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AD629_07

更新时间: 2024-10-28 04:04:11
品牌 Logo 应用领域
亚德诺 - ADI 放大器
页数 文件大小 规格书
16页 533K
描述
High Common-Mode Voltage, Difference Amplifier

AD629_07 数据手册

 浏览型号AD629_07的Datasheet PDF文件第7页浏览型号AD629_07的Datasheet PDF文件第8页浏览型号AD629_07的Datasheet PDF文件第9页浏览型号AD629_07的Datasheet PDF文件第11页浏览型号AD629_07的Datasheet PDF文件第12页浏览型号AD629_07的Datasheet PDF文件第13页 
AD629  
APPLICATIONS  
+V  
S
AD629  
REF (–)  
21.1k  
BASIC CONNECTIONS  
NC  
1
2
3
4
8
7
6
5
Figure 37 shows the basic connections for operating the AD629  
with a dual supply. A supply voltage of between ±3 ꢁ and ±18 ꢁ  
is applied between Pin ꢀ and Pin 4. Both supplies should be  
decoupled close to the pins using 7.1 μF capacitors. Electrolytic  
capacitors of 17 μF, also located close to the supply pins, may be  
required if low frequency noise is present on the power supply.  
While multiple amplifiers can be decoupled by a single set of  
17 μF capacitors, each in amp should have its own set of 7.1 μF  
capacitors so that the decoupling point can be located right at  
the ICs power pins.  
380k380kΩ  
–IN  
+IN  
V
+V  
0.1µF  
X
S
I
R
SHUNT  
SHUNT  
380kΩ  
V
Y
20kΩ  
–V  
S
REF (+)  
OUTPUT = V  
OUT  
– V  
REF  
NC = NO CONNECT  
V
REF  
Figure 31. Operation with a Single Supply  
+V  
S
Applying a reference voltage to REF(+) and REF(–) and  
+3V TO +18V  
NC  
AD629  
REF (–)  
21.1kΩ  
1
2
3
4
8
7
6
5
operating on a single supply reduces the input common-mode  
range of the AD629. The new input common-mode range  
depends upon the voltage at the inverting and noninverting  
inputs of the internal operational amplifier, labeled ꢁX and ꢁY  
in Figure 31. These nodes can swing to within 1 ꢁ of either rail.  
Therefore, for a (single) supply voltage of 17 , X and ꢁY can  
range between 1 ꢁ and 9 . If ꢁREF is set to ± , the permissible  
common-mode range is +8± ꢁ to –ꢀ± . The common-mode  
voltage ranges can be calculated by  
380k380kΩ  
–IN  
+IN  
(SEE  
TEXT)  
+V  
0.1µF  
S
I
R
SHUNT  
SHUNT  
380kΩ  
V
= I  
SHUNT  
× R  
SHUNT  
OUT  
20kΩ  
–V  
S
REF (+)  
(SEE  
TEXT)  
0.1µF  
NC = NO CONNECT  
–V  
S
–3V TO –18V  
Figure 30. Basic Connections  
V
CM (±) = 27 VX/VY(±) − 19 VREF  
The differential input signal, which typically results from a load  
current flowing through a small shunt resistor, is applied to  
Pin 2 and Pin 3 with the polarity shown to obtain a positive  
gain. The common-mode range on the differential input signal  
can range from −2ꢀ7 ꢁ to +2ꢀ7 , and the maximum differential  
range is ±13 . When configured as shown in Figure 37, the  
device operates as a simple gain-of-1, differential-to-single-  
ended amplifier; the output voltage being the shunt resistance  
times the shunt current. The output is measured with respect to  
Pin 1 and Pin ±.  
SYSTEM-LEVEL DECOUPLING AND GROUNDING  
The use of ground planes is recommended to minimize the  
impedance of ground returns (and therefore the size of dc  
errors). Figure 32 shows how to work with grounding in a  
mixed-signal environment, that is, with digital and analog  
signals present. To isolate low level analog signals from a noisy  
digital environment, many data acquisition components have  
separate analog and digital ground returns. All ground pins  
from mixed-signal components, such as ADCs, should return  
through a low impedance analog ground plane. Digital ground  
lines of mixed-signal converters should also be connected to the  
analog ground plane. Typically, analog and digital grounds  
should be separated; however, it is also a requirement to  
minimize the voltage difference between digital and analog  
grounds on a converter, to keep them as small as possible  
(typically <7.3 ꢁ). The increased noise, caused by the  
converter’s digital return currents flowing through the analog  
ground plane, is typically negligible. Maximum isolation  
between analog and digital is achieved by connecting the ground  
planes back at the supplies. Note that Figure 32 suggests a “star”  
ground system for the analog circuitry, with all ground lines  
being connected, in this case, to the ADCs analog ground.  
However, when ground planes are used, it is sufficient to  
connect ground pins to the nearest point on the low impedance  
ground plane.  
Pin 1 and Pin ± (REF(–) and REF(+)) should be grounded for a  
gain of unity and should be connected to the same low impedance  
ground plane. Failure to do this results in degraded common-  
mode rejection. Pin 8 is a no connect pin and should be left open.  
SINGLE-SUPPLY OPERATION  
Figure 31 shows the connections for operating the AD629 with  
a single supply. Because the output can swing to within only  
about 2 ꢁ of either rail, it is necessary to apply an offset to the  
output. This can be conveniently done by connecting REF(+)  
and REF(–) to a low impedance reference voltage (some ADCs  
provide this voltage as an output), which is capable of sinking  
current. Therefore, for a single supply of 17 , REF may be set  
to ± ꢁ for a bipolar input signal. This allows the output to swing  
±3 ꢁ around the central ± ꢁ reference voltage. Alternatively, for  
unipolar input signals, ꢁREF can be set to about 2 , allowing the  
output to swing from 2 ꢁ (for a 7 ꢁ input) to within 2 ꢁ of the  
positive rail.  
Rev. B | Page 1ꢀ of 16  
 
 
 

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