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AD627ARZ 参数 Datasheet PDF下载

AD627ARZ图片预览
型号: AD627ARZ
PDF下载: 下载PDF文件 查看货源
内容描述: 微功耗,单电源和双电源,轨到轨仪表放大器 [Micropower, Single- and Dual-Supply, Rail-to-Rail Instrumentation Amplifier]
分类和应用: 仪表放大器
文件页数/大小: 24 页 / 1075 K
品牌: ADI [ ADI ]
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AD627  
The voltage on A± can also be expressed as a function of the  
actual voltages on the –IN and +IN pins (V− and V+ꢀ such that  
Table 6. Recommended Values of Gain Resistors  
VA1 = ±.25 ((V−ꢀ + 0.5 V) − 0.25 VREF − ((V+ꢀ − (V−ꢀꢀ 25 kΩ/RG (4ꢀ  
1% Standard Table  
Desired Gain  
Value of RG  
Resulting Gain  
5.00  
6.00  
7.00  
7.94  
The output of A± is capable of swinging to within 50 mV of the  
negative rail and to within 200 mV of the positive rail. It is clear,  
from either Equation 3 or Equation 4, that an increasing VREF  
(while it acts as a positive offset at the output of the AD627ꢀ  
tends to decrease the voltage on A±. Figure 31 and Figure 39  
show the maximum voltages that can be applied to the REF pin  
for a gain of 5 for both the single-supply and dual-supply cases.  
5
5
6
7
8
200 kΩ  
100 kΩ  
68.1 kΩ  
51.1 kΩ  
40.2 kΩ  
20 kΩ  
9
8.91  
9.98  
10  
15  
20  
25  
30  
40  
50  
60  
70  
80  
90  
100  
200  
500  
1000  
15.00  
19.60  
25.00  
29.81  
39.72  
49.15  
59.79  
69.72  
79.91  
89.39  
100.24  
195.48  
490.44  
980.61  
13.7 kΩ  
10 kΩ  
4
3
2
8.06 kΩ  
5.76 kΩ  
4.53 kΩ  
3.65 kΩ  
3.09 kΩ  
2.67 kΩ  
2.37 kΩ  
2.1 kΩ  
MAXIMUM V  
REF  
1
0
–1  
–2  
–3  
–4  
–5  
MINIMUM V  
REF  
1.05 kΩ  
412 Ω  
205 Ω  
0
1
2
3
4
–6  
–5  
–4  
–3  
–2  
–1  
V
(–) (V)  
IN  
Figure 38. Reference Input ꢀoltage vs. Negative Input ꢀoltage,  
S = ± ± ꢀ, G = +±  
REFERENCE TERMINAL  
5
The reference terminal potential defines the zero output voltage  
and is especially useful when the load does not share a precise  
ground with the rest of the system. It provides a direct means of  
injecting a precise offset to the output. The reference terminal is  
also useful when amplifying bipolar signals, because it provides  
a virtual ground voltage.  
MAXIMUM V  
REF  
4
3
2
1
The AD627 output voltage is developed with respect to the poten-  
tial on the reference terminal; therefore, tying the REF pin to the  
appropriate local ground solves many grounding problems. For  
optimal CMR, tie the REF pin to a low impedance point.  
MINIMUM V  
REF  
INPUT RANGE LIMITATIONS IN SINGLE-SUPPLY  
APPLICATIONS  
0
–0.5  
3.0  
3.5  
4.0  
4.5  
0
0.5  
1.0  
1.5  
2.0  
2.5  
V
(–) (V)  
IN  
In general, the maximum achievable gain is determined by the  
available output signal range. However, in single-supply applica-  
tions where the input common-mode voltage is nearly or equal  
to 0, some limitations on the gain can be set. Although the  
Specifications section nominally defines the input, output, and  
reference pin ranges, the voltage ranges on these pins are  
mutually interdependent. Figure 37 shows the simplified  
schematic of the AD627, driven by a differential voltage (VDIFFꢀ  
that has a common-mode component, VCM. The voltage on the  
A± op amp output is a function of VDIFF, VCM, the voltage on the  
REF pin, and the programmed gain. This voltage is given by  
Figure 39. Reference Input ꢀoltage vs. Negative Input ꢀoltage,  
S = ± ꢀ, G = +±  
Raising the input common-mode voltage increases the voltage  
on the output of A±. However, in single-supply applications  
where the common-mode voltage is low, a differential input  
voltage or a voltage on REF that is too high can drive the output  
of A± into the ground rail. Some low-side headroom is added  
because both inputs are shifted upwards by about 0.5 V (that is,  
by the VBE of Q± and Q2ꢀ. Use Equation 3 and Equation 4 to  
check whether the voltage on Amplifier A± is within its  
operating range.  
V
A1 = ±.25 (VCM + 0.5 Vꢀ − 0.25 VREF VDIFF (25 kΩ/RG − 0.625ꢀ (3ꢀ  
Rev. D | Page 16 of 24