Circuits from the Lab Reference Designs Precision Data Acquisition About Circuits from the Lab Reference Designs ADI Circuits from the Lab® Reference Designs are built and tested for function and performance by ADI’s applications experts. Circuits from the Lab support quick and easy evaluation, prototyping, and design integration, and offer: • Comprehensive documentation • Complete design and integration files • Factory tested evaluation hardware Precision Data Acquisition Circuits from the Lab Reference Designs are application agnostic and are commonly used in analog signal chain design as standalone solutions, or to build more complex circuits and subsystems. Precision Data Acquisition Application Introduction Precision data acquisition systems (DAQs) are essential to many medical, industrial, instrumentation, and military applications. Resolution requirements range from 16 bits to 24 bits, and sampling rates from a few Hz to several MHz. In multichannel systems, analog multiplexers allow a single analog-to-digital converter (ADC) to sample a number of channels, thereby lowering cost and printed circuit board real estate. Choosing the proper ADC is an important design consideration, as well as the supporting circuitry, including the voltage reference, input drive amplifier, instrumentation amplifier, multiplexer, and power supply. Design Considerations and Major Challenges Successive approximation (SAR) and sigma-delta (Σ-Δ) are the most popular ADC architectures for data acquisition systems. However, choosing the correct architecture for an application can be a challenging task. Successive approximation ADCs are available with resolutions of up to 18 bits and sampling rates of several MSPS (see CN0277 that highlights the AD7960 18-bit, 5 MSPS ADC). They are ideal for multiplexed applications requiring a large number of channels (see CN0254 and CN0269). SAR ADCs find widespread applications in medical imaging, electronic test and measurement, and industrial applications such as programmable logic controllers (PLCs) and distributed control systems (DCSs). Σ-Δ ADCs have resolutions up to 24 bits and are ideal for precision measurement applications that use low sampling rates (see CN0251 and CN0310). High resolution allows a direct interface to many sensors such as thermocouples, load cells, and RTDs. Some Σ-Δ ADCs have internal programmable gain amplifiers that facilitate processing low level signals without the requirement for additional gain components. The design of a DAQ can be quite challenging because of the many trade-offs possible. For example, industrial signals of ±10 V require special conditioning to interface with single-supply differential input ADCs (see CN0251, CN0269, and CN0310). Harsh industrial environments may also require high voltage digital isolators to protect sensitive circuits (see CN0254). Making the proper trade-offs between power dissipation, dynamic performance, PCB area, and cost is important for a competitive design, and achieving required performance depends on careful attention to layout, grounding, and decoupling techniques. www.analog.com/circuits-from-the-lab Circuits from the Lab Reference Designs—Precision Data Acquisition Circuits from the Lab Reference Designs CN0310 Resolution (Bits) Sampling Rate (kSPS) Number of Channels Converter Architecture Input Signal Range (V) Power Dissipation (mW) Data Output Format 24 250 1 Σ-Δ ±10, ±5, 0 to +10 54 Evaluation Hardware Pricing ($/ea) SPI EVAL-AD7176-2SDZ* 59.00 130 SPI EVAL-CN0251-SDPZ* 80.00 EVAL-AD7960FMCZ** 99.00 EVAL-CN0269-SDPZ* 100.00 EVAL-CN0261-SDPZ* 79.00 EVAL-CN0305-SDPZ* 99.00 CN0251 24 4.7 Hz 4 Σ-Δ ±10, ±5, ±1, ±500 mV, ±250 mV, ±125 mV, ±62, 5 mV, ±31.25 mV CN0277 18 5 MSPS 1 PulSAR® 0 to +5 122 LVDS CN0269 18 1.33 MSPS 16 PulSAR ±10, ±5 337 SPI CN0261 18 250 1 PulSAR 0 to +5 107 SPI CN0305 16 300 1 PulSAR 0 to +5 11 SPI CN0254 16 250 8 PulSAR ±10 294 SPI CN0306 16 100 1 PulSAR 0 to +5 7.4 SPI CN0255 16 100 1 PulSAR Additional Features 8 0 to +2.5 SPI Optimized for ac performance Optimized for ac performance Optimized for sub-Nyquist input signals up to 4 kHz Isolated Optimized for sub-Nyquist input signals up to 4 kHz EVAL-CN0254-SDPZ* 75.00 EVAL-CN0306-SDPZ* 99.00 EVAL-CN0255-SDPZ* 79.00 * This reference design also requires EVAL-SDP-CB1Z ($99.00) ** This reference design also requires EVAL-SDP-CH1Z ($199.00) Highlighted Circuits from the Lab Reference Designs +7V +5V SINGLE ENDED +5V +12V VDD AI0 AI1 AI2 AI3 AI4 AI5 AI6 AI7 S1 S2 S3 S4 S5 S6 S7 S8 AI0+ AI1+ AI2+ AI3+ AI4+ AI5+ AI6+ AI7+ –12V VSS GND P4 AGND +12V EN A0 A1 A2 ADG5208 –12V VDD GND S1A S1B S2A S2B NC_1 NC_2 NC_3 +12V VDD AI8 AI9 AI10 AI11 AI12 AI13 AI14 AI15 S1 S2 S3 S4 S5 S6 S7 S8 AI0– AI1– AI2– AI3– AI4– AI5– AI6– AI7– –12V DIFFERENTIAL VSS GND D NC_4 NC_5 ADG5236 1.25kΩ 2 –IN_0.4* –12V +12V –12V 1kΩ 0.1µF 1.25kΩ 3 –IN_0.8* VCOM 3 +IN_0.8* 2 +IN_0.4* 1 JP4 +VS 1.25kΩ 1.25kΩ NC 1kΩ +OUT –OUT VIO 10kΩ 10Ω 2.2nF IN+ 2.2nF REF VDD IN– 10Ω GND AD8475 ADG5208 33Ω 33Ω 33Ω Y B A CN0269:18-bit, 1.33 MSPS, 16-channel data acquisition system. | Circuits from the Lab Reference Designs 2 74LVC1G00 VCM = VREF ÷ 2 = 2.5V VIO SDI SCK SDO CNV 33Ω 33Ω 33Ω TCLKBF DATA TFS VREF = 5V CP 15Ω 0.1µF PL U/D P0 P1 P2 P3 P0 P1 P2 P3 S_D EN IN+ CNV+/ CNV– 100Ω VCM = VREF ÷ 2 = 2.5V VIN– 0.1µF 820Ω GND 56pF ADA4897-1 0.1µF DCO+/DCO– IN– 33Ω 100pF 1kΩ 100Ω D+/D– AD7960 +VS +7V/+5V/EXT 0.1µF 74LVC169 REFIN REF VDD1 VDD2 VIO ADA4897-1 0.1µF –2.5V/EXT –VS VIN– GPIO PE U/D 56pF VIN+ GND Q0 Q1 Q2 Q3 33Ω 1kΩ VCM = 2.5V AD7984 VCC GND CEP CET TC +5V +1.8V 820Ω 100pF +3.3V 33Ω 33Ω 33Ω VIN+ SPORT –VS AD8065 CH0 CH1 CH2 CH3 EN A0 A1 A2 +VS +7V/+5V/EXT 0.1µF 0Ω VCOM JP3 1 1kΩ 1kΩ 0.1µF 50V 22µF 6.3V +5V +12V IN2 0.1µF 50V ADR4550 +2.5V +4.096V TP_2 NC_2 VOUT TRIM ADR444 1kΩ IN1 D2 DGND AD8065 VSS D1 TP_1 VIN NC_1 GND 0.1µF 50V D +7V +5V AD8031 VCM CLK+/CLK– 100Ω 100Ω +2.5V +7V AD8031 –2.5V/EXT –VS CN0277: high precision, 18-bit, 5 MSPS, low power data acquisition signal chain. Key Products Analog-to-Digital Converters Resolution (Bits) Throughput Rate Max (kSPS) Architecture Full Power BW (MHz) Number of Channels Package AD7176-2 24 250 4 TSSOP 24 18 18 18 16 16 16 4.8 5 MSPS 250 1.33 MSPS 250 500 100 Σ-Δ Σ-Δ N/A AD7192 AD7960 AD7691 AD7984 AD7689 AD7988-5 AD7988-1 N/A 28 2 10 1.7 10 10 4 1 1 1 8 1 1 TSSOP LFCSP MSOP, LFCSP MSOP, LFCSP LFCSP MSOP, LFCSP MSOP, LFCSP Part Number PulSAR PulSAR PulSAR PulSAR PulSAR PulSAR Rail-to-Rail Output Fully Differential Funnel Amplifier Part Number ∙3 dB BW (MHz) Slew Rate (V/𝛍s) Closed-Loop Gain Input Offset Voltage (𝛍V) Min Pos Supply (V) Max Pos Supply (V) Supply Current per Amplifier (mA) Amplifiers per Package Package 150 50 0.4, 0.8 200 3 10 3 1 MSOP, LFCSP AD8475 Rail-to-Rail Output Instrumentation Amplifier Part Number Gain (Min) Gain (Max) Min CMRR @ 60 Hz, G = 1 (dB) VSUPPLY Span Min (V) VSUPPLY Span Max (V) Supply Current (𝛍A) Voltage Noise RTI (𝛍V p-p) Package 1 1000 86 2.2 36 400 2 MSOP, SOIC AD8226 Operational Amplifiers Small Signal Bandwidth (MHz) Slew Rate (V/𝛍s) Input Offset Voltage (𝛍V) Amplifiers per Package VSUPPLY Span Min (V) AD8031 80 35 1 mV 1 2.7 12 Input, output 0.9 AD8032 80 35 1 mV 2 2.7 12 Input, output 0.9 ADA4897-1 ADA4897-2 230 230 120 120 28 28 1 2 3 3 10 10 Output Output 3 3 AD8065 145 180 400 1 5 24 Output 6.4 Part Number VSUPPLY Span Rail-Rail Supply Current Max (V) Input/Output per Amplifier (mA) Package PDIP, SOIC, SOT-23 PDIP, SOIC, MSOP SOIC, SOT-23 MSOP MSOP, SOIC, SOT-23 AD8597 10 14 10 1 10 36 4.8 SOIC, LFCSP OP1177 AD8605 AD8608 AD8609 AD8641 1.3 10 10 400 kHz 3.5 0.7 5 5 0.1 3 15 20 20 12 50 1 1 4 4 1 5 2.7 2.7 1.8 5 36 6 6 5 26 Input, output Input, output Input, output Output 0.4 1 1 0.05 0.25 MSOP, SOIC SOT-23, WLCSP SOIC, TSSOP SOIC, TSSOP SC70, SOIC 80 13 40 1 2.7 12 Output 1.1 SOT-23, SOIC ADA4841-1 Voltage References Part Number ADR445 ADR444 ADR4550 ADR435 ADR4525 VOUT (V) 5 4.096 5 5 2.5 Initial Accuracy (%) 0.04 0.04 0.02 0.04 0.02 Ref Out TC (ppm/∙C) 1 1 2 1 2 0.1 Hz to 10 Hz Noise (𝛍V p-p) 2.25 1.8 2.8 8 1.25 Reference Type Max Input Voltage (V) Series low dropout Series low dropout Series low dropout Series Series low dropout 18 18 15 18 15 Dropout Voltage (mV) 500 500 300 2V 300 Package MSOP, SOIC MSOP, SOIC SOIC MSOP, SOIC SOIC isoPower Digital Isolators Part Number ADuM3471 Number of Inputs Side 1 Number of Inputs Side 2 3 1 Insulation Rating (kV rms) 2.5 Max Data Rate (Mbps) Prop Delay (ns) Isolated Output Supply (mA) Isolated Output Voltage Min/ Max (V) Max Pos Supply (V) Package 25 60 400 3.3/24 5.5 SSOP www.analog.com/circuits-from-the-lab | 3 Linear Regulators Part Number ADP1720 ADP3336 VIN Min (V) VIN Max (V) VOUT Preset Max VOUT Adj (V) Min VOUT Adj (V) IOUT (Max) (mA) 4 2.6 28 12 3.3, 5.0 N/A 5 10 1.225 1.5 50 500 Dropout Voltage @ Rated IOUT (mV) 275 200 Package MSOP MSOP Analog Multiplexers Part Number Sw/Mx Function ∙ Number ADG5208 (8:1) × 1 Max Analog Signal Range –3 dB Bandwidth (MHz) Supply V Guar Performance (V) RON (Ω) Transistion Time (ns) Package 54 Dual: (±15), Dual: (±20), Single: (+12), Single: (+36) 160 170 TSSOP, LFCSP 160 150 TSSOP, LFCSP 4 140 TSSOP, LFCSP VSS to VDD ADG5236 (2:1) × 2 VSS to VDD 266 Dual: (±15), Dual: (±20), Single: (+12), Single: (+36) ADG1409 (4:1) × 2 VSS to VDD 115 Dual: (±15), Dual: (±5), Single: (+12) Additional Design Resources Technical Books and Articles Data Conversion Handbook—www.analog.com/library/analogdialogue/archives/39-06/data_conversion_handbook.html • ADC Architectures (Chapter 3.2) • Interfacing to Data Converters (Chapter 6) • Multichannel Data Acquisition Systems (Chapter 8.2) Which ADC Architecture Is Right for Your Application?, Analog Dialogue— www.analog.com/library/analogdialogue/archives/39-06/architecture.html A Practical Guide to High-Speed Printed-Circuit-Board Layout, Analog Dialogue— www.analog.com/library/analogdialogue/archives/39-09/layout.html Tutorials • MT-021: Successive Approximation ADCs—www.analog.com/MT-021 • MT-022: ∑-∆ ADCs—www.analog.com/MT-022 • MT-031: Grounding Data Converters—www.analog.com/MT-031 • MT-101: Decoupling Techniques—www.analog.com/MT-101 Design Tools and Forums • Signal Chain Designer™ Advanced Selection and Design Environment—www.analog.com/signalchaindesigner • EngineerZone™ Online Technical Support Community—ez.analog.com • ADIsimADC™ Converter Modeling Tool—www.analog.com/adisimadc Customer Interaction Center Email North America: [email protected] Europe: [email protected] Asia: [email protected] EngineerZone ©2014 Analog Devices, Inc. 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