SC2200 NSC [National Semiconductor], SC2200 Datasheet - Page 94

• Manufacturer Part Number: SC2200
• Description: Thin Client On a Chip
• Manufacturer: NSC [National Semiconductor]

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General Configuration Block
3.5.1
The internal oscillator employs an external crystal con-
nected to the on-chip amplifier. The on-chip amplifier is
accessible on the X27I input and X27O output signals. See
Figure 3-3 for the recommended external circuit and Table
3-5 for a list of the circuit components.
Choose C
capacitance. The load capacitance C
is comprised of C
parasitic capacitance of the circuit. The parasitic capaci-
tance is caused by the chip package, board layout and
socket (if any), and can vary from 0 to 10 pF. The rule of
thumb in choosing these capacitors is:
Example 1:
Example 2:
1.
Component
Crystal
Resistor R
Resistor R
Capacitor C
Capacitor C
C
Crystal C
C
Crystal C
C
The value of these components is recommended. It should be tuned according to crystal and board parameters.
L
1
1
= (C
= 3.6 pF, C
= 24 pF, C
27 MHz Crystal Oscillator
1
1
1
2
and C
1
1
2
* C
L
L
1
1
= 10 pF, C
= 20 pF, C
2
1
) / (C
2
2
2
in series with C
= 24 pF
= 3.6 pF
capacitors to match the crystal’s load
Parameters
Resonance Frequency
Type
Serial Resistance
Shunt Capacitance
Load Capacitance, C
Temperature Coefficient
Resistance
Resistance
Capacitance
Capacitance
1
+ C
PARASITIC
PARASITIC
2
) + C
Table 3-5. Crystal Oscillator Circuit Components
PARASITIC
2
= 8.2 pF
= 8 pF
and in parallel with the
L
“seen” by crystal Y
(Continued)
L
94
Values
27.00 MHz Parallel mode
AT-cut or BT-cut
10-20 pF
User-defined
20 M
100
3-24 pF
3-24 pF
40
7 pF
Figure 3-3. Recommended Oscillator External
X27I
C
Circuitry
1
R
Y
1
50 PPM or better
Tolerance
Max
Max
5%
5%
5%
5%
R
2
C
X27O
2
To other
modules
External
Internal
Revision 3.0