MPC93R51 REVISION 4 JANUARY 31, 2013
7
2013 Integrated Device Technology, Inc.
MPC93R51 Data Sheet
LOW VOLTAGE PLL CLOCK DRIVER
Figure 3. MPC93R51 Zero-Delay Configuration
(Feedback of QD4)
Calculation of Part-to-Part Skew
The MPC93R51 zero delay buffer supports applications
where critical clock signal timing can be maintained across
several devices. If the reference clock inputs (TCLK or PCLK)
of two or more MPC93R51 are connected together, the
maximum overall timing uncertainty from the common TCLK
input to any output is:
tSK(PP) = t() + tSK(O) + tPD, LINE(FB) + tJIT() CF
This maximum timing uncertainty consists of 4
components: static phase offset, output skew, feedback
board trace delay and I/O (phase) jitter.
Figure 4. MPC93R51 Max. Device-to-Device Skew
Due to the statistical nature of I/O jitter, a RMS value (1
)
is specified. I/O jitter numbers for other confidence factors
The feedback trace delay is determined by the board
layout and can be used to fine-tune the effective delay
through each device. In the following example calculation, an
I/O jitter confidence factor of 99.7% (
3) is assumed,
resulting in a worst case timing uncertainty from input to any
output of –251 ps to 351 ps relative to TCLK (VCC = 3.3 V and
fVCO = 400 MHz):
tSK(PP) = [-50ps...150ps] + [-150ps...150ps] +
[(17ps –3)...(17ps 3)] + tPD, LINE(FB)
tSK(PP) = [-251ps...351ps] + tPD, LINE(FB)
Above equation uses the maximum I/O jitter number
shown in the AC characteristic table for VCC = 3.3 V (17 ps
RMS). I/O jitter is frequency dependent with a maximum at
the lowest VCO frequency (200 MHz for the MPC93R51).
Applications using a higher VCO frequency exhibit less I/O
jitter than the AC characteristic limit. The I/O jitter
characteristics in
Figure 5 can be used to derive a smaller
I/O jitter number at the specific VCO frequency, resulting in
tighter timing limits in zero-delay mode and for part-to-part
skew tSK(PP).
Figure 5. Max. I/O Jitter (RMS) Versus Frequency
for VCC = 3.3 V
Power Supply Filtering
The MPC93R51 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.
Noise on the VCCA (PLL) power supply impacts the device
characteristics, for instance, I/O jitter. The MPC93R51
provides separate power supplies for the output buffers (VCC)
and the phase-locked loop (VCCA) 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
Table 8. Confidence Factor CF
CF
Probability of clock edge within the distribution
MPC93R51
TCLK
QA
fref = 100 MHz
REF_SEL
PLL_EN
FSELA
FSELB
FSELC
FSELD
Ext_FB
QB
QC0
QC1
QD0
QD1
QD2
QD3
QD4
2 x 100 MHz
4 x 100 MHz
100 MHz (Feedback)
1
0
tPD,LINE(FB)
tJIT()
+tSK(O)
—t(
+t()
tJIT()
+tSK(O)
tSK(PP)
Max. skew
TCLKCommon
QFBDevice 1
Any QDevice 1
QFBDevice2
Any QDevice 2
1
0.68268948
2
0.95449988
3
0.99730007
4
0.99993663
5
0.99999943
6
0.99999999
Table 8. Confidence Factor CF
30
25
20
15
10
5
0
75
225
250
275
300
325
VCO frequency [MHz]
t JIT(
)[p
s]
ms
Max. I/O Jitter versus frequency
350
375
400