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參數資料
| 型號： | LMV342MAX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 運動控制電子 |
| 英文描述： | Single with Shutdown/Dual/Quad General Purpose, 2.7V, Rail-to-Rail Output, 125∑C, Operational Amplifiers |
| 中文描述： | DUAL OP-AMP, 4000 uV OFFSET-MAX, 1 MHz BAND WIDTH, PDSO8 |
| 封裝： | SOIC-8 |
| 文件頁數： | 13/17頁 |
| 文件大?。?/td> | 694K |
| 代理商： | LMV342MAX |
Application Section
LMV341/342/344
The LMV341/342/344 family of amplifiers features low volt-
age, low power, and rail-to-rail output operational amplifiers
designed for low voltage portable applications. The family is
designed using all CMOS technology. This results in an ultra
low input bias current. The LMV341 has a shutdown option,
which can be used in portable devices to increase battery
life.
A simplified schematic of the LMV341/342/344 family of
amplifiers is shown in
Figure 1
. The PMOS input differential
pair allows the input to include ground. The output of this
differential pair is connected to the Class AB turnaround
stage. This Class AB turnaround has a lower quiescent
current, compared to regular turnaround stages. This results
in lower offset, noise, and power dissipation, while slew rate
equals that of a conventional turnaround stage. The output
of the Class AB turnaround stage provides gate voltage to
the complementary common-source transistors at the output
stage. These transistors enable the device to have rail-to-rail
output.
CLASS AB TURNAROUND STAGE AMPLIFIER
This patented folded cascode stage has a combined class
AB amplifier stage, which replaces the conventional folded
cascode stage. Therefore, the class AB folded cascode
stage runs at a much lower quiescent current compared to
conventional folded cascode stages. This results in signifi-
cantly smaller offset and noise contributions. The reduced
offset and noise contributions in turn reduce the offset volt-
age level and the voltage noise level at the input of the
LMV341/342/344. Also the lower quiescent current results in
a high open-loop gain for the amplifier. The lower quiescent
current does not affect the slew rate of the amplifier nor its
ability to handle the total current swing coming from the input
stage.
The input voltage noise of the device at low frequencies,
below 1kHz, is slightly higher than devices with a BJT input
stage; However the PMOS input stage results in a much
lower input bias current and the input voltage noise drops at
frequencies above 1kHz.
SAMPLE AND HOLD CIRCUIT
The lower input bias current of the LMV341 results in a very
high input impedance. The output impedance when the de-
vice is in shutdown mode is quite high. These high imped-
ances, along with the ability of the shutdown pin to be
derived from a separate power source, make LMV341 a
good choice for sample and hold circuits. The sample clock
should be connected to the shutdown pin of the amplifier to
rapidly turn the device on or off.
Figure 2
shows the schematic of a simple sample and hold
circuit. When the sample clock is high the first amplifier is in
normal operation mode and the second amplifier acts as a
buffer. The capacitor, which appears as a load on the first
amplifier, will be charging at this time. The voltage across the
capacitor is that of the non-inverting input of the first amplifier
since it is connected as a voltage-follower. When the sample
clock is low the first amplifier is shut off, bringing the output
impedance to a high value. The high impedance of this
output, along with the very high impedance on the input of
the second amplifier, prevents the capacitor from discharg-
ing. There is very little voltage droop while the first amplifier
is in shutdown mode. The second amplifier, which is still in
normal operation mode and is connected as a voltage fol-
lower, also provides the voltage sampled on the capacitor at
its output.
SHUTDOWN FEATURE
The LMV341 is capable of being turned off in order to
conserve power and increase battery life in portable devices.
Once in shutdown mode the supply current is drastically
reduced, 1μA maximum, and the output will be "tri-stated."
The device will be disabled when the shutdown pin voltage is
pulled low. The shutdown pin should never be left uncon-
nected. Leaving the pin floating will result in an undefined
operation mode and the device may oscillate between shut-
down and active modes.
The LMV341 typically turns on 2.8μs after the shutdown
voltage is pulled high. The device turns off in less than 400ns
after shutdown voltage is pulled low.
Figure 3
and
Figure 4
show the turn-on and turn-off time of the LMV341, respec-
tively. In order to reduce the effect of the capacitance added
to the circuit by the scope probe, in the turn-off time circuit a
resistive load of 600
is added.
Figure 5
and
Figure 6
show
the test circuits used to obtain the two plots.
20030453
FIGURE 1. Simplified Schematic
20030444
FIGURE 2. Sample and Hold Circuit
L
www.national.com
13
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| LMV342MM | Single with Shutdown/Dual/Quad General Purpose, 2.7V, Rail-to-Rail Output, 125∑C, Operational Amplifiers |
| LMV342MMX | Single with Shutdown/Dual/Quad General Purpose, 2.7V, Rail-to-Rail Output, 125∑C, Operational Amplifiers |
| LMV344MA | Single with Shutdown/Dual/Quad General Purpose, 2.7V, Rail-to-Rail Output, 125∑C, Operational Amplifiers |
| LMV344MAX | Single with Shutdown/Dual/Quad General Purpose, 2.7V, Rail-to-Rail Output, 125∑C, Operational Amplifiers |
| LMV344MT | Single with Shutdown/Dual/Quad General Purpose, 2.7V, Rail-to-Rail Output, 125∑C, Operational Amplifiers |
相關代理商/技術參數 |
參數描述 |
|---|---|
| LMV342MAX/NOPB | 功能描述:運算放大器 - 運放 RoHS:否 制造商:STMicroelectronics 通道數量: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 轉換速度:0.89 V/us 關閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LMV342MAX/S7002483 | 制造商:Texas Instruments 功能描述: |
| LMV342MM | 功能描述:運算放大器 - 運放 RoHS:否 制造商:STMicroelectronics 通道數量: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 轉換速度:0.89 V/us 關閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LMV342MM | 制造商:Texas Instruments 功能描述:OP AMP QUAD RRO/P SMD MSOP8 342 |
| LMV342MM/NOPB | 功能描述:運算放大器 - 運放 RoHS:否 制造商:STMicroelectronics 通道數量: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 轉換速度:0.89 V/us 關閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
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