MPC9230 データシートの表示（PDF） - Integrated Device Technology

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MPC9230

800MHz Low Voltage PECL Clock Synthesizer

Integrated Device Technology 

MPC9230 Data Sheet

800MHZ LOW VOLTAGE PECL CLOCK SYNTHESIZER

and bypass schemes discussed in this section should be adequate

to eliminate power supply noise related problems in most designs.

C1

C1

1

CF

C2

XTAL

= VCC

= GND

= Via

Figure 6. PCB Board Layout Recommendation for

the PLCC28 Package

Using the On-Board Crystal Oscillator

The MPC9230 features a fully integrated on-board crystal

oscillator to minimize system implementation costs. The oscillator is

a series resonant, multivibrator type design as opposed to the more

common parallel resonant oscillator design. The series resonant

design provides better stability and eliminates the need for large on-

chip capacitors. The oscillator is totally self contained so that the

only external component required is the crystal. As the oscillator is

somewhat sensitive to loading on its inputs, the user is advised to

mount the crystal as close to the MPC9230 as possible to avoid any

board level parasitics. To facilitate co-location, surface mount

crystals are recommended but not required. Because the series

resonant design is affected by capacitive loading on the XTAL

terminals, loading variation introduced by crystals from different

vendors could be a potential issue. For crystals with a higher shunt

capacitance, it may be required to place a resistance across the

terminals to suppress the third harmonic. Although typically not

required, it is a good idea to layout the PCB with the provision of

adding this external resistor. The resistor value will typically be

between 500 and 1 KΩ.

The oscillator circuit is a series resonant circuit and thus for

optimum performance a series resonant crystal should be used.

Unfortunately, most crystals are characterized in a parallel resonant

mode. Fortunately, there is no physical difference between a series

resonant and a parallel resonant crystal. The difference is purely in

the way the devices are characterized. As a result, a parallel

resonant crystal can be used with the MPC9230 with only a minor

error in the desired frequency. A parallel resonant mode crystal used

in a series resonant circuit will exhibit a frequency of oscillation a few

hundred ppm lower than specified; a few hundred ppm translates to

kHz inaccuracies. In a general, computer application at this level of

inaccuracy is immaterial. Table 14 below specifies the performance

requirements of the crystals to be used with the MPC9230.

Table 14. Recommended Crystal Specifications

Parameter

Crystal Cut

Resonance

Frequency Tolerance

Frequency/Temperature Stability

Operating Range

Shunt Capacitance

Equivalent Series Resistance (ESR)

Correlation Drive Level

Aging

Value

Fundamental AT Cut

Series Resonance(1)

±75 ppm at 25°C

±150 pm 0 to 70°C

0 to 70°C

5–7 pF

50 to 80 Ω

100 µΩ

5 ppm/Yr (First 3 Years)

1. See accompanying text for series versus parallel resonant

discussion.

MPC9230 REVISION 8 MARCH 29, 2010

11

©2010 Integrated Device Technology, Inc.

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