zl30102 Zarlink Semiconductor, zl30102 Datasheet - Page 33

• Manufacturer Part Number: zl30102
• Description: T1/e1 Stratum 4/4e Redundant System Clock Synchronizer For Ds1/e1 And H.110
• Manufacturer: Zarlink Semiconductor

6.2.2
Alternatively, a Crystal Oscillator may be used. A complete oscillator circuit made up of a crystal, resistor and
capacitors is shown in Figure 20.
The accuracy of a crystal oscillator 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 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. A typical
crystal oscillator specification and circuit is shown in Table 8 and Figure 20 respectively.
6.3
The ZL30102 requires that the 3.3 V supply is not powered up after the 1.8 V supply. This is to prevent the risk of
latch-up due to the presence of parasitic diodes in the IO pads.
Two options are given:
1. Power-up the 3.3 V supply fully first, then power up the 1.8 V supply
2. Power up the 3.3 V supply and the 1.8 V supply simultaneously, ensuring that the 3.3 V supply is never lower
than a few hundred millivolts below the 1.8 V supply (e.g., by using a schottky diode or controlled slew rate)
Power Up Sequence
Crystal Oscillator
1
2
3
4
5
6
ZL30102
Table 8 - Typical Crystal Oscillator Specification
Frequency
Tolerance
Oscillation mode
Resonance mode
Load capacitance
Maximum series resistance
The 100 Ω resistor and the 1 µH inductor may improve
stability and are optional.
Figure 20 - Crystal Oscillator Circuit
OSCi
OSCo
1 MΩ
Zarlink Semiconductor Inc.
ZL30102
100 Ω
33
20 MHz
20 MHz
as required
fundamental
parallel
as required
50
Ω
1 µH
Data Sheet
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