APPLICATION BULLETIN ® Mailing Address: PO Box 11400 • Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd. • Tucson, AZ 85706 Tel: (602) 746-1111 • Twx: 910-952-111 • Telex: 066-6491 • FAX (602) 889-1510 • Immediate Product Info: (800) 548-6132 SINGLE SUPPLY 4-20mA CURRENT LOOP RECEIVER By R. Mark Stitt and David Kunst (602) 746-7445 inverted output signal, the RCV420 output will be 0 to –5V referenced to the pseudo ground. Since the pseudo ground is at 10V, the actual output will be 10V to 5V—a signal which can drive most floating ground meters. Many industrial current-loop data acquisition systems operate on a 24V or 28V single supply. You can make a singlesupply current loop receiver with the RCV420 by using its 10V reference as a pseudo ground. The RCV420 will convert a 4-20mA loop current into a 0 to 5V output voltage with no external components required. The current loop can be sourcing or sinking and can be referenced to either the power-supply V+ or ground. For a current loop receiver with a 4-20mA current sink referenced to the power-supply V+, use the connection shown in Figure 2. The circuit can operate on a single supply ranging from +15V to +36V (+44V absolute max). The pseudo ground (Ref Out) can source or sink up to 5mA. The complete circuit for a single-supply current loop receiver is shown in Figure 1. In this application, a 4-20mA current source referenced to power-supply ground drives the receiver. The V– terminal and the Ref Com terminal of the RCV420 are both tied to power supply ground. The 10V reference output (Ref Out) becomes a pseudo ground where the current loop receiver common pin (Rcv Com) is tied. The current loop receiver output is now referenced to the 10V pseudo ground. For an isolated single-supply 4-20mA current loop receiver, you can connect the circuit to an isolation amplifier as shown in Figure 3. In this circuit the ISO122 is operated single-supply using the 10.0V pseudo ground. Note that the output side of the isolation amplifier still requires dual supplies. Output from the ISO122 will be 0 to –5V. You could interchange the input connections to the ISO122 to get a 0 to 5V output, but power-supply rejection would degrade performance. In normal operation, the 4-20mA current loop signal would produce a 0-5V output with the RCV420 offset pin (Ref In) connected to the +10V reference. The 10V reference provides a –1.25V offset so 4mA input current will produce 0V out. In this application, the Ref In pin is connected to power supply ground which acts as a –10V reference—producing a +1.25V offset. Now with the inputs connected for an 4-20mA Input from Current Loop The ISO122 is a low-cost iso amp in a standard plastic DIP. For a hermetic isolation amplifier, use the ISO120. Hook-up details are shown in Application Bulletin AB-009. +28V (15V to 36V) V+ 16 300kΩ 1 RCV420 Ref 92kΩ In 12 Rcv 11.5kΩ FB 15 Ref Out 14 99kΩ –In 75Ω 2 CT NC (1) 3 Ref FB 10 1.01kΩ 75Ω 300kΩ 100kΩ 10.0V Ref +In V– 4 Rcv 13 Com Ref Out 11 10.0V to 5.0V LO 0 to 5V Meter HI 10.0V Pseudo Ground Ref 5 Com NOTE: (1) NC = No Connection. FIGURE 1. © 1992 Burr-Brown Corporation AB-041 Printed in U.S.A. June, 1992 +28V (15V to 36V) V+ 16 NC (1) RCV420 Ref 92kΩ In 12 Rcv 11.5kΩ FB 15 Ref Out 14 99kΩ 300kΩ 1 –In 75Ω 2 CT 100kΩ 300kΩ 3 10.0V Ref +In V– 4 LO 0 to 5V Meter Ref FB 10 1.01kΩ 75Ω 10.0V to 5.0V Rcv 13 Com HI 10.0V Pseudo Ground Ref Out 11 Ref 5 Com 4-20mA Input from Current Loop NOTE: (1) NC = No Connection. FIGURE 2. 4-20mA Input from Current Loop +28V (15V to 36V) V+ 16 300kΩ 1 RCV420 Ref 92kΩ In 12 Rcv 11.5kΩ FB 15 Ref Out 14 99kΩ –In 75Ω 2 CT 75Ω (1) NC 3 Ref FB 10 1.01kΩ 300kΩ 100kΩ 10.0V Ref +In V– 4 Rcv 13 Com 15 In 1 +VS2 (+15V) 9 ISO 122 7 8 10 16 Gnd 2 –VS1 VO = 0 to –5V Com 2 –VS2 (–15V) Ref Out 11 Ref 5 Com NOTE: (1) NC = No Connection. FIGURE 3. The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes no responsibility for the use of this information, and all use of such information shall be entirely at the user’s own risk. Prices and specifications are subject to change without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant any BURR-BROWN product for use in life support devices and/or systems. 2