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XTR101AG 参数 Datasheet PDF下载

XTR101AG图片预览
型号: XTR101AG
PDF下载: 下载PDF文件 查看货源
内容描述: 高精度,低漂移的4-20mA两线制变送器 [Precision, Low Drift 4-20mA TWO-WIRE TRANSMITTER]
分类和应用:
文件页数/大小: 15 页 / 197 K
品牌: BB [ BURR-BROWN CORPORATION ]
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eIN  
RS  
+
(e1)  
(e2)  
IS  
5
6
I3  
I4  
R3  
R4  
1.25kΩ  
1.25kΩ  
+VCC  
A1  
+VCC  
A2  
+VCC  
8
D1  
(e1)  
IB1  
–In3  
eIN  
IB2  
VPS  
+In4  
(e2)  
100µA  
IO  
7
+
Q1  
+VCC  
eL  
+VCC  
A3  
RL  
2mA  
I1  
R
1kΩ  
1
R
2
52.6Ω  
I2  
IO  
Voltage Controlled  
Current Source  
10  
IREF1  
11  
IREF2  
2.5kΩ  
IO = 4mA + (0.016 + 40/RS) eIN, eIN = e2 – e1  
FIGURE 1. Simplified Schematic of the XTR101.  
and minimizes thermal feedback to the input stage. Also in  
such applications where eIN full scale is small (<50mV) and  
tions shown in Figure 2. Thus the 2N2222 will safely  
operate below its 400mW rating at the upper temperature  
of +85°C. Heat sinking the 2N2222 will result in greatly  
reduced accuracy improvement and is not recommended.  
RSPAN is small (<150), caution should be taken to consider  
errors from the external span circuit plus high amplification  
of offset drift and noise.  
2. TIP29B in the TO-220 package. This transistor will  
operate over the specified temperature and output voltage  
range without a series collector resistor. Heat sinking the  
TIP29B will result in slightly less accuracy improvement.  
It can be done, however, when mechanical constraints  
require it.  
OPTIONAL EXTERNAL TRANSISTOR  
The optional external transistor, when used, is connected in  
parallel with the XTR101’s internal transistor. The purpose  
is to increase accuracy by reducing heat change inside the  
XTR101 package as the output current spans from 4-20mA.  
Under normal operating conditions, the internal transistor is  
never completely turned off as shown in Figure 2. This  
maintains frequency stability with varying external transis-  
tor characteristics and wiring capacitance. The actual “cur-  
rent sharing” between internal and external transistors is  
dependent on two factors: (1) relative geometry of emitter  
areas and (2) relative package dissipation (case size and  
thermal conductivity). For best results, the external device  
should have a larger base-emitter area and smaller package.  
It will, upon turn on, take about [0.95 (IO – 3.3mA)]mA.  
However, it will heat faster and take a greater share after a  
few seconds.  
ACCURACY WITH AND  
WITHOUT EXTERNAL TRANSISTOR  
The XTR101 has been tested in a circuit using an external  
transistor. The relative difference in accuracy with and  
without an external transistor is shown in Figure 3. Notice  
that a dramatic improvement in offset voltage change with  
supply voltage is evident for any value of load resistor.  
MAJOR POINTS TO  
CONSIDER WHEN USING THE XTR101  
1. The leads to RS should be kept as short as possible to  
reduce noise pick-up and parasitic resistance.  
Although any NPN of suitable power rating will operate  
with the XTR101, two readily available transistors are  
recommended.  
2. +VCC should be bypassed with a 0.01µF capacitor as close  
to the unit as possible (pin 8 to 7).  
3. Always keep the input voltages within their range of  
linear operation, +4V to +6V (e1 and e2 measured with  
respect to pin 7).  
1. 2N2222 in the TO-18 package. For power supply volt-  
ages above 24V, a 750, 1/2W resistor should be con-  
nected in series with the collector. This will limit the  
power dissipation to 377mW under the worst-case condi-  
®
XTR101  
6