MPC9658 REVISION 6 JANUARY 8, 2013 6 ©2013 Integrated Device Technology, Inc.
MPC9658 Data Sheet 3.3V 1:10 LVCMOS PLL CLOCK GENERATOR
APPLICATIONS INFORMATION
Programming the MPC9658
The MPC9658 supports output clock frequencies from 50
to 250 MHz. Two different feedback divider configurations
can be used to achieve the desired frequency operation
range. The feedback divider (VCO_SEL) should be used to
situate the VCO in the frequency lock range between 200 and
500 MHz for stable and optimal operation. Two operating
frequency ranges are supported: 50 to 125 MHz and 100 to
250 MHz. Table 7. MPC9658 Configurations (QFB connected
to FB_IN) illustrates the configurations supported by the
MPC9658. PLL zero-delay is supported if BYPASS
=1,
PLL_EN = 1, and the input frequency is within the specified
PLL reference frequency range.
Power Supply Filtering
The MPC9658 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 V
CCA_PLL
power supply impacts the device
characteristics, for instance I/O jitter. The MPC9658 provides
separate power supplies for the output buffers (V
CC
) and the
phase-locked loop (V
CCA_PLL
) 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
V
CC_PLL
pin for the MPC9658. Figure 3 illustrates a typical
power supply filter scheme. The MPC9658 frequency and
phase stability is most susceptible to noise with spectral
content in the 100 kHz to 20 MHz 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 R
F
. From the data sheet
the I
CC_PLL
current (the current sourced through the
V
CC_PLL
pin) is typically 12 mA (20 mA maximum), assuming
that a minimum of 2.835 V must be maintained on the
V
CC_PLL
pin.
Figure 3. V
CC_PLL
Power Supply Filter
The minimum values for R
F
and the filter capacitor C
F
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 3, the filter cut-off frequency is around
3
– 5 kHz and the noise attenuation at 100 kHz is better than
42 dB.
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 MPC9658 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.
Using the MPC9658 in Zero-Delay Applications
Nested clock trees are typical applications for the
MPC9658. Designs using the MPC9658 as LVCMOS PLL
fanout buffer with zero insertion delay will show significantly
lower clock skew than clock distributions developed from
CMOS fanout buffers. The external feedback option of the
MPC9658 clock driver allows for its use as a zero delay
buffer. The PLL aligns the feedback clock output edge with
the clock input reference edge resulting a near zero delay
through the device (the propagation delay through the device
is virtually eliminated). The maximum insertion delay of the
device in zero-delay applications is measured between the
reference clock input and any output. This effective delay
consists of the static phase offset, I/O jitter (phase or
long-term jitter), feedback path delay and the
output-to-output skew error relative to the feedback output.
Table 7. MPC9658 Configurations (QFB connected to FB_IN)
BYPASS PLL_EN VCO_SEL Operation
Frequency
Ratio
Output range (f
Q0–9
)
VCO
0 X X Test mode: PLL and divider bypass f
Q0–9
= f
REF
0 – 250 MHz n/a
1 0 0 Test mode: PLL bypass f
Q0–9
= f
REF
2 0 – 125 MHz n/a
1 0 1 Test mode: PLL bypass f
Q0–9
= f
REF
4 0 – 62.5 MHz n/a
1 1 0 PLL mode (high frequency range) f
Q0–9
= f
REF
100 – 250 MHz f
VCO
= f
REF
2
1 1 1 PLL mode (low frequency range) f
Q0–9
= f
REF
50 – 125 MHz f
VCO
= f
REF
4
V
CC_PLL
V
CC
MPC9658
10 nF
R
F
= 5–15 C
F
= 22F
C
F
33...100 nF
R
F
V
CC
