mpc970 Freescale Semiconductor, Inc, mpc970 Datasheet - Page 9

• Manufacturer Part Number: mpc970
• Description: Low Voltage Pll Clock Driver
• Manufacturer: Freescale Semiconductor, Inc

output divide ratio. If the VCO_Sel pin is “LOW” the
multiplication factor will be reduced further by 2. (See “Using
the On–Board Crystal Oscillator” section of this datasheet.)
Using the External Feedback Feature of the MPC970/71
waveforms and the input waveforms are critical the external
feedback option will likely be used. Table 1 and Table 2 are
still appropriate for establishing the potential output
frequency relationships. The input reference frequency for
external feedback applications will be equal to the frequency
of the feedback signal. As a result the use of the external
feedback yields a number of potential input to output
frequency multiplication factors which are not available using
the internal feedback. Using the external feedback the device
can function as a zero delay buffer and could multiply the
input from 4 to as much as 48. In practice however the
multiplication factor is limited by the loop dynamics of the
PLL. The MPC970 PLL was optimized for an input reference
frequency or greater than 10MHz. Frequencies lower than
10MHz will tend to pass through the filter and add jitter to the
PLL. In addition the PLL was optimized for feedback divide
ratios of between 8 and 64. The user should avoid using the
device with feedback divide ratios outside of this range. For
the external feedback case the feedback divide ratio will
include the 2 (if VCO_Sel is LOW) plus the output divider for
* BCLK_En output is delayed relative to other outputs
TIMING SOLUTIONS
BR1333 — Rev 6
Table 1. Programmable Output Frequency Relationships (MPC601_Clks = ‘HIGH’; VCO_Sel = ‘HIGH’)
PCI_Div1
In applications where the relationship between the output
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
PCI_Div0
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
INPUTS
BCLK_Div1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
BCLK_Div0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
2x_PCLK
VCO/2
VCO/2
VCO/2
VCO/2
VCO/2
VCO/2
VCO/2
VCO/2
VCO/2
VCO/2
VCO/2
VCO/2
VCO/2
VCO/2
VCO/2
VCO/2
9
the feedback output. If, for instance the MPC970 is to be
used as a zero delay buffer the VCO_Sel pin should be pulled
LOW and all of the outputs should be set in a VCO/4 mode.
This would produce a feedback ratio of 8. Several potential
configurations using the external feedback are pictured in
Figure 4 through Figure 7.
applications in which more than one clock driver need to be
synchronized. The external feedback option ensures that the
feed through delay is the same as the feedback delay. This
functionality removes propagation delay variation as a factor
in the determination of part to part skew. The low jitter PLL
used in the MPC970 has a near zero deadband phase
detector and very little part to part variability. The result is a
very low phase error variability in the product. When coupled
with the output to output skew the phase error variability
accounts for the part to part skew of the device. From the
specification table one sees that the worst case part to part
skew of the device is 800ps, assuming that there is zero
skew in the multiple reference inputs. For multiple MPC970
applications if the lowest generated output frequency is used
as the feedback signal the devices will be guaranteed to be
synchronized. For applications where the lowest frequency is
not used as the reference or where the internal feedback is
used there is no way to guarantee that the multiple devices
will be phase synchronized.
The external feedback option of the MPC970 is critical for
PCLKEN
VCO/4
VCO/4
VCO/4
VCO/4
VCO/4
VCO/4
VCO/4
VCO/4
VCO/4
VCO/4
VCO/4
VCO/4
VCO/4
VCO/4
VCO/4
VCO/4
OUTPUTS
BCLKEN*
VCO/12
VCO/16
VCO/12
VCO/16
VCO/12
VCO/16
VCO/12
VCO/16
VCO/4
VCO/8
VCO/4
VCO/8
VCO/4
VCO/8
VCO/4
VCO/8
VCO/12
VCO/16
VCO/12
VCO/16
VCO/12
VCO/16
VCO/12
VCO/16
VCO/4
VCO/8
VCO/4
VCO/8
VCO/4
VCO/8
VCO/4
VCO/8
BCLK
MPC970
MOTOROLA
PCI_CLK
VCO/12
VCO/16
VCO/16
VCO/24
VCO/32
VCO/12
VCO/24
VCO/36
VCO/48
VCO/4
VCO/8
VCO/8
VCO/4
VCO/4
VCO/4
VCO/4