Circuit Note CN-0364 Devices Connected/Referenced Low Power, 8-/16-Channel, 31.25 kSPS, AD7173-8 24-Bit, Highly Integrated - ADC Low Power HART Modem with AD5700-1 Internal Oscillator Circuits from the Lab reference designs are engineered and Dual-Channel Isolator with Integrated tested for quick and easy system integration to help solve todays ADuM5211 DC-to-DC Converter analog, mixed-signal, and RF design challenges. For more 3.75 kV, 7-Channel, SPIsolator Digital information and/or support, visit www.analog.com/CN0364. ADuM3151 Isolator for SPI CMOS, Low Voltage, 4 , 4-Channel ADG704 Multiplexer 36 V, 1 A, Synchronous, Step-Down ADP2441 DC-to-DC Regulator PLC/DCS Quad Channel Voltage and Current Input with HART Compatibility components and result in additional space savings. The four EVALUATION AND DESIGN SUPPORT programmable general-purpose output pins (GPIO0, GPIO1, Circuit Evaluation Boards GPO2, GPO3) allow external multiplexer control, which allows CN-0364 Circuit Evaluation Board (EVAL-CN0364-SDPZ) the control of the multiplexed HART interface and eliminates System Demonstration Platform (EVAL-SDP-CB1Z) the need for additional control lines from the processor/controller. Design and Integration Files The AD7173-8 has internal calibration registers that can be Schematics, Layout Files, Bill of Materials programmed to provide offset and gain corrections for the full CIRCUIT FUNCTION AND BENEFITS input path. The circuit shown in Figure 1 provides a complete, fully isolated, The AD5700-1 is the industrys lowest power and smallest footprint highly flexible, quad channel analog input system suitable for HART-compliant modem and is used in conjunction with the programmable logic controllers (PLCs) and distributed control current input channels to form a HART-compatible, 4 mA to system (DCS) applications that require multiple voltage inputs 20 mA receiver solution. The AD5700-1 includes a precision and HART-compatible, 4 mA to 20 mA current inputs. internal oscillator that provides additional space savings, especially in isolated applications. The analog input circuit is designed for group isolated industrial analog inputs and can support voltage and current input ranges The ADG704 multiplexer provides HART connectivity to the including 5 V, 10 V, 0 V to +5 V, 0 V to +10 V, +4 mA to multiple current input channels. +20 mA, and 0 mA to +20 mA. The ADuM5211 isolates two data channels (Tx, Rx) and also The circuit is powered from a standard 24 V bus supply and provides the 5 V power isolation via integrated isoPower generates an isolated 5 V system supply voltage. technology. The ADuM3151 SPIsolator provides serial peripheral interface (SPI) isolation at clock rates of up to CIRCUIT DESCRIPTION 17 MHz (B grade), as well as isolating three additional data The data conversion is performed by the AD7173-8 24-bit, - channels. analog-to-digital converter (ADC). The AD7173-8 is software The ADP2441 36 V, step-down, dc-to-dc regulator accepts an configurable and allows 8 fully differential or 16 single-ended industrial standard 24 V supply, with wide tolerance on the input input channels, offering great flexibility via an internal crosspoint voltage. The ADP2441 steps the input voltage down to 5 V to multiplexer. The AD7173-8 is in a small 6 mm 6 mm LFCSP power all controller side circuitry. The circuit also includes package, making it ideal where space is a premium. The internal standard external protection on the 24 V supply terminals. clock and precision 2.5 V voltage reference minimize external 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 2014 Analog Devices, Inc. All rights reserved. CN-0364 Circuit Note +5V ISO +5V ISO VIO AVDD1 AVDD2 ADuM3151 AIN14 V V DD2 V+ DD1 CHANNEL 1 CH 1 CH 1 VOLTAGE INPUT VOLTAGE NETWORK V AIN15 SCLK SCLK MCLK SCLK DIN SI MO SDI FAST I SPI AIN0 I+ CHANNEL 1 DOUT SO MI SDO CH 1 iCOUPLER CH 1 CURRENT INPUT CURRENT SLOW I CORE NETWORK GND AIN1 CS SSS MSS CS V V OA IA AD7173-8 V+ CH 2 V V IC OC V AIN8 +5V ISO GND CH 4 2 GND 1 I+ VOLTAGE ADG704 AIN9 CH 2 RTS GND VIO +5V ISO AIN2 CH 4 CD V ADuM5211 V DD2 DD1 CURRENT UART V+ AIN3 GPIOx DGND V V RX CH 3 AVSS IA OA 2-2 CHANNEL 4 V 1 OF 4 iCOUPLER DECODER CORE V V TX +5V ISO OB IB I+ GPIOx 4 5.5V CH 3 TO +5V ISO AD5700-1 36V +5V ISO +5V GND RTS V V HART ISO DDP OUTPUT HART OUT ADG704 NETWORK CD ADP2441 V+ isoPOWER DC-TO-DC DC-TO-DC FIELD CH 4 HART CONVERTER SUPPLY ADC IP CONVERTER OUTPUT RXD V CIRCUIT NETWORK REF TXD I+ GND GND P ISO CH 4 1 OF 4 AGND DGND DECODER GND ISOLATED PROCESSOR GPIOx 4 SIDE SIDE Figure 1. PLC/DCS Quad Channel Voltage and Current Input Front End (Simplified Schematic: All Connections and Decoupling Not Shown) Voltage Input Circuit the circuit. Single point calibration is recommended to remove the initial errors. Multipoint calibration can be used to cancel Figure 2 shows the voltage input network for Channel 1. temperature drift effects. The board is populated by default with R1 0.1%, 25 ppm/C resistors for R1, R2, R3, and R4. 402k +2.0V 1.1V V+ AIN14 0V 10V V (5V) The R5 and R6 resistors set the common-mode voltage for the DD R3 C1 R5 ADC. The AD7173-8 has an allowable input voltage range of 49.9k 16pF 4.99k C3 +2.2V 0 V to 3.9 V. The bias voltage of +2.2 V, along with the input 82pF divider resistors, level shifts and attenuates the 10 V input R4 C2 R6 49.9k 16pF 4.02k signal to 1.1 V centered on a common-mode voltage of +2 V R2 402k at the ADC input. V AIN15 Figure 2. Voltage Input Equivalent Circuit (Simplified) Input common-mode noise filtering is provided by R1 R3/C1 and R2 R4/C2, and is approximately 200 kHz. Differential The circuit has differential inputs and supports an input range noise filtering is provided by R1 R3, R2 R4, and C3, and is of up to 10 V with up to 5 V common-mode voltage. The approximately 20 kHz. input impedance is ~900 k, and the high values of R1 and R2 also protect the input during any high voltage transient events. Table 1 summarizes the parameters of the four voltage input channels. The R1, R2, R3, and R4 resistors form a differential resistor divider. The matching of these resistors is critical to the dc accuracy of Rev. 0 Page 2 of 6 12592-002 12592-001