The crystal network you choose may require external com-
ponents different from the ones specified in this datasheet.
In this case, consult with National’s engineers for the com-
ponent specifications
The crystals and other oscillator components must be
placed close to the X1CKI/X1CKO and X2CKI/X2CKO de-
vice input pins to keep the printed trace lengths to an abso-
lute minimum.
Figure 5 shows the external crystal network for the X1CKI
and X1CKO pins. Figure 6 shows the external crystal net-
work for the X2CKI and X2CKO pins. Table 21 shows the
component specifications for the main crystal network, and
Table 22 shows the component specifications for the 32.768
kHz crystal network.
12 MHz
Crystal
X1CKI
C1
X1CKO
C2
GND
DS189
Figure 5. Main Clock External Crystal Network
X2CKI
C1
32.768 kHz
Crystal
X2CKO
C2
GND
DS215
Figure 6. Slow Clock External Crystal Network
Table 21 Component Values of the High Frequency Crystal Circuit
Component
Crystal
Capacitor C1, C2
Parameters
Resonance Frequency
Type
Max. Serial Resistance
Max. Shunt Capacitance
Load Capacitance
Capacitance
Values
12 MHz ± 20 ppm
AT-Cut
50 Ω
7 pF
22 pF
22 pF
Tolerance
N/A
20%
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