EVAL-CN0292-SDZ

Circuit Note CN-0292 Devices Connected/Referenced Circuits from the Lab® reference designs are engineered and tested for quick and easy system integration to help solve today’s analog, mixed-signal, and RF design challenges. For more information and/or support, visit www.analog.com/CN0292. AD7176-2 24-Bit, 250 kSPS, Σ-Δ ADC with 20 μs Settling AD8475 Precision, Selectable Gain, Fully Differential Funnel Amplifier ADR4550 Ultralow Noise, High Accuracy, 5.0 V Voltage Reference ADuM3471 Isolated Switching Regulators (3/1 Channel Directionality) ADP7102 20 V, 300 mA, Low Noise, CMOS LDO Regulator ADA4898-1 High Voltage, Low Noise, Low Distortion, Unity Gain Stable, High Speed Op Amp ADP7182 −28 V, 200 mA, Low Noise, Linear Regulator ADA4096-4 ADG1204 ADP1720 30 V, Micropower, Overvoltage Protection, RRIO, Quad Op Amp Low Capacitance, Low Charge Injection, iCMOS®, ±15 V/±12 V, 4:1 Multiplexer 50 mA, High Voltage, Micropower Linear Regulator Completely Isolated, Robust, 4-Channel, Multiplexed Data Acquisition System for Industrial Level Signals EVALUATION AND DESIGN SUPPORT Circuit Evaluation Boards CN-0292 Circuit Evaluation Board (EVAL-CN0292-SDZ) System Demonstration Platform, SDP-B (EVAL-SDP-CB1Z) Design and Integration Files Schematics, Layout Files, Bill of Materials CIRCUIT FUNCTION AND BENEFITS The circuit in Figure 1 is a completely isolated, robust, industrial, 4-channel data acquisition system that provides 16-bit, noise free code resolution and an automatic channel switching rate of up to 42 kSPS. The channel to channel crosstalk at 42 kSPS switching is less than 15 ppm FS (less than −90 dB) because of the unique selection of fast settling components in the multiplexed signal chain. The circuit acquires and digitizes standard industrial signal levels of ±5 V, ±10 V, 0 V to 10 V, and 0 mA to 20 mA. The input buffers also provide overvoltage protection, thereby eliminating the leakage errors associated with conventional Schottky diode protection circuits. Applications for the circuit include process control (PLC/DCS modules), battery testing, scientific multichannel instrumentation, and chromatography. 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 determining its suitability and applicability for your use and application. Accordingly, in no event shall Analog Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due toanycausewhatsoeverconnectedtotheuseofanyCircuitsfromtheLabcircuits. (Continuedonlastpage) One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2014 Analog Devices, Inc. All rights reserved. CN-0292 Circuit Note +16.76V +V_ISO TRANSFORMER 100kΩ +V_ISO SCHOTTKY DIODE FULL WAVE RECTIFIER +15V_REG VIN VOUT ADP7102 8.06kΩ 11.3kΩ ADJ 1kΩ –V_ISO GND +15V_REG ADA4096-4 +15V_REG ADG1204 –V_ISO 47Ω CH1 10nF –15V_REG +15V_REG VIN +5V_REG VOUT ADP7182 IN 11.3kΩ V2 10Ω 47nF 1.8kΩ –15V_REG 47nF 47Ω CH4 10nF +15V_REG 270pF 1kΩ 10Ω +IN 0.4× 680pF –IN ADA4898-1 0.4× V4 10Ω +5V_REG AD8475 2.5kΩ 68pF 47Ω CH3 10nF +15V_REG 2.5kΩ 270pF 1kΩ VOCM 47nF –15V_REG 10kΩ +2.5V EN A0 A1 X2 VDD2 +5V_EXT VDD1 VDDA VOUT GND2 GND1 ADR4550 GND2 GND1 GND_EXT GND +5V AVDD1, AVDD2 AIN1 AIN0 10Ω X1 FB OC VIN GND +5V_REG 47Ω V3 10Ω 100kΩ +15V_REG 1kΩ GND CH2 10nF OUT ADP7182 ADJ 47nF +5V_REG VREG ADuM3471 REF+ AD7176-2 DGND AVSS CS SCLK DIN DOUT VOA VOB VOC VID VIA VIB VIC VOD SPI ISOLATED SIDE PROCESSOR SIDE 10976-001 V1 10Ω +1.25V REFOUT GPIO0 GPIO1 ±10V INPUTS –15V_REG Figure 1. Functional Block Diagram of 4-Channel Data Acquisition System (Simplified Schematic: All Connections and Decoupling Not Shown) VIN CH1 Signal Path +FS C Four channels of input signals are buffered by the ADA4096-4, a quad, rail-to-rail, input/output op amp featuring overvoltage protection against phase reversal or latch-up for inputs of up to 32 V above or below the ±15 V supply rails, which eliminates the need for additional overvoltage protection circuitry. The inputs are designed for typical low frequency, industrial signals of ±10 V. The input buffers provide a high impedance to the sources and isolate the inputs from the multiplexer switching transients. The RC networks on the inputs of the buffers (10 Ω/10 nF) have a bandwidth of 1.6 MHz and provide high frequency noise filtering. The RC networks on the outputs of the ADA4096-4 (47 Ω/47 nF) isolate the buffers from the multiplexer switching transients. Figure 2 shows an equivalent circuit. The drain capacitor, CD, must be charged by the input voltage before switching to the next channel. There can be as much as 20 V between channels, and a transient current is generated when the multiplexer switches to the next channel. R VIN CH2 –FS VOUT CD R +FS –FS C 10976-002 CIRCUIT DESCRIPTION Figure 2. RC Kickback Isolation Circuit The ADG1204 multiplexer, featuring low drain capacitance (