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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10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页浏览型号AD629_07的Datasheet PDF文件第14页 
AD629  
ANALOG POWER  
SUPPLY  
DIGITAL  
POWER SUPPLY  
GND +5V  
Table 3 shows some sample error voltages generated by a  
common-mode voltage of 277 ꢁ dc with shunt resistors from  
27 Ω to 2777 Ω. Assuming that the shunt resistor is selected to  
use the full ±17 ꢁ output swing of the AD629, the error voltage  
becomes quite significant as RSHUNT increases.  
–5V  
+5V  
GND  
0.1µF  
0.1µF  
0.1µF 0.1µF  
1
6
14  
AGND DGND  
Table 3. Error Resulting from Large Values of RSHUNT  
(Uncompensated Circuit)  
4
7
V
DD  
V
DD  
GND  
12  
–V  
+V  
S
S
3
2
+IN  
–IN  
MICROPROCESSOR  
V
V
6
4
3
OUTPUT  
AD629  
IN1 AD7892-2  
RS (Ω)  
2ꢀ  
Error VOUT (V)  
Error Indicated (mA)  
REF(–) REF(+)  
IN2  
ꢀ.ꢀ1  
ꢀ.498  
1
ꢀ.5  
1
5
1ꢀꢀꢀ  
2ꢀꢀꢀ  
ꢀ.498  
ꢀ.5  
Figure 32. Optimal Grounding Practice for a Bipolar Supply Environment  
with Separate Analog and Digital Supplies  
POWER SUPPLY  
To measure low current or current near zero in a high common-  
mode environment, an external resistor equal to the shunt  
resistor value can be added to the low impedance side of the  
shunt resistor, as shown in Figure 34.  
+5V  
GND  
0.1µF  
0.1µF  
0.1µF  
+V  
S
7
4
AD629  
REF (–)  
V
AGND DGND  
21.1k  
DD  
+V  
–V  
S
NC  
1
2
3
4
8
7
6
5
S
V
GND  
DD  
3
2
+IN  
–IN  
V
V
6
OUTPUT  
IN1  
AD629  
MICROPROCESSOR  
R
R
380k380kΩ  
COMP  
–IN  
+IN  
ADC  
IN2  
REF(–) REF(+)  
0.1µF  
+V  
S
I
1
5
SHUNT  
SHUNT  
380kΩ  
V
OUT  
Figure 33. Optimal Ground Practice in a Single-Supply Environment  
20kΩ  
–V  
REF (+)  
S
If there is only a single power supply available, it must be shared  
by both digital and analog circuitry. Figure 33 shows how to  
minimize interference between the digital and analog circuitry.  
In this example, the ADCs reference is used to drive Pin REF(+)  
and Pin REF(–). This means that the reference must be capable  
of sourcing and sinking a current equal to ꢁCM/277 kΩ. As in  
the previous case, separate analog and digital ground planes  
should be used (reasonably thick traces can be used as an  
alternative to a digital ground plane). These ground planes  
should connect at the power supplys ground pin. Separate  
traces (or power planes) should run from the power supply to  
the supply pins of the digital and analog circuits. Ideally, each  
device should have its own power supply trace, but these can be  
shared by a number of devices, as long as a single trace is not  
used to route current to both digital and analog circuitry.  
0.1µF  
–V  
S
NC = NO CONNECT  
Figure 34. Compensating for Large Sense Resistors  
OUTPUT FILTERING  
A simple 2-pole, low-pass Butterworth filter can be implemented  
using the OP1ꢀꢀ after the AD629 to limit noise at the output, as  
shown in Figure 3±. Table 4 gives recommended component  
values for various corner frequencies, along with the peak-to-  
peak output noise for each case.  
+V  
S
AD629  
REF (–)  
21.1k  
NC  
1
2
3
4
8
7
6
5
+V  
S
C1  
0.1µF  
R1  
0.1µF  
0.1µF  
380k380kΩ  
–IN  
+IN  
+V  
S
V
OP177  
OUT  
R2  
C2  
380kΩ  
USING A LARGE SENSE RESISTOR  
20kΩ  
REF (+)  
–V  
S
Insertion of a large value shunt resistance across the input pins,  
Pin 2 and Pin 3, will imbalance the input resistor network,  
introducing a common-mode error. The magnitude of the error  
will depend on the common-mode voltage and the magnitude  
–V  
S
0.1µF  
NC = NO CONNECT  
Figure 35. Filtering of Output Noise Using a 2-Pole Butterworth Filter  
of RSHUNT  
.
Table 4. Recommended Values for 2-Pole Butterworth Filter  
Corner Frequency  
R1  
R2  
C1  
C2  
Output Noise (p-p)  
No Filter  
5ꢀ kHz  
5 kHz  
5ꢀꢀ Hz  
5ꢀ Hz  
3.2 mV  
1 mV  
ꢀ.32 mV  
1ꢀꢀ μV  
32 μV  
2.94 kΩ 1%  
2.94 kΩ 1%  
2.94 kΩ 1%  
2.7 kΩ 1ꢀ%  
1.58 kΩ 1%  
1.58 kΩ 1%  
1.58 kΩ 1%  
1.5 kΩ 1ꢀ%  
2.2 nF 1ꢀ%  
22 nF 1ꢀ%  
22ꢀ nF 1ꢀ%  
2.2 μF 2ꢀ%  
1 nF 1ꢀ%  
1ꢀ nF 1ꢀ%  
ꢀ.1 μF 1ꢀ%  
1 μF 2ꢀ%  
Rev. B | Page 11 of 16  
 
 
 
 
 
 
 

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