MPC953FAR2 Freescale Semiconductor, MPC953FAR2 Datasheet - Page 4

• Manufacturer Part Number: MPC953FAR2
• Description: IC PLL CLOCK DRIVER 32-LQFP
• Manufacturer: Freescale Semiconductor
• Type: Clock Driver, Fanout Distribution, Multiplexer , Zero Delay Bufferr

Specifications of MPC953FAR2

• Pll: Yes
• Input: LVCMOS, LVPECL, LVTTL
• Output: LVCMOS
• Number Of Circuits: 1
• Ratio - Input:output: 2:9
• Differential - Input:output: Yes/No
• Frequency - Max: 110MHz
• Divider/multiplier: Yes/No
• Voltage - Supply: 3.135 V ~ 3.465 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 32-LQFP
• Frequency-max: 110MHz
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: MPC953FATR

Power Supply Filtering
such it exhibits some sensitivities that would not necessarily
be seen on a fully digital product. Analog circuitry is naturally
susceptible to random noise, especially if this noise is seen
on the power supply pins. The MPC953 provides separate
power supplies for the output buffers (VCCO) and the
phase–locked loop (VCCA) of the device. The purpose of this
design technique is to try and isolate the high switching noise
digital outputs from the relatively sensitive internal analog
phase–locked loop. In a controlled environment such as an
evaluation board this level of isolation is sufficient. However,
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 simplest form of isolation is a
power supply filter on the VCCA pin for the MPC953.
The MPC953 is most susceptible to noise with spectral
content in the 100KHz to 10MHz 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 that will be seen between the V CC supply and the VCCA
pin of the MPC953. From the data sheet the I VCCA current
(the current sourced through the VCCA pin) is typically 15mA
(20mA maximum), assuming that a minimum of 3.0V must be
maintained on the VCCA pin very little DC voltage drop can
be tolerated when a 3.3V V CC supply is used. The resistor
shown in Figure 3 must have a resistance of 10–15 to meet
the voltage drop criteria. The RC filter pictured will provide a
broadband filter with approximately 100:1 attenuation for
noise whose spectral content is above 20KHz. As the noise
frequency crosses the series resonant point of an individual
capacitor it’s 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. It is recommended that the user start
with an 8–10 resistor to avoid potential V CC drop problems
and only move to the higher value resistors when a higher
level of attenuation is shown to be needed.
minimize the susceptibility to power supply noise (isolated
power and grounds and fully differential PLL) there still may
MPC953
MOTOROLA
The MPC953 is a mixed analog/digital product and as
Figure 3 illustrates a typical power supply filter scheme.
Although the MPC953 has several design features to
MPC953
Figure 3. Power Supply Filter
VCCA
VCC
0.01 F
R S =5–15
22 F
0.01 F
3.3V
4
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.
Driving Transmission Lines
speed signals in a terminated transmission line environment.
To provide the optimum flexibility to the user the output
drivers were designed to exhibit the lowest impedance
possible. With an output impedance of approximately 20
the drivers can drive either parallel or series terminated
transmission lines. For more information on transmission
lines the reader is referred to application note AN1091 in the
Timing Solutions brochure (BR1333/D).
distribution of signals is the method of choice. In a
point–to–point scheme either series terminated or parallel
terminated transmission lines can be used. The parallel
technique terminates the signal at the end of the line with a
50
level of DC current and thus only a single terminated line can
be driven by each output of the MPC953 clock driver. For the
series terminated case however there is no DC current draw,
thus the outputs can drive multiple series terminated lines.
Figure 4 illustrates an output driving a single series
terminated line vs two series terminated lines in parallel.
When taken to its extreme the fanout of the MPC953 clock
driver is effectively doubled due to its capability to drive
multiple lines.
results of an output driving a single line vs two lines. In both
cases the drive capability of the MPC953 output buffers is
more than sufficient to drive 50
incident edge. Note from the delay measurements in the
simulations a delta of only 43ps exists between the two
differently loaded outputs. This suggests that the dual line
driving need not be used exclusively to maintain the tight
output–to–output skew of the MPC953. The output waveform
in Figure 5 shows a step in the waveform, this step is caused
IN
IN
The MPC953 clock driver was designed to drive high
In most high performance clock networks point–to–point
The waveform plots of Figure 5 show the simulation
Figure 4. Single versus Dual Transmission Lines
resistance to VCC/2. This technique draws a fairly high
OUTPUT
OUTPUT
BUFFER
MPC953
BUFFER
MPC953
14
14
R S = 36
R S = 36
R S = 36
transmission lines on the
Z O = 50
Z O = 50
Z O = 50
TIMING SOLUTIONS
OutA
OutB0
OutB1