VCT 38xxA
ADVANCE INFORMATION
6.7.2.3. Recommended Crystal Characteristics
Symbol
Parameter
Min.
Typ.
Max.
65
Unit
°C
T
Operating Ambient Temperature
0
–
–
A
f
Parallel Resonance Frequency
20.250000
–
MHz
P
with Load Capacitance C = 13 pF
L
∆f /f
Accuracy of Adjustment
Frequency Temperature Drift
Series Resistance
–
–
–
–
–
–
±20
±30
25
ppm
ppm
Ω
P
P
P
∆f /f
–
P
R
C
C
–
R
0
1
Shunt Capacitance
3
7
pF
Motional Capacitance
20
30
fF
Load Capacitance Recommendation
1)
C
External Load Capacitance from pins to
Ground
–
3.3
–
pF
Lext
(pin names: Xtal1 Xtal2)
2,3)
DCO Characteristics
C
Effective Load Capacitance @ min. DCO–
Position, Code 0,
package: 64PSDIP
3
4.3
5.5
15
pF
pF
ICLoadmin
C
Effective Load Capacitance Range,
DCO Codes from 0..255
11
12.7
ICLoadrng
1)
Remarks on defining the External Load Capacitance:
External capacitors at each crystal pin to ground are required. They are necessary to tune the effective load capacitance of the PCBs to the
required load capacitance C of the crystal. The higher the capacitors, the lower the clock frequency results. The nominal free running fre-
L
quency should match f MHz. Due to different layouts of customer PCBs the matching capacitor size should be determined in the application.
p
The suggested value is a figure based on experience with various PCB layouts.
Tuning condition: Code DVCO Register=–720
2)
Remarks on Pulling Range of DCO:
The pulling range of the DCO is a function of the used crystal and effective load capacitance of the IC (C
+C
). The resulting fre-
LoadBoard
ICLoad
quency f with an effective load capacitance of C
= C
+ C
is:
L
Leff
ICLoad
LoadBoard
1 + 0.5 * [ C / (C + C ) ]
1
0
Leff
f = f * _______________________
L
P
1 + 0.5 * [ C / (C + C ) ]
1
0
L
3)
Remarks on DCO codes
The DCO hardware register has 8 bits, the fp control register uses a range of –2048...2047
152
Micronas
MICRONAS [ MICRONAS ]
