MPC9120SD 데이터 시트보기 (PDF) - Motorola => Freescale
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MPC9120SD Datasheet PDF : 6 Pages
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MPC9120
APPLICATIONS INFORMATION
Output Series Termination
With typical MPC9120 edge rates of 1.5V/ns, a PCB trace
becomes a transmission line when it is over 1–inch in length.
This transmission line needs some sort of termination
scheme to ensure good signal integrity at the load (device
receiving clock signal). Most motherboards use the practice
of series termination. In series termination, a series
termination resistor (external resistor) is added in series with
the driver device output, as shown in Figure 3, series
termination resistor value is chosen so that its value, added
to the output impedance of the driver, is equal to the PCB
trace impedance, or in other words, RTH = RS + ZL. The
series termination resistor must be located close to the
device output.
Typical system PCB trace impedance is 50–70Ω, which is
low enough to produce sufficient signal rise and fall time at
the load capacitance presented by a standard CMOS input.
Figure 4 illustrates proper series termination of the 15Ω
MPC9120 output driving a 60Ω transmission line.
RTH
Output Buffer Model
RS
Series
Termination
Resistor
ZL
Transmission Line
(PCB Clock Trace)
Figure 3. Clock Output Series Termination
15Ω
Output Buffer Model
45Ω
Series
Termination
Resistor
60Ω
Transmission Line
(PCB Clock Trace)
Figure 4. Clock Output Series Termination
Voltage
(V)
0
1.000
1.400
1.500
1.650
1.800
2.000
2.400
2.600
3.135
3.300
3.465
Pull–Up
Imin
(mA)
Ityp
(mA)
–72
–116
–72
–116
–68
–110
–67
–107
–64
–103
–60
–98
–54
–90
–39
–69
–30
–56
0
–15
–
0
–
–
Imax
(mA)
–198
–198
–188
–184
–177
–170
–157
–126
–107
–46
–23
0
Voltage
(V)
0
0.400
0.650
0.850
1.000
1.400
1.500
1.650
1.800
1.950
3.315
3.600
Pull–Down
Imin
(mA)
Ityp
(mA)
0
0
23
34
35
52
43
65
49
74
61
93
64
98
67
103
70
108
72
112
72
112
–
112
Figure 5. Typical Output V/I Characteristics for MPC9120
Imax
(mA)
0
53
83
104
118
152
159
168
177
184
204
204
TIMING SOLUTIONS
5
BR1333 — REV 5
MOTOROLA
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