Circuit Note CN-0325 Devices Connected/Referenced 16-Bit, Sigma-Delta 50 mA, High Voltage AD7795 ADP1720 ADC, 40 nV Noise Linear Regulator Circuits from the Lab reference designs 36 V Instrumentation Ultralow Noise, LDO are engineered and tested for quick AD8226 Amplifier, >90 dB ADR441 XFET, 2.5 V Voltage and easy system integration to help CMRR Reference solve todays analog, mixed-signal, 0.5C Digital Triple-Channel and RF design challenges. For more ADT7310 ADuM1311 Temperature Sensor Digital Isolator information and/or support, visit www.analog.com/CN0325. 36 V, 1 A, Step-Down, Quad Isolator ADP2441 DC-to-DC Regulator with Integrated ADuM3471 2 Transformer Driver LC MOS Quad SPST ADG442 and PWM Switch PLC and DCS Universal Analog Input Using Either 4-Pin or 6-Pin Terminal Block For the 4-terminal block channel (CH2), the voltage, current, EVALUATION AND DESIGN SUPPORT thermocouple, and RTD inputs all share the same 4 terminals, Circuit Evaluation Boards thus minimizing the number of terminal pins required. For the CN-0325 Evaluation Board (EVAL-CN0325-SDPZ) 6-pin terminal block channel (CH1), the voltage and current System Demonstration Platform (EVAL-SDP-CB1Z) inputs share a set of 3 terminals, and the thermocouple and RTD Design and Integration Files inputs share another set of 3 terminals this configuration requires Schematics, Layout Files, Bill of Materials more terminals but has a lower part count and component cost. CIRCUIT FUNCTION AND BENEFITS Figure 2 shows a photo of the printed circuit board (PCB), and Figure 3 shows a more detailed schematic of the circuit. The circuit shown in Figure 1 provides two, 16-bit, fully isolated, universal analog input channels suitable for programmable logic controllers (PLCs) and distributed control system (DCS) modules. Both channels are software programmable and support a number of voltage, current ranges, thermocouple, and RTD types, as shown in Figure 1. CURRENT: 0mA TO 20mA, 4mA TO 20mA, 20mA CH1: 6-PIN VOLTAGE: 0V TO 5V, 0V TO 10V, 5V, 10V TERMINAL THERMOCOUPLE: TYPE K, J, T, S BLOCK RTD: PT100, PT1000 SDP-B PC BOARD CURRENT: 0mA TO 20mA, 4mA TO 20mA, 20mA CH2: 4-PIN VOLTAGE: 0V TO 5V, 0V TO 10V, 5V, 10V TERMINAL THERMOCOUPLE: Type K, J, T, S BLOCK RTD: PT100, PT1000 Figure 1. Universal Analog Input Overview The evaluation board contains two different fully isolated universal input channels, one with a 4-pin terminal block (CH2), and one with a 6-pin terminal block (CH1). Figure 2. Universal Analog Input Board Rev. 0 Circuits from the Lab reference designs 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 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. determining its suitability and applicability for your use and application. Accordingly, in no event shall Tel: 781.329.4700 www.analog.com Analog Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due to any cause whatsoever connected to the use of any Circuits from the Lab circuits. (Continued on last page) Fax: 781.461.3113 2015 Analog Devices, Inc. All rights reserved. 11462-001 11462-002CN-0325 Circuit Note CH2: 4-PIN TERMINAL BLOCK FOR COMPACT SOLUTION AVDD DVDD 5V (AVDD/DVDD) 0.1F 0.1F +15V 15V R5 ADP1720 AVDD DVDD D1 2. 2k ADR441 IOUT1 AD7795 15V +15V R2 AD8226 ADG442 R9 2. 2k REFIN2(+) V1+ S1 V 10k INA1 AIN1+ S2 R3 R10 REFIN2() 2. 2k V1 S3 2k R6 R7 AIN1 24V R1 1M 1M S4 2.5V 249 I1 AIN2+ 5V IN1 IN2 IN3 IN4 ADuM3471 ADP2441 AIN2 Vm R8 P1 D2 2. 2k IOUT2 CS R4 CLK 2. 2k REFIN1(+) DIN R11 DOUT 4. 75k REFIN1() CLK, DIN, DOUT CS ADT, ADuM1311 GND INT, CT ADT7310 CS ADT, INT, CT TO SDP-B CH1: 6-PIN TERMINAL BLOCK FOR FURTHER COST SAVING AVDD AVDD 5V +15V 15V (AVDD/DVDD) 0.1F 0.1F ADP1720 AVDD DVDD AD8226 R9 ADR441 AD7795 10k INA1 15V +15V AIN1+ R2 2.5V R10 2. 2k REFIN2(+) V1+ 2k R6 R7 AIN1 1M 1M R3 R5 REFIN2() V 2.5V 2. 2k V1 D1 2. 2k IOUT1 R1 R13 249 I1 2. 2k AIN2+ ADuM3471 R12 V+ 2. 2k AIN2 R8 V CS D2 2. 2k R4 CLK IOUT2 2. 2k Vm DIN REFIN1(+) DOUT R11 4. 75k P1 REFIN1() CS ADT GND ADT7310 CLK, DIN, DOUT Figure 3. Functional Block Diagram (Simplified Schematic: All Connections and Decoupling Not Shown) Digital and power isolation is achieved using ADuM3471, a CIRCUIT DESCRIPTION PWM controller and transformer driver with quad-channel The AD7795 low noise, 16-bit, - ADC with on-chip in-amp isolator which is used to generate an isolated 15 V supply and reference is used for the data conversion. The on-chip in-amp using an external transformer. The ADuM1311, triple-channel and current sources provide a complete solution for RTD and digital isolator is also used in the 4-pin terminal block circuit to thermocouple measurement. For the voltage and current inputs, isolate the control lines for the ADG442 switches. the AD8226 instrumentation amplifier with >90 dB CMRR is used The ADP2441, 36 V step-down dc-to-dc regulator has a wide to provide a high input impedance and reject any common-mode tolerance on its input supply making it ideal for accepting a interference. The voltage and current signals are scaled to the 24 V industrial supply. It accepts up to 36 V, thereby making range of the ADC using a precision resistor divider. reliable transient protection of the supply input more easily The ADR441, an ultralow noise, low dropout XFET 2.5 V achievable. It steps the input voltage down to 5 V to power the voltage reference is used as the reference for the ADC. ADuM3471 as well as all other controller-side circuitry. The For the 4-pin terminal block channel (CH2), the ADG442, low circuit also includes standard external protection on the 24 V R , latch-up proof switch is used to switch between voltage, ON supply terminals. current, thermocouple, and RT D input modes. Rev. 0 Page 2 of 13 11462-003