MPC974FA Freescale Semiconductor, MPC974FA Datasheet - Page 5

• Manufacturer Part Number: MPC974FA
• Description: IC PLL CLOCK DRIVER 52-LQFP
• Manufacturer: Freescale Semiconductor
• Type: Clock Driver, Fanout Distribution, Multiplexerr

Specifications of MPC974FA

• Pll: Yes with Bypass
• Input: LVCMOS, LVTTL
• Output: LVCMOS
• Number Of Circuits: 1
• Ratio - Input:output: 2:14
• Differential - Input:output: No/No
• Frequency - Max: 125MHz
• Divider/multiplier: Yes/Yes
• Voltage - Supply: 3.135 V ~ 3.465 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 52-LQFP
• Frequency-max: 125MHz
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Power Supply Filtering
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 MPC974 provides separate
power supplies for the output buffers (V CCO ) and the internal
PLL (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 MPC974.
TIMING SOLUTIONS
BR1333 — Rev 6
The MPC974 is a mixed analog/digital product and
33MHz
25MHz
fsela
fsela
0
0
Figure 4. Power Supply Filter
MPC974
fselb
fselb
VCCA
0
1
VCC
33MHz
25MHz
TCLK
FB_In
TCLK
FB_In
fselc
fselc
0
1
QFB
QFB
0.01 F
fselFB
fselFB
Qa
Qb
Qa
Qb
Qc
Qc
00
01
R S =5–15
22 F
5
5
4
5
5
4
VCO_Sel
VCO_Sel
Figure 3. MPC974 Programming Schemes
0
0
0.01 F
3.3V
66MHz
66MHz
33MHz
100MHz
50MHz
33MHz
5
The MPC974 is most susceptible to noise with spectral
content in the 1KHz to 1MHz 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 MPC974. 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 4 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.
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.
Figure 4 illustrates a typical power supply filter scheme.
Although the MPC974 has several design features to
33MHz
50MHz
fsela
fsela
0
1
fselb
fselb
33MHz
1
50MHz
1
TCLK
FB_In
TCLK
FB_In
fselc
fselc
1
0
QFB
QFB
fselFB
fselFB
Qa
Qb
Qc
Qa
Qb
Qc
10
00
5
5
4
5
5
4
VCO_Sel
VCO_Sel
0
0
100MHz
50MHz
33MHz
50MHz
50MHz
50MHz
MPC974
MOTOROLA