MOTOROLA

TIMING SOLUTIONS

8

Figure 3. Configuration for 125 MHz clocks

Figure 4. Configuration for 133.3/66.67 MHz clocks

MPC9600

fref = 20.833 MHz

125 MHz

125 MHz

20.833 MHz (Feedback)

125 MHz

Frequency range

Min

Max

Input

16.67 MHz

33.33 MHz

QA outputs

100 MHz

200 MHz

QB outputs

100 MHz

200 MHz

QC outputs

100 MHz

200 MHz

Frequency range

Min

Max

Input

25 MHz

50 MHz

QA outputs

100 MHz

200 MHz

QB outputs

100 MHz

200 MHz

QC outputs

100 MHz

200 MHz

CCLK

FB_IN

FSEL_FB

FSELA

FSELB

FSELC

QA0–6

QB0–6

QC0–6

QFB

7

7

7

1

0

0

0

MPC9600

fref = 33.33 MHz

133.3 MHz

66.67 MHz

33.33 MHz (Feedback)

66.67 MHz

CCLK

FB_IN

FSEL_FB

FSELA

FSELB

FSELC

QA0–6

QB0–6

QC0–6

QFB

7

7

7

0

0

1

1

Power Supply Filtering

The MPC9600 is a mixed analog/digital product. Its analog

circuitry is naturally susceptible to random noise, especially if

this noise is seen on the power supply pins. Random noise

on the VCCA (PLL) power supply impacts the device

characteristics, for instance I/O jitter. The MPC9600 provides

separate power supplies for the output buffers (VCC) and the

phase-locked loop (VCCA) of the device.The purpose of this

design technique is to isolate the high switching noise digital

outputs from the relatively sensitive internal analog

phase-locked loop. In a digital system environment where it

is more difficult to minimize noise on the power supplies a

second level of isolation may be required. The simple but

effective form of isolation is a power supply filter on the VCCA

pin for the MPC9600. Figure 5. illustrates a typical power

supply filter scheme. The MPC9600 frequency and phase

stability is most susceptible to noise with spectral content in

the 100kHz to 20MHz range. Therefore the filter should be

designed to target this range. The key parameter that needs

to be met in the final filter design is the DC voltage drop

across the series filter resistor RF. From the data sheet the

ICCA current (the current sourced through the VCCA pin) is

typically 3 mA (5 mA maximum), assuming that a minimum of

2.325 V (VCC=3.3 V or VCC=2.5 V) must be maintained on

the VCCA pin. The resistor RF shown in Figure 5. “VCCA

Power Supply Filter” must have a resistance of 9-10

W

(VCC=2.5 V) to meet the voltage drop criteria.

The minimum values for RF and the filter capacitor CF are

defined by the required filter characteristics: the RC filter

should provide an attenuation greater than 40 dB for noise

whose spectral content is above 100 kHz. In the example RC

filter shown in Figure 5. “VCCA Power Supply Filter”, the filter

cut-off frequency is around 3-5 kHz and the noise attenuation

at 100 kHz is better than 42 dB.

Figure 5. VCCA Power Supply Filter

VCCA

VCC

MPC9600

10 nF

RF = 9–10 Ω for VCC = 2.5 V or VCC = 3.3 V

CF

33...100 nF

RF

VCC

CF = 22 µF for VCC = 2.5 V or VCC = 3.3 V

As the noise frequency crosses the series resonant point

of an individual capacitor its overall impedance begins to look

inductive and thus increases with increasing frequency. The

parallel capacitor combination shown ensures that a low

impedance path to ground exists for frequencies well above

the bandwidth of the PLL. Although the MPC9600 has

several design features to minimize the susceptibility to

power supply noise (isolated power and grounds and fully

differential PLL) there still may be applications in which

overall performance is being degraded due to system power

supply noise. The power supply filter schemes discussed in

this section should be adequate to eliminate power supply

noise related problems in most designs.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com