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參數(shù)資料
| 型號： | LMH6640 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | TFT-LCD Single, 16V Rail-to-Rail High Output Operational Amplifier |
| 中文描述： | TFT - LCD的單，16V的軌到軌輸出運算放大器高 |
| 文件頁數(shù)： | 11/13頁 |
| 文件大小： | 901K |
| 代理商： | LMH6640 |
Typical Performance Characteristics
At T
J
= 25C, V
+
= 16 V, V
= 0V, R
F
= 330
for A
V
= +2, R
F
=
1 k
for A
V
= 1. R
L
tied to V
+
/2. Unless otherwise specified. (Continued)
Differential Gain/Phase vs. IRE
20086225
Application Notes
With its high output current and speed, one of the major
applications for the LMH6640 is the V
COM
driver in a TFT
panel. This application is a specially taxing one because of
the demands it places on the operational amplifier’s output to
drive a large amount of bi-directional current into a heavy
capacitive load while operating under unity gain condition,
which is a difficult challenge due to loop stability reasons.
For a more detailed explanation of what a TFT panel is and
what its amplifier requirements are, please see the Applica-
tion Notes section of the LM6584 found on the web at:
http://www.national.com/ds.cgi/LM/LM6584.pdf
Because of the complexity of the TFT V
waveform and
the wide variation in characteristics between different TFT
panels, it is difficult to decipher the results of circuit testing in
an actual panel. The ability to make simplifying assumptions
about the load in order to test the amplifier on the bench
allows testing using standard equipment and provides famil-
iar results which could be interpreted using standard loop
analysis techniques. This is what has been done in this
application note with regard to the LMH6640’s performance
when subjected to the conditions found in a TFT V
COM
application.
Figure 1
, shows a typical simplified V
application with
the LMH6640 buffering the V
potential (which is usually
around
simplified model of the load. The load represents the cumu-
lative effect of all stray capacitances between the V
COM
node and both row and column lines. Associated with the
capacitances shown, is the distributed resistance of the lines
to each individual transistor switch. The other end of this R-C
ladder is driven by the column driver in an actual panel and
here is driven with a low impedance MOSFET driver (labeled
“High Current Driver”) for the purposes of this bench test to
simulate the effect that the column driver exerts on the V
COM
load.
The modeled TFT V
load, shown in
Figure 1
, is based on
the following simplifying assumptions in order to allow for
easy bench testing and yet allow good matching results
obtained in the actual application:
1
2
of panel supply voltage) and looking into the
The sum of all the capacitors and resistors in the R-C
ladder is the total V
COM
capacitance and resistance re-
spectively. This total varies from panel to panel; capaci-
tance could range from 50 nF-200 nF and the resistance
could be anywhere from 20
-100
.
The number of ladder sections has been reduced to a
number (4 sections in this case) which can easily be put
together in the lab and which behaves reasonably close
to the actual load.
In this example, the LMH6640 was tested under the simu-
lated conditions of total 209 nF capacitance and 54
as
shown in
Figure 1
.
R
S
is sometimes used in the panel to provide additional
isolation from the load while R
F2
provides a more direct
feedback from the V
COM
. R
F1
, R
F2
, and R
S
are trimmed in
the actual circuit with settling time and stability trade-offs
considered and evaluated. When tested under simulated
load conditions of
Figure 1
, here are the resultant voltage
and current waveforms at the LMH6640 output:
20086235
FIGURE 1. LMH6640 in a V
Buffer Application with
Simulated TFT Load
L
www.national.com
11
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LMH6640MF | 功能描述:運算放大器 - 運放 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 |
| LMH6640MF/NOPB | 功能描述:運算放大器 - 運放 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 |
| LMH6640MF/NOPB | 制造商:Texas Instruments 功能描述:Operational Amplifier (Op-Amp) IC |
| LMH6640MFX | 功能描述:運算放大器 - 運放 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 |
| LMH6640MFX/NOPB | 功能描述:運算放大器 - 運放 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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