參數(shù)資料
型號: LMV951MKX
廠商: NATIONAL SEMICONDUCTOR CORP
元件分類: 運動控制電子
英文描述: 1V, 2.7 MHz, Rail-to-Rail Input and Output Amplifier with Shutdown Option
中文描述: OP-AMP, 3000 uV OFFSET-MAX, 2.7 MHz BAND WIDTH, PDSO6
封裝: SOT-23, 6 PIN
文件頁數(shù): 15/17頁
文件大?。?/td> 1147K
代理商: LMV951MKX
Application Information
(Continued)
BRIDGE CONFIGURATION AMPLIFIER
Some applications may benefit from doubling the voltage
across the load. With V
+
= 1V a bridge configuration can
provide a 2 V
output to the load with a resistance as low as
300
. The output stage of the LMV951 enables it to drive a
load of 120
and still swing at least 70% of the supply rails.
The bridge configuration shown in
Figure 4
enables the
amplifier to maintain a low dropout voltage thus maximizing
its dynamic range. It has been configured in a gain of 1 and
uses the fewest number of parts.
Resistor values have been selected to keep the current
consumption to a minimum and voltage errors due to bias
currents negligible. Using the selected resistor values makes
this circuit quite practical in a battery operated design. R
, R
2
and R
, R
set up a virtual ground that is half of V
+
. Note that
the accuracy of the resistor values will establish how well the
two virtual grounds match. Any errors in the virtual grounds
will show as current across R
L
when there is no input signal.
AC coupling the input signal sets the DC bias point of this
signal to the virtual ground of the circuit. Using the large
resistor values with a 1 μF capacitor (C
1
) sets the frequency
rolloff of this circuit below 10 Hz.
C
2
and C
3
are .01 μF ceramic capacitors that must be
located as close as possible to pin 6, the V
+
pin. As
covered in the power supply bypassing section these
capacitors must have low ESR and a self resonant fre-
quency above 15 MHz.
C
4
is a 1 μF tantalum or electrolytic capacitor that should
also be located close to the supply pin.
To use the shutdown feature tie pin 5 of the two parts
together and connect through a 470 k
resistor to V
+
.
Add a switch between pin 5 and ground. Closing the
switch keeps the parts in the active mode, opening the
switch sets the parts in the shutdown mode without add-
ing any additional current to V
+
.
VIRTUAL GROUND CIRCUIT
The front page of this data sheet shows the LMV951 being
used in a system establishing a virtual ground. Having a
buffered output stage gives this part the ability to handle load
currents higher than 35 mA at 1V.
R
3
and R
4
are used to set the voltage of the virtual ground.
To maintain low noise the values should be between 1 k
and 10 k
. C
1
and C
2
provide the recommended bypassing
for the LMV951. These caps must be placed as close as
possible to pins 2 and 6.
TWO WIRE LINE TRANSMISSION
The robust output stage of the LMV951 makes it an excellent
choice for driving long cables. The circuit shown below in
Figure 5
can drive a long cable using only two wires; power
and ground.
When many sensors are located remotely from the control
area the wiring becomes a significant expense. Using only
two wires helps minimize the wiring expense in a large
project such as an industrial plant.
Figure 6
shows a 25 kHz
signal after passing though 1000 ft. of twisted pair cable.
Figure 7
shows a 200 kHz signal after passing through 50 ft.
of twisted pair cable.
20123144
FIGURE 4. Bridge Amplifier
L
www.national.com
15
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