5965848599337719229410893895247870037AN573_a| Application Note
a
AN-573 APPLICATION NOTE
OP07 Is Still Evolving
by Reza Moghimi
One Technology Way P.O. Box 9106 Norwood, MA 02062-9106 Tel: 781/329-4700 FAX: 781/326-8703 www.analog.com
INTRODUCTION The OP07 has been tinkered with over the years, and versions of it are still available in plastic packages. This application note highlights some of the major features that the OP17x7 brings into new designs. A number of applications using these features are presented. SINGLE-SUPPLY OPERATION One of the biggest problems with the part in today's environment is that the OP07 requires dual supplies. A new family of amplifiers from Analog Devices addresses this problem while still giving a close replica of the original specifications. The OP777 single, OP727 dual, and OP747 quad operational amplifiers allow supplies from 15 V down to 1.35 V with split rails, and from +30 V down to +2.7 V with single rail operation. The data sheet characterizes the parts with rails of +5 V and 15 V. The OP7x7 family's true single-supply capability enables designers to operate down to the negative supply or ground in both single- and dual-supply applications.
5V R4 26.7k V+ 3
Figure 1 shows that the gain of the instrumentation amplifier (made up of U3 and U4) is set for 100. The AD589 establishes 1.235 V while the U1 amplifier servos the bridge while maintaining the voltage across the parallel combination of 2.55 M and 6.19 k to generate a 200 uA current source. This current splits evenly and flows into both halves of the bridge, eventually through RTD, and establishes an output voltage based upon its value. As shown in Figure 2, the circuit floats up from the single-supply (12 V to 30 V) return. It consumes only 1.5 mA, leaving 2.5 mA available to the user for powering other signal conditioning circuitry.
VIN 0V TO 3V
R23 10k R21 182k
R24 100k R20 1.21M V+ 3 2 R26 100
T1 2 3 Q1 2N1711 VIN TRIM VOUT GND C2 220pF R28 100k 5
12V TO 30V
OP777
1 R25 220
TWIST PAIR R29 100 4 20 mA
6
R22 1k D2
V
R3 37.4k
V2 R7 100
GAIN = 100 (V2 V1)
2 1 HP5082-2800
REF-02A/D 4
R27 10k
AD589
N D1
2
U1 V
1
1/4 OP747
R2 200 RTD 100
Figure 2. Self-Powered 4 20 mA Current Loop Transmitter
V1 R12 1M R4 10.1k U4 U3 VOUT
R5 26.7k R8 2.55M R9 6.19k
1/4 OP747
R14 10.1k
1/4 OP747
R15 1M
Figure 1. Low Power Single-Supply RTD Amplifier
REV. A
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