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参数资料
| 型号： | LMH6734MQX/NOPB |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 音频／视频放大 |
| 英文描述： | 3 CHANNEL, VIDEO AMPLIFIER, PDSO16 |
| 封装： | ROHS COMPLIANT, SSOP-16 |
| 文件页数： | 7/18页 |
| 文件大小： | 561K |
| 代理商： | LMH6734MQX/NOPB |
30003666
FIGURE 12. Frequency Response vs. Normalized Gain and CAT5 Cable Length
DRIVING CAPACITIVE LOADS
Capacitive output loading applications will benefit from the
use of a series output resistor R
OUT. Figure 13 shows the use
of a series output resistor, R
OUT, to stabilize the amplifier out-
put under capacitive loading. Capacitive loads of 5 to 120 pF
are the most critical, causing ringing, frequency response
peaking and possible oscillation. The charts “Suggested
R
OUT vs. Cap Load” give a recommended value for selecting
a series output resistor for mitigating capacitive loads. The
values suggested in the charts are selected for 0.5 dB or less
of peaking in the frequency response. This gives a good com-
promise between settling time and bandwidth. For applica-
tions where maximum frequency response is needed and
some peaking is tolerable, the value of R
OUT can be reduced
slightly from the recommended values.
30003638
FIGURE 13. Decoupling Capacitive Loads
LAYOUT CONSIDERATIONS
Whenever questions about layout arise, use the evaluation
board as a guide. The LMH730275 is the evaluation board
supplied with samples of the LMH6734.
To reduce parasitic capacitances, ground and power planes
should be removed near the input and output pins. For long
signal paths controlled impedance lines should be used,
along with impedance matching elements at both ends.
Bypass capacitors should be placed as close to the device as
possible. Bypass capacitors from each rail to ground are ap-
plied in pairs. The larger electrolytic bypass capacitors can be
located farther from the device, the smaller ceramic capaci-
tors should be placed as close to the device as possible. The
LMH6734 has multiple power and ground pins for enhanced
supply bypassing. Every pin should ideally have a separate
bypass capacitor. Sharing bypass capacitors may slightly de-
grade second order harmonic performance, especially if the
Figure 3 it is recommended an optional capacitor, C
SS= 0.01
μF, be connected between the split supplies for best second
harmonic distortion. Another option to using C
SS is to use
pairs of 0.01
μF and 0.1 μF ceramic capacitors for each supply
bypass.
VIDEO PERFORMANCE
The LMH6734 has been designed to provide excellent per-
formance with production quality video signals in a wide va-
riety of formats such as HDTV and High Resolution VGA.
NTSC and PAL performance is nearly flawless. Best perfor-
mance will be obtained with back terminated loads. The back
termination reduces reflections from the transmission line and
effectively masks transmission line and other parasitic ca-
pacitances from the amplifier output stage. Figure 7 shows a
typical configuration for driving a 75
cable. The amplifier is
configured for a gain of two to make up for the 6 dB of loss in
R
OUT.
POWER DISSIPATION
The LMH6734 is optimized for maximum speed and perfor-
mance in the small form factor of the standard SSOP-16
package. To achieve its high level of performance, the
LMH6734 consumes an appreciable amount of quiescent
current which cannot be neglected when considering the total
package power dissipation limit. The quiescent current con-
tributes to about 40° C rise in junction temperature when no
additional heat sink is used (V
S = ±5V, all three channels on).
Therefore, it is easy to see the need for proper precautions in
order to make sure the junction temperature’s absolute max-
imum rating of 150°C is not violated.
To ensure maximum output drive and highest performance,
thermal shutdown is not provided. Therefore, it is of utmost
importance to make sure that the T
JMAX is never exceeded
due to the overall power dissipation (all three channels).
With the LMH6734 used in a back-terminated 75
RGB ana-
log video system (with 2 V
PP output voltage), the total power
dissipation is around 305 mW of which 220 mW is due to the
quiescent device dissipation (output black level at 0V). With
no additional heat sink used, the junction temperature rises
to about 120° C when operated at 85°C ambient.
To reduce the junction temperature many options are avail-
able. Forced air cooling is the easiest option. An external add-
15
www.national.com
LMH6734
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LMH6738 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Very Wideband, Low Distortion Triple Op Amp |
| LMH6738MQ | 功能描述:运算放大器 - 运放 RoHS:否 制造商:STMicroelectronics 通道数量:4 共模抑制比（最小值）:63 dB 输入补偿电压:1 mV 输入偏流（最大值）:10 pA 工作电源电压:2.7 V to 5.5 V 安装风格:SMD/SMT 封装 / 箱体:QFN-16 转换速度:0.89 V/us 关闭:No 输出电流:55 mA 最大工作温度:+ 125 C 封装:Reel |
| LMH6738MQ/NOPB | 功能描述:运算放大器 - 运放 Triple Video Op-Amp RoHS:否 制造商:STMicroelectronics 通道数量:4 共模抑制比（最小值）:63 dB 输入补偿电压:1 mV 输入偏流（最大值）:10 pA 工作电源电压:2.7 V to 5.5 V 安装风格:SMD/SMT 封装 / 箱体:QFN-16 转换速度:0.89 V/us 关闭:No 输出电流:55 mA 最大工作温度:+ 125 C 封装:Reel |
| LMH6738MQX | 功能描述:运算放大器 - 运放 RoHS:否 制造商:STMicroelectronics 通道数量:4 共模抑制比（最小值）:63 dB 输入补偿电压:1 mV 输入偏流（最大值）:10 pA 工作电源电压:2.7 V to 5.5 V 安装风格:SMD/SMT 封装 / 箱体:QFN-16 转换速度:0.89 V/us 关闭:No 输出电流:55 mA 最大工作温度:+ 125 C 封装:Reel |
| LMH6738MQX/NOPB | 功能描述:运算放大器 - 运放 RoHS:否 制造商:STMicroelectronics 通道数量:4 共模抑制比（最小值）:63 dB 输入补偿电压:1 mV 输入偏流（最大值）:10 pA 工作电源电压:2.7 V to 5.5 V 安装风格:SMD/SMT 封装 / 箱体:QFN-16 转换速度:0.89 V/us 关闭:No 输出电流:55 mA 最大工作温度:+ 125 C 封装:Reel |
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