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| 型号： | MPC9443AE |
| 厂商： | FREESCALE SEMICONDUCTOR INC |
| 元件分类： | 时钟及定时 |
| 英文描述： | 9443 SERIES, LOW SKEW CLOCK DRIVER, 16 TRUE OUTPUT(S), 0 INVERTED OUTPUT(S), PQFP48 |
| 封装： | 7 X 7 MM, PLASTIC, LQFP-48 |
| 文件页数： | 11/12页 |
| 文件大小： | 209K |
| 代理商： | MPC9443AE |
MPC9443
FREESCALE SEMICONDUCTOR ADVANCED CLOCK DRIVERS DEVICE DATA
599
APPLICATIONS INFORMATION
Driving Transmission Lines
The MPC9443 clock driver was designed to drive high speed
signals in a terminated transmission line environment. To
provide the optimum flexibility to the user the output drivers
were designed to exhibit the lowest impedance possible. With
an output impedance of less than 20
the drivers can drive
either parallel or series terminated transmission lines at
VCC = 3.3 V. For more information on transmission lines the
reader is referred to application note AN1091. In most high
performance clock networks point-to-point distribution of
signals is the method of choice. In a point-to-point scheme
either series terminated or parallel terminated transmission
lines can be used. The parallel technique terminates the signal
at the end of the line with a 50
resistance to V
CC÷2.
This technique draws a fairly high level of DC current and
thus only a single terminated line can be driven by each output
of the MPC9443 clock driver. For the series terminated case
however there is no DC current draw, thus the outputs can drive
multiple series terminated lines. Figure 3. Single versus Dual
Transmission Lines illustrates an output driving a single series
terminated line versus two series terminated lines in parallel.
When taken to its extreme the fanout of the MPC9443 clock
driver is effectively doubled due to its capability to drive multiple
lines (at VCC = 3.3 V).
Figure 3. Single versus Dual Transmission Lines
The waveform plots in Figure 4. Single versus Dual
Waveforms show the simulation results of an output driving a
single line versus two lines. In both cases the drive capability of
the MPC9443 output buffer is more than sufficient to drive 50
transmission lines on the incident edge. Note from the delay
measurements in the simulations a delta of only 43 ps exists
between the two differently loaded outputs. This suggests that
the dual line driving need not be used exclusively to maintain
the tight output-to-output skew of the MPC9443. The output
waveform in Figure 4. Single versus Dual Waveforms shows a
step in the waveform, this step is caused by the impedance
mismatch seen looking into the driver. The parallel combination
of the 31
series resistor plus the output impedance does not
match the parallel combination of the line impedances. The
voltage wave launched down the two lines will equal:
VL = VS (Z0 ÷ (RS + R0 + Z0))
Z0 = 50 || 50
RS = 31 || 31
R0 = 19
VL = 3.0 (25 ÷ (15.5 + 19 + 25)
= 1.26V
At the load end the voltage will double, due to the near unity
reflection coefficient, to 2.52 V. It will then increment towards
the quiescent 3.0 V in steps separated by one round trip delay
(in this case 4.0 ns).
Figure 4. Single versus Dual Waveforms
Since this step is well above the threshold region it will not
cause any false clock triggering, however designers may be
uncomfortable with unwanted reflections on the line. To better
match the impedances when driving multiple lines the situation
in Figure 5. Optimized Dual Line Termination should be used. In
this case the series terminating resistors are reduced such that
when the parallel combination is added to the output buffer
impedance the line impedance is perfectly matched.
Figure 5. Optimized Dual Line Termination
19
IN
MPC9443
OUTPUT
BUFFER
RS = 31
ZO = 50
OutA
19
IN
MPC9443
OUTPUT
BUFFER
RS = 31
ZO = 50
OutB0
RS = 31
ZO = 50
OutB1
TIME (ns)
VOLTA
G
E(V)
3.0
2.5
2.0
1.5
1.0
0.5
0
2
4
6
8
10
12
14
OutB
tD = 3.9386
OutA
tD = 3.8956
In
19
MPC9443
OUTPUT
BUFFER
RS = 12
ZO = 50
RS = 12
ZO = 50
19
+ 12 || 12 = 50 || 50
25
= 25
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MPC9443AER2 | 功能描述:时钟驱动器及分配 FSL 1-16 LVCMOS Fanout Buffer RoHS:否 制造商:Micrel 乘法/除法因子:1:4 输出类型:Differential 最大输出频率:4.2 GHz 电源电压-最大: 电源电压-最小:5 V 最大工作温度:+ 85 C 封装 / 箱体:SOIC-8 封装:Reel |
| MPC9443FA | 功能描述:时钟缓冲器 2.5 3.3V 250MHz Clock Generator RoHS:否 制造商:Texas Instruments 输出端数量:5 最大输入频率:40 MHz 传播延迟（最大值）: 电源电压-最大:3.45 V 电源电压-最小:2.375 V 最大功率耗散: 最大工作温度:+ 85 C 最小工作温度:- 40 C 封装 / 箱体:LLP-24 封装:Reel |
| MPC9443FAR2 | 功能描述:时钟驱动器及分配 FSL 1-16 LVCMOS Fanout Buffer RoHS:否 制造商:Micrel 乘法/除法因子:1:4 输出类型:Differential 最大输出频率:4.2 GHz 电源电压-最大: 电源电压-最小:5 V 最大工作温度:+ 85 C 封装 / 箱体:SOIC-8 封装:Reel |
| MPC9446 | 制造商:MOTOROLA 制造商全称:Motorola, Inc 功能描述:2.5V and 3.3V LVCMOS Clock Fanout Buffer |
| MPC9446AC | 功能描述:时钟缓冲器 2.5 3.3V 275MHz Clock Generator RoHS:否 制造商:Texas Instruments 输出端数量:5 最大输入频率:40 MHz 传播延迟（最大值）: 电源电压-最大:3.45 V 电源电压-最小:2.375 V 最大功率耗散: 最大工作温度:+ 85 C 最小工作温度:- 40 C 封装 / 箱体:LLP-24 封装:Reel |
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