MT90812 Mitel Networks Corporation, MT90812 Datasheet - Page 33

• Manufacturer Part Number: MT90812
• Description: Integrated Digital Switch (IDX)
• Manufacturer: Mitel Networks Corporation

Advance Information
9.5
The MT90812 can use either a clock or crystal, connecting to pins C8P_C16i and OSCo, as a reference timing
source.
9.5.1
Fig. 19 shows a 8.192MHz clock oscillator, with 32 ppm tolerance, directly connected to C8P_C16i pin of the
MT90812. The output clock should be connected directly (not AC coupled) to the C8P_C16i pin, and the OSCo
output should be left open.
9.5.2
Alternatively, a Crystal Oscillator may be used. A complete oscillator circuit made up of a crystal, resistor and
capacitors is shown in Fig. 20.
The accuracy of a crystal oscillator depends on the crystal tolerance as well as the load capacitance tolerance.
Typically, for a 8.192MHz crystal specified with a 32pF load capacitance, each 1pF 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 shown in Fig. 20 may be used to compensate for capacitive effects. If accuracy is not a
concern, then the trimmer may be removed, the 39pF capacitor may be increased to 56pF, and a wider
tolerance crystal may be substituted.
The crystal should be a fundamental mode type. The fundamental mode crystal permits a simpler oscillator
circuit with no additional filter components and is less likely to generate spurious responses. The crystal
specification is as follows:
Frequency:
Tolerance:
Oscillation Mode:
Resonance Mode:
Load Capacitance:
Maximum Series Resistance:
Approximate Drive Level:
e.g. CTS R1B23B32-8.192MHz
(20ppm absolute 6 ppm 0C to 50C, 32pF, 25
C8P Pin Timing Source
Clock Oscillator
Crystal Oscillator
As required
Fundamental
Parallel
20pF
35
1mW
8.192MHz
Figure 19 - Clock Oscillator Circuit
MT90812
No Connection
OSCo
C8P_C16i
8.192MHz
GND
+5V
+5V
0.1uF
MT90812
29