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AD822AR-3V 参数 Datasheet PDF下载

AD822AR-3V图片预览
型号: AD822AR-3V
PDF下载: 下载PDF文件 查看货源
内容描述: 单电源,轨到轨低功耗FET输入运算放大器 [Single Supply, Rail-to-Rail Low Power FET-Input Op Amp]
分类和应用: 运算放大器
文件页数/大小: 16 页 / 322 K
品牌: ADI [ ADI ]
 浏览型号AD822AR-3V的Datasheet PDF文件第8页浏览型号AD822AR-3V的Datasheet PDF文件第9页浏览型号AD822AR-3V的Datasheet PDF文件第10页浏览型号AD822AR-3V的Datasheet PDF文件第11页浏览型号AD822AR-3V的Datasheet PDF文件第12页浏览型号AD822AR-3V的Datasheet PDF文件第13页浏览型号AD822AR-3V的Datasheet PDF文件第15页浏览型号AD822AR-3V的Datasheet PDF文件第16页  
AD822  
T he AD822 is designed for 13 nV/Hz wideband input voltage  
noise and maintains low noise performance to low frequencies  
(refer to Figure 11). T his noise performance, along with the  
AD822s low input current and current noise means that the  
AD822 contributes negligible noise for applications with source  
resistances greater than 10 kand signal bandwidths greater  
than 1 kHz. T his is illustrated in Figure 40.  
20mV  
2µ s  
100  
90  
10  
100k  
0%  
WHENEVER JOHNSON NOISE IS GREATER THAN  
AMPLIFIER NOISE, AMPLIFIER NOISE CAN BE  
CONSIDERED NEGLIGIBLE FOR APPLICATION.  
10k  
1k  
1kHz  
Figure 41. Sm all Signal Response of AD822 as Unity Gain  
Follower Driving 350 pF Capacitive Load  
RESISTOR JOHNSON  
NOISE  
100  
10  
5
10Hz  
4
3
1
AMPLIFIER GENERATED  
NOISE  
0.1  
10k  
100k  
1M  
10M  
100M  
1G  
10G  
SOURCE IMPEDANCE – Ω  
Figure 40. Total Noise vs. Source Im pedance  
2
1
O UTP UT CH ARACTERISTICS  
T he AD822 s unique bipolar rail-to-rail output stage swings  
within 5 mV of the minus supply and 10 mV of the positive  
supply with no external resistive load. T he AD822s  
approximate output saturation resistance is 40 sourcing and  
20 sinking. T his can be used to estimate output saturation  
voltage when driving heavier current loads. For instance, when  
sourcing 5 mA, the saturation voltage to the positive supply rail  
will be 200 mV, when sinking 5 mA, the saturation voltage to  
the minus rail will be 100 mV.  
300  
1k  
3k  
10k  
30k  
CAPACITIVE LOAD FOR 20  
°
PHASE MARGIN – pF  
R
F
C
L
R
I
T he amplifier’s open-loop gain characteristic will change as a  
function of resistive load, as shown in Figures 7 through 10. For  
load resistances over 20 k, the AD822s input error voltage is  
virtually unchanged until the output voltage is driven to 180 mV  
of either supply.  
Figure 42. Capacitive Load Tolerance vs. Noise Gain  
Figure 43 shows a method for extending capacitance load drive  
capability for a unity gain follower. With these component  
values, the circuit will drive 5,000 pF with a 10% overshoot.  
If the AD822s output is overdriven so as to saturate either of  
the output devices, the amplifier will recover within 2 µs of its  
input returning to the amplifier’s linear operating region.  
+V  
S
0.01µF  
8
100Ω  
Direct capacitive loads will interact with the amplifier’s effective  
output impedance to form an additional pole in the amplifier’s  
feedback loop, which can cause excessive peaking on the pulse  
response or loss of stability. Worst case is when the amplifier is  
used as a unity gain follower. Figure 41 shows the AD822s  
pulse response as a unity gain follower driving 350 pF. T his  
amount of overshoot indicates approximately 20 degrees of  
phase margin—the system is stable, but is nearing the edge.  
Configurations with less loop gain, and as a result less loop  
bandwidth, will be much less sensitive to capacitance load  
effects. Figure 42 is a plot of capacitive load that will result in a  
20 degree phase margin versus noise gain for the AD822. Noise  
gain is the inverse of the feedback attenuation factor provided  
by the feedback network in use.  
1/2  
V
IN  
AD822  
V
0.01µF  
OUT  
4
C
L
–V  
S
20pF  
20kΩ  
Figure 43. Extending Unity Gain Follower Capacitive Load  
Capability Beyond 350 pF  
REV. A  
–14–