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OPA2348AIDR 参数 Datasheet PDF下载

OPA2348AIDR图片预览
型号: OPA2348AIDR
PDF下载: 下载PDF文件 查看货源
内容描述: 为1MHz , 45レA, CMOS ,轨至轨运算放大器 [1MHz, 45レA, CMOS, Rail-to-Rail OPERATIONAL AMPLIFIERS]
分类和应用: 运算放大器
文件页数/大小: 19 页 / 502 K
品牌: BB [ BURR-BROWN CORPORATION ]
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Normally, input currents are 0.5pA. However, large inputs  
(greater than 500mV beyond the supply rails) can cause  
excessive current to flow in or out of the input pins. There-  
fore, as well as keeping the input voltage below the maxi-  
mum rating, it is also important to limit the input current to  
less than 10mA. This is easily accomplished with an input  
voltage resistor, as shown in Figure 4.  
In unity-gain inverter configuration, phase margin can be  
reduced by the reaction between the capacitance at the op  
amp input, and the gain setting resistors, thus degrading  
capacitive load drive. Best performance is achieved by using  
small valued resistors. For example, when driving a 500pF  
load, reducing the resistor values from 100kto 5kde-  
creases overshoot from 55% to 13% (see the typical charac-  
teristic Small-Signal Overshoot vs. Load Capacitance).  
However, when large valued resistors cannot be avoided, a  
small (4pF to 6pF) capacitor, CFB, can be inserted in the  
feedback, as shown in Figure 6. This significantly reduces  
overshoot by compensating the effect of capacitance, CIN,  
which includes the amplifier's input capacitance and PC  
board parasitic capacitance.  
+5V  
IOVERLOAD  
10mA max  
VOUT  
OPA348  
VIN  
5kΩ  
FIGURE 4. Input Current Protection for Voltages Exceeding  
the Supply Voltage.  
CFB  
RF  
RAIL-TO-RAIL OUTPUT  
A class AB output stage with common-source transistors is  
used to achieve rail-to-rail output. This output stage is ca-  
pable of driving 5kloads connected to any potential be-  
tween V+ and ground. For light resistive loads (> 100k), the  
output voltage can typically swing to within 18mV from supply  
rail. With moderate resistive loads (10kto 50k), the output  
voltage can typically swing to within 100mV of the supply  
rails while maintaining high open-loop gain (see the typical  
characteristic Output Voltage Swing vs Output Current).  
RI  
VIN  
VOUT  
OPA348  
CIN  
CL  
FIGURE 6. Improving Capacitive Load Drive.  
CAPACITIVE LOAD AND STABILITY  
DRIVING A/D CONVERTERS  
The OPA348 in a unity-gain configuration can directly drive  
up to 250pF pure capacitive load. Increasing the gain en-  
hances the amplifiers ability to drive greater capacitive loads  
(see the typical characteristic Small-Signal Overshoot vs  
Capacitive Load). In unity-gain configurations, capacitive  
load drive can be improved by inserting a small (10to 20)  
resistor, RS, in series with the output, as shown in Figure 5.  
This significantly reduces ringing while maintaining DC per-  
formance for purely capacitive loads. However, if there is a  
resistive load in parallel with the capacitive load, a voltage  
divider is created, introducing a Direct Current (DC) error at  
the output and slightly reducing the output swing. The error  
introduced is proportional to the ratio RS/RL, and is generally  
negligible.  
The OPA348 series op amps are optimized for driving  
medium-speed sampling Analog-to-Digital Converters (ADCs).  
The OPA348 op amps buffer the ADCs input capacitance  
and resulting charge injection while providing signal gain.  
The OPA348 in a basic noninverting configuration driving the  
ADS7822, see Figure 7. The ADS7822 is a 12-bit,  
microPOWER sampling converter in the MSOP-8 package.  
When used with the low-power, miniature packages of the  
OPA348, the combination is ideal for space-limited, low-  
power applications. In this configuration, an RC network at  
the ADCs input can be used to provide for anti-aliasing filter  
and charge injection current.  
The OPA348 in noninverting configuration driving ADS7822  
limited, low-power applications. In this configuration, an RC  
network at the ADCs input can be used to provide for anti-  
aliasing filter and charge injection current. See Figure 8 for  
the OPA2348 driving an ADS7822 in a speech bandpass  
filtered data acquisition system. This small, low-cost solution  
provides the necessary amplification and signal conditioning  
to interface directly with an electret microphone. This circuit  
will operate with VS = 2.7V to 5V with less than 250µA typical  
quiescent current.  
V+  
RS  
VOUT  
OPA348  
10to  
20Ω  
VIN  
CL  
RL  
FIGURE 5. Series Resistor in Unity-Gain Buffer Configura-  
tion Improves Capacitive Load Drive.  
OPA348, 2348, 4348  
8
SBOS213C  
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