zl30109 Zarlink Semiconductor, zl30109 Datasheet - Page 24

• Manufacturer Part Number: zl30109
• Description: Ds1/e1 System Synchronizer With 19.44 Mhz Output
• 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 13.
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 7 and Figure 13 respectively.
6.3
The ZL30109 requires that the 3.3 V rail is not powered-up later than the 1.8 V rail. 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 rail fully first, then power up the 1.8 V rail
2. Power up the 3.3 V rail and 1.8 V rail simultaneously, ensuring that the 3.3 V rail voltage is never lower than the
1.8 V rail voltage minus a few hundred millivolts (e.g., by using a schottky diode or controlled slew rate)
Power Up Sequence
Crystal Oscillator
1
2
3
4
5
6
ZL30109
Table 7 - 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 13 - Crystal Oscillator Circuit
OSCi
OSCo
1 MΩ
Zarlink Semiconductor Inc.
ZL30109
100 Ω
24
20 MHz
20 MHz
as required
fundamental
parallel
as required
50
Ω
1 µH
Data Sheet