ZL50010/GDC ZARLINK [Zarlink Semiconductor Inc], ZL50010/GDC Datasheet - Page 44

• Manufacturer Part Number: ZL50010/GDC
• Description: Flexible 512 Channel DX with Enhanced DPLL
• Manufacturer: ZARLINK [Zarlink Semiconductor Inc]

3.0
In DPLL Master and Freerun modes, the APLL module requires a 20 MHz clock source at the XTALi pin. The
20 MHz clock can be generated by connecting an external crystal oscillator to the XTALi and XTALo pins, or by
connecting an external clock oscillator to the XTALi pin.
If the device is to be used in DPLL Bypass mode only, the 20 MHz clock is not required and the crystal oscillator or
clock oscillator can be omitted. If the crystal oscillator or clock oscillator is omitted, the XTALi pin must be held low
and the XTALo pin must be left unconnected.
3.1
A complete external crystal oscillator circuit made up of a crystal, resistor and capacitors is shown in Figure 31.
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 9ppm 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)
External Crystal Oscillator
Oscillator Requirements
Fundamental
20 MHz
As required
32 pF
ZL50010
Parallel
1 mW
35
1 uH inductor: may improve stability and is optional
Ω
Figure 31 - Crystal Oscillator Circuit
XTALo
XTALi
1 MΩ
Zarlink Semiconductor Inc.
ZL50010
56 pF
44
100 Ω
20 MHz
39 pF
1 uH
3-50 pF
Data Sheet