參數(shù)資料
型號: LMV422MMX
廠商: NATIONAL SEMICONDUCTOR CORP
元件分類: 運算放大器
英文描述: Dual Rail-to-Rail Output Operational Amplifier with
中文描述: DUAL OP-AMP, 5500 uV OFFSET-MAX, 8 MHz BAND WIDTH, PDSO10
封裝: 3 X 5 MM, MSOP-10
文件頁數(shù): 9/10頁
文件大?。?/td> 761K
代理商: LMV422MMX
Application Information
(Continued)
AC COUPLED CIRCUITS
The two power modes makes the LMV422 ideal for AC
coupled circuit where the circuit needs to be kept active to
maintain a quiescent charge on the coupling capacitors with
minimum power consumption.
Figure 4
shows a schematic of an inverting and non-inverting
AC coupled amplifiers using the LMV422 with the PS pins
controlled by I/O ports of a microcontroller.
The advantage of the low power active mode for AC coupled
amplifiers is the elimination of the time needed to re-
establish a quiescent operating point when the amplifier is
switched to a full power mode. When amplifiers without a low
power active mode are used in low power applications, there
are two ways to minimize power consumption. The first is
turning off the amplifiers by switching off power to the op
amps using a transistor switch. The second is using an
amplifier with a shut down pin. Both of these methods have
the problem of allowing the coupling capacitors, C1, C2, C3,
C4, and C5, to discharge the quiescent DC voltage stored on
them when placed in the shut down state. When the ampli-
fiers are turned on again, the quiescent DC voltages must
reestablish themselves. During this time, the amplifier’s out-
put is not usable because the output signal is a mixture of the
amplified input signal and the charging voltage on the cou-
pling capacitors. The settling time can range from a several
milliseconds to several seconds depending on the resistor
and capacitor values.
When the LMV422 is placed into the low power mode the
power consumption is minimal but the amplifier is active to
maintain the quiescent DC voltage on the coupling capaci-
tors and the transition back to the operational high power
mode is fast, within few hundred nanoseconds. The active
low power mode of the LMV422 separates the two critical
aspects of a low power AC amplifier design. The values of
the gain resistors, bias resistors, and coupling capacitors
can be chosen independently of the turn on and stabilization
time.
RESISTIVE LOAD
The LMV422 has a minimum current drive of 3 mA in full
power mode. The minimum resistive load should be 10 k
The current drive in the low power mode is 140 uA, the
minimum resistive load should be 100 k
.
20109825
Figure 3a
20109826
Figure 3b
FIGURE 3.
20109834
FIGURE 4.
L
www.national.com
9
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