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參數(shù)資料
| 型號(hào)： | LMH6715 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Dual Wideband Video Op Amp |
| 中文描述： | 雙寬帶視頻運(yùn)算放大器 |
| 文件頁(yè)數(shù)： | 9/12頁(yè) |
| 文件大?。?/td> | 484K |
| 代理商： | LMH6715 |
Application Introduction
(Continued)
R
F
vs. Non-Inverting Gain
20042921
Both plots show the value of R
approaching a minimum
value (dashed line) at high gains. Reducing the feedback
resistor below this value will result in instability and possibly
oscillation. The recommended value of R
is depicted by the
solid line, which begins to increase at higher gains. The
reason that a higher R
is required at higher gains is the
need to keep R
from decreasing too far below the output
impedance of the input buffer. For the LMH6715 the output
resistance of the input buffer is approximately 160
and 50
is a practical lower limit for R
. Due to the limitations on R
G
the LMH6715 begins to operate in a gain bandwidth limited
fashion for gains of
±
5V/V or greater.
R
F
vs. Inverting Gain
20042922
When using the LMH6715 as a replacement for the CLC412,
identical bandwidth can be obtained by using an appropriate
value of R
F
. The chart “Frequency Response vs. R
” shows
that an R
of approximately 700
will provide bandwidth
very close to that of the CLC412. At other gains a similar
increase in R
F
can be used to match the new and old parts.
CIRCUIT LAYOUT
With all high frequency devices, board layouts with stray
capacitances have a strong influence over AC performance.
The LMH6715 is no exception and its input and output pins
are particularly sensitive to the coupling of parasitic capaci-
tances (to AC ground) arising from traces or pads placed too
closely (
<
0.1”) to power or ground planes. In some cases,
due to the frequency response peaking caused by these
parasitics, a small adjustment of the feedback resistor value
will serve to compensate the frequency response. Also, it is
very important to keep the parasitic capacitance across the
feedback resistor to an absolute minimum.
The performance plots in the data sheet can be reproduced
using the evaluation boards available from National. The
CLC730036 board uses all SMT parts for the evaluation of
the LMH6715. The board can serve as an example layout for
the final production printed circuit board.
Care must also be taken with the LMH6715’s layout in order
to achieve the best circuit performance, particularly channel-
to-channel isolation. The decoupling capacitors (both tanta-
lum and ceramic) must be chosen with good high frequency
characteristics to decouple the power supplies and the
physical placement of the LMH6715’s external components
is critical. Grouping each amplifier’s external components
with their own ground connection and separating them from
the external components of the opposing channel with the
maximum possible distance is recommended. The input
(R
) and gain setting resistors (R
) are the most critical. It is
also recommended that the ceramic decoupling capacitor
(0.1μF chip or radial-leaded with low ESR) should be placed
as closely to the power pins as possible.
POWER DISSIPATION
Follow these steps to determine the Maximum power dissi-
pation for the LMH6715:
1. Calculate the quiescent (no-load) power: P
AMP
= I
CC
(V
CC
- V
EE
)
2. Calculate the RMS power at the output stage: P
O
= (V
CC
-V
LOAD
)(I
LOAD
), where V
LOAD
and I
LOAD
are the voltage and
current across the external load.
3. Calculate the total RMS power: Pt = P
AMP
+ P
O
The maximum power that the LMH6715, package can dissi-
pate at a given temperature can be derived with the following
equation:
Pmax = (150
o
- Tamb)/
θ
JA
, where Tamb = Ambient tempera-
ture (C) and
θ
= Thermal resistance, from junction to
ambient, for a given package (C/W). For the SOIC package
θ
JA
is 145C/W.
MATCHING PERFORMANCE
With proper board layout, the AC performance match be-
tween the two LMH6715’s amplifiers can be tightly controlled
as shown in Typical Performance plot labeled “Small-Signal
Channel Matching”.
The measurements were performed with SMT components
using a feedback resistor of 300
at a gain of +2V/V.
The LMH6715’s amplifiers, built on the same die, provide the
advantage of having tightly matched DC characteristics.
SLEW RATE AND SETTLING TIME
One of the advantages of current-feedback topology is an
inherently high slew rate which produces a wider full power
bandwidth. The LMH6715 has a typical slew rate of 1300V/
μs. The required slew rate for a design can be calculated by
the following equation: SR = 2
π
fV
pk
.
Careful attention to parasitic capacitances is critical to
achieving the best settling time performance. The LMH6715
L
www.national.com
9
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| LMH6715JFQML | 制造商:Texas Instruments 功能描述: |
| LMH6715JFQMLV | 功能描述:運(yùn)算放大器 - 運(yùn)放 RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補(bǔ)償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LMH6715J-QML | 功能描述:運(yùn)算放大器 - 運(yùn)放 RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補(bǔ)償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LMH6715MA | 功能描述:運(yùn)算放大器 - 運(yùn)放 RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補(bǔ)償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LMH6715MA/NOPB | 功能描述:運(yùn)算放大器 - 運(yùn)放 RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補(bǔ)償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
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