MPC951
MOTOROLA
TIMING SOLUTIONS
4
PLL INPUT REFERENCE CHARACTERISTICS (TA = 0 to 70°C)
Symbol
Characteristic
Min
Max
Unit
Condition
tr, tf
TCLK Input Rise/Falls
3.0
ns
fref
Reference Input Frequency
100
MHz
Note 1.
frefDC
Reference Input Duty Cycle
25
75
%
1. Maximum and minimum input reference is limited by the VCO lock range and the feedback divider for the TCLK or PECL_CLK inputs.
AC CHARACTERISTICS (TA = 0°C to 70°C, VCC = 3.3V ±5%)
Symbol
Characteristic
Min
Typ
Max
Unit
Condition
tr, tf
Output Rise/Fall Time
0.10
1.0
ns
0.8 to 2.0V, Note 4.
tpw
Output Duty Cycle
tCYCLE/2–1000
tCYCLE/2+1000
ps
Note 4.
tsk(O)
Output–to–Output Skews
Same Frequencies
200
375
ps
Note 4.
Different Frequencies
Qafmax < 150MHz
Qafmax > 150MHz
325
500
750
fVCO
PLL VCO Lock Range
200
480
MHz
Note 3.
fmax
Maximum Output
Qa (
÷2)
Frequency
Qa/Qb (
÷4)
Qb (
÷8)
180
120
60
MHz
Note 4.
tpd
Input to Ext_FB Delay
TCLK
(Note 1.)
PECL_CLK
50
–950
250
–770
400
–600
ps
fref = 50MHz
Feedback=VCO/8
Note 4.
tPLZ,HZ
Output Disable Time
7
ns
Note 4.
tPZL
Output Enable Time
6
ns
Note 4.
tjitter
Cycle–to–Cycle Jitter (Peak–to–Peak)
±100
ps
Note 2.
tlock
Maximum PLL Lock Time
10
ms
1. The tpd window is specified for a 50Mhz input reference clock. The window will enlarge/reduce proportionally from the minimum limits with an
increase/decrease of the input reference clock period. The tpd does not include jitter.
2. See Applications Info section for more jitter information.
3. The PLL will be unstable with a divide by 2 feedback ratio.
4. Termination of 50
W to VCC/2.
APPLICATIONS INFORMATION
Programming the MPC951
The MPC951 clock driver outputs can be configured into
several frequency relationships. The output dividers for the
four output groups allows the user to configure the outputs
into 1:1, 2:1, 4:1 and 4:2:1 frequency ratios. The use of even
dividers ensures that the output duty cycle is always 50%.
Table 1 illustrates the various output configurations, the table
describes the outputs using the VCO frequency as a
reference. As an example for a 4:2:1 relationship the Qa
outputs would be set at VCO/2, the Qb’s and Qc’s at VCO/4
and the Qd’s at VCO/8. These settings will provide output
frequencies with a 4:2:1 relationship.
The division settings establish the output relationship, but
one must still ensure that the VCO will be stable given the
frequency of the outputs desired. The feedback frequency
should be used to situate the VCO into a frequency range in
which the PLL will be stable. The design of the PLL is such
that for output frequencies between 25 and 180MHz the
MPC951 can generally be configured into a stable region.
The relationship between the input reference and the
output frequency is also very flexible. Table 1 can be used to
determine the multiplication factor, there are too many
potential combinations to tabularize the external feedback
condition. Figure 1 through Figure 2 illustrates several
programming possibilities, although not exhaustive it is
representative of the potential applications.
MPC951
Low Voltage PLL Clock Driver
NETCOM
IDT Low Voltage PLL Clock Driver
Freescale Timing Solutions Organization has been acquired by Integrated Device Technology, Inc
MPC951
4