Circuit Note CN-0289 Devices Connected/Referenced Wide Supply Range, Rail-to-Rail AD8226 Circuits from the Lab reference circuits are engineered and Output Instrumentation Amplifier tested for quick and easy system integration to help solve todays Ultracompact, Precision 5.0 V Voltage analog, mixed-signal, and RF design challenges. For more ADR02 Reference information and/or support, visit www.analog.com/CN0289. Precision Micropower, OVP, RRIO ADA4091-2 Dual Op Amp Flexible, 4 mA-to-20 mA, Loop-Powered Pressure Sensor Transmitter with Voltage or Current Drive The design is optimized for a wide variety of bridge based voltage EVALUATION AND DESIGN SUPPORT or current driven pressure sensors, utilizes only four active Circuit Evaluation Boards devices, and has a total unadjusted error of less than 1%. The CN0289 Evaluation Board (EVAL-CN0289-EB1Z) loop supply voltage can range from 12 V to 36 V. Design and Integration Files Schematics, Layout Files, Bill of Materials The input of the circuit is protected for ESD and voltages beyond the supply rail, making it ideal for industrial CIRCUIT FUNCTION AND BENEFITS applications. The circuit shown in Figure 1 is a robust and flexible loop- powered current transmitter that converts the differential voltage output from a pressure sensor to a 4 mA-to-20 mA current output. +5V +V LOOP I I CIRCUIT LOOP J2-1 V V +5V OUT IN U3 U2A ADR02 1/2 ADA4091-2 39.60A V LOOP SUPPLY V I R12 +V DRIVE G = 50.00 12 LOOP I I 126.25k LOOP CIRCUIT +V LOOP J1-3 +V LOOP 1nF R R V BRIDGE BRIDGE OUT U2B R1 12V 0V, 5.00V Q1 J1-2 1/2 4.02k TO ZXT13N50DE6TA ADA4091-2 R5 R9 36V 10k 30k 10nF 31.56k U1 R R R3 BRIDGE BRIDGE AD8226 R2 1.008k J1-4 4.02k R6 I 9 I REF CIRCUIT 10k J2-2 0A, 1nF J1-1 158.42A LOOP 3.960mA, LOAD 19.802mA 0V R10 PCB GROUND R8 R7 I I 10 8 V : 1k 0mV, 100mV 39.60mV, 198.02mV 10 250 IN + 39.60A, 198.02A I I 10 LOOP I : 4.000mA, 20.000mA LOOP LOOP GROUND NOTES 1. R8, R10 ARE STANDARD 0.1% VALUES. R5, R6 ARE STANDARD 1% VALUES. R3, R9, R12 ARE CALCULATED VALUES (SEE TEXT). 2. VOLTAGES MEASURED WITH RESPECT TO PCB GROUND. Figure 1. Robust Loop Powered Pressure Sensor Signal Conditioning Circuit with 4 mA-to-20 mA Output (Shown in Sensor Voltage Drive Mode) Simplified Schematic: All Connections and Decoupling Not Shown Rev. 0 Circuits from the Lab circuits from Analog Devices have been designed and built by Analog Devices engineers. Standard engineering practices have been employed in the design and construction of each circuit, and their function and performance have been tested and verified in a lab environment at room temperature. However, you are solely responsible for testing the circuit and determining its One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. suitability and applicability for your use and application. Accordingly, in no event shall Analog Devices Tel: 781.329.4700 www.analog.com be liable for direct, indirect, special, incidental, consequential or punitive damages due to any cause Fax: 781.461.3113 2013 Analog Devices, Inc. All rights reserved. whatsoever connected to the use of any Circuits from the Lab circuits. (Continued on last page) 10947-001CN-0289 Circuit Note CIRCUIT DESCRIPTION Sensor Excitation Drive The design provides a complete solution for the 4 mA-to-20 mA Depending on the pressure sensor selected, either a voltage or transmitter for pressure sensor measurements where the supply current drive is required. The circuit uses one half of the for the entire circuit is provided by the loop. The circuit has ADA4091-2 (U2A) with different configurations chosen by three critical stages: the sensor excitation drive, sensor output switching S1 to support either option. The switch S1 provides amplifier, and the voltage to current converter. the selection for either drive. The total current required by the circuit is 1.82 mA (maximum) Excitation: Voltage Drive Configuration as shown in Table 1. Pressure sensors requiring bridge drive Figure 2 shows the configuration for the voltage drive with S1 in currents of up to 2 mA can therefore be used without exceeding the position labeled VOLTAGE DRIVE on the PCB (see the maximum available loop current of 4 mA. complete circuit layout and schematics in the CN0289 design support package: