zl50011 Zarlink Semiconductor, zl50011 Datasheet - Page 41

• Manufacturer Part Number: zl50011
• Description: Flexible 512 Channel Dx With On-chip Dpll
• Manufacturer: Zarlink Semiconductor

The accuracy of a crystal oscillator circuit depends on the crystal tolerance as well as the load capacitance
tolerance. Typically, for a 20 MHz crystal specified with a 32 pF load capacitance, each 1 pF change in load
capacitance contributes approximately 9 ppm to the frequency deviation. Consequently, capacitor tolerances, and
stray capacitances have a major effect on the accuracy of the oscillator frequency.
The trimmer capacitor may be used to compensate for capacitive effects. If accuracy is not a concern, then the
trimmer may be removed, the 39 pF capacitor may be increased to 56 pF, and a wider tolerance crystal may be
substituted.
The crystal should be a fundamental mode type - not an overtone. The fundamental mode crystal permits a simpler
oscillator circuit with no additional filter components and is less likely to generate spurious responses. The crystal
accuracy only affects the output clock accuracy in the freerun mode. The crystal specification is as follows.
Frequency:
Tolerance:
Oscillation Mode:
Resonance Mode:
Load Capacitance:
Maximum Series Resistance:
Approximate Drive Level:
e.g., R1B23B32-20.0 MHz
(20 ppm absolute, ±6 ppm 0C to 50C, 32 pF, 25 Ω)
3.2
When an external clock oscillator is used, numerous parameters must be considered. This includes absolute
frequency, frequency change over temperature, output rise and fall times, output levels and duty cycle.
For applications requiring
FOX F7C-2E3-20.0 MHz
Frequency:
Tolerance:
Rise & Fall Time:
Duty Cycle:
The output clock should be connected directly (not AC coupled) to the XTALi input of the device, and the XTALo
output should be left open as shown in Figure 31.
External Clock Oscillator
10 ns (0.33 V 2.97 V 15 pF)
40% to 60%
20 MHz
25 ppm 0C to 70C
±
32 ppm clock accuracy, the following clock oscillator module may be used:
Fundamental
20 MHz
As required
32 pF
Parallel
1mW
35
ZL50011
Figure 31 - External Clock Oscillator Circuit
Ω
XTALo
XTALi
Zarlink Semiconductor Inc.
No Connection
ZL50011
41
20 MHz OUT
+3.3 V
+3.3 V
GND
0.1uF
Data Sheet