Isolated Interface Solutions for Industrial Sensor and Monitoring Applications

Transcription

1 The World Leader in High Performance Signal Processing Solutions Isolated Interface Solutions for Industrial Sensor and Monitoring Applications Michael Müller-Aulmann Applications Engineer icoupler Digital Isolator Group

2 Agenda u Why Isolate Analog Interfaces u Isolated Analog Input Architecture u Powering The Interface u Isolating the Data Path u The Optimal Solution

3 Why Isolate Analog PLC Inputs Transducer u Eliminate ground loops l Offset voltages l Grid noise u Safety l Protection from high transients l Protection from high working voltages u Common mode range l Hundreds of volts ΔV Transducer PGA Filter ADC PGA Filter ADC

4 Typical Isolated Sensor Interface FPGA

5 Typical Isolated Sensor Interface VIN+ VIN- Protection PGA Filter ADC Ch 0 FPGA

6 Typical Isolated Sensor Interface VIN+ VIN- Protection PGA Filter ADC Ch 0 Isolated Power Isolated Data FPGA

7 Typical Isolated Sensor Interface VIN+ VIN- Protection PGA Filter ADC Ch 0 Isolated Power Isolated Data FPGA VIN+ VIN- Protection PGA Filter ADC Ch N Isolated Power Isolated Data

8 Defining the Application u General requirements l 4,8,16 or more channels l Prevent ground loop errors l Safety l Tolerate large common mode voltages u Power requirements l Performance at low power l Regulation l Efficiency at required power u Data path requirements l Adequate SPI bandwidth

9 Isolated Interface Power Requirements Digital Isolator Interface Optocoupler Interface Instrumentation Amp 5mW 5mW Analog to Digital Converter 15mW 15mW Isolation Interface 37mW 118mW Power to a Sensor 5-50mW 5-50mW Total Power mW mW

10 Unregulated Power u Very simple solution l Fixed frequency l Fixed duty cycle l Optimized for max load l Discrete transformer u It can shift expense onto other components l Poor line and load regulation l Unstable operation at very light loads l Large footprint and or height u The design must tolerate sloppy or unstable power

11 Secondary Side Linear Regulation u Next step up in complexity l Good regulation l Integrated wire wound transformer l Fixed frequency l Fixed duty cycle l Optimized for max load u Still not optimum l Large footprint l Wastes power at light loads

12 Chip Scale Power Module u Highly integrated l Fixed frequency l Variable duty factor l Constant efficiency over entire load range l Excellent line and load regulation over the entire load range l Chip scale transformer l Features of brick power supply l Very small solution size u It can shift expense onto other components l Must design for EMI

13 How Chip Scale Converters Work 700mA 125MHz, 700mA Tank Oscillator 150mA 250MHz Rectified Current 5V Regulated output GND1 GNDiso GNDiso u Primary side l PWM controls tank oscillator l During startup tank stays on until output is in regulation VDD1 600kHz PWM Tank Control u Secondary side regulation l Current rectified and filtered l Regulator creates PWM based on selected set point GNDiso

14 Advantages of Working at Light Loads u Chip scale modules have better efficiency at low load u Three cases examined 1. Digital isolation with chip scale power 2. Digital isolation with regulated module 3. Optocouplers with regulated module u Highest solution efficiency achieved in case 1 Efficiency (%) Load Current (ma) DCR01 5V/5V ADuM5010 5V/ 5V Digital Isolator Interface With Chip Scale Converter Digital Isolator Interface With regulated Module Optocoupler Interface With regulated module Instrumentation Amp 1mA 1mA 1mA Analog to Digital Converter 3mA 3mA 3mA Secondary Isolation Interface 7.4mA 7.4mA 23.5mA Through the power supply efficiency Power to a Sensor 1mA 1mA 1mA Primary Isolation Interface 4.5mA 4.5mA 16mA Total Isolated Current 12.5mA 12.5mA 28.5mA Total Input Current 50.8mA 60.9mA 87.3mA

15 Comparison of Power Options Type P/N Peak Effcy. 10mA Effcy. Quiescent Current Max Power Load Reg. Size cost Chip Scale Converter ADuM % 27% 6.8mA 150mW 1.3% 7.4x7.4x2 $1.50 Regulated Module DCR % 21% 18mA 1W 3% 18x10x2.5 $5.95 Unregulated Module DCH % N/A 60mA 1W 10% 20x8x10 $4.25 Unregulated Module Regulated Module Chip Scale Converter

16 Additional Features in Chip Scale Power u Infinitely adjustable output voltage l 3.15 to 5.5V. l Allows margining of supplies u Thermal shutdown l Trips at 154C l 10 C hysteresis l Automatically restart u Soft start l Negligible inrush current u Primary side power disable l Power saving schemes u Under Voltage Lockout (UVLO) l Allows the input supplies pre-charge u Fully certified isolation l Eliminate system level testing

17 Digital Interface u Most ADC s have an SPI type interface u Some are unidirectional only sending a data frame per SS cycle u Some require full bidirectional communication for setup u SPI requirements l Sample rate 256kS l 4MBps l Clock rate 4MHz u Two options l Optocoupler interface l Digital isolator interface

18 Properties of Isolators Optocouplers u Optical transmission u Complex packaging u Difficult to integrate u High input diode drive u Output buffer has high quiescent current u Single direction of isolation within a package Digital Isolators u Magnetic coupling u Standard packaging u Easy to integrate u Low power operation u Mixed transmission direction within a package

19 Choosing a Digital Interface u High-Speed Parameter u Medium-Speed Analog Devices ADuM344x icoupler Avago HCPL-0710 Optocoupler Avago HCPL-0723 Optocoupler Max. Data Rate (Mbps) Prop. Delay (ns) Part to Part Match (ns) Pulse Width Distortion (ns) Parameter Analog Devices ADuM1200BRZ Dual icoupler Avago HCPL-063x Dual Optocoupler Max. Data Rate (Mbps) Prop. Delay (ns) Part to Part Match (ns) Channel-to-Channel Match (ns) 3 unspecified Pulse Width Distortion (ns) 3 35

20 High Speed SPI Interfaces SCLK DIN CSN DOUT Isolator FPGA SCLK MOSI SS1 MISO Maximum SPI Bus Speed 1 2 ( 2 τ ) D + Delay τ D = Propagation Delay Delay = Read/Write Time, Trace Capacitance, etc. SCL K Master side signals MO SI SCL K MO SI MIS O MIS O 1 Dela y 2 Delays Slave side signals u Propagation delay sets maximum speed of the interface l 100 ns propagation delay limits speed to < 5 Mbps

21 icoupler Differential Architecture Edge Encoding Detect Data Edges Encode as Pulses Transfer Through Transformer Decode Pulses Reconstruct Data Rising Edge Falling Edge u Properties of differential encoding u Lower power consumption at high frequency u Higher power consumption at low frequencies u Lower prop delay u Higher data rates u Better noise immunity u Fewer pulses u Lower dive signal to transformer u Lower emissions

22 Error Correction/Failsafe Circuitry u Glitch Filter l Reduces noise l Blocks pulses that are too narrow for the transmitter Glitch Filter Input Refresh DISABLE Encoder Decoder Output SET TIMEOUT Watchdog u Transmit refresh circuitry l Resend data 1µs after the last change on input l Ensures correct data state is transmitted every µs u Receiver watchdog timer l If no pulse received within approximately 3µs, then output is set to default low l Ensures safe output state, if transmitter is not functioning properly

23 Integrating Digital Data Channels u High performance l 100 Mbps l 24 ns propagation delay u Low dynamic power l <16mA / 100 Mbps u Small 8-lead SO u Robust polyimide isolation l 3 kvrms isolation rating l > 50-year lifetime u Easy-to-Use l Digital CMOS input and output u -40 C +125 C

24 Integrated Chip Scale Power u Data isolation can be included in the same packaging as the power u Separate die for data channels allows independent operation of data and power u Future products with differential architecture will include 4 data channels, ideal for SPI interfaces u Independent power supply die allows integration flexibility

25 isopower products ADuM521x ADuM621x ADuM5010 ADuM6010 u Key Features l Adjustable, regulated V ISO : 3.15V to 5.25V l 3.3 or 5V output l Soft-start power supply l Small SSOP package l 0 or 2 icoupler signal channels up to 100 Mbps l Reinforced insulation up to 3.75 kvrms

26 Complete Isolation Solution u Total solution includes l Power for the interface l SPI interface capable of 4mHz u Optocoupler module solution l 400mm 2 PCB space l 438mW total power u Digital isolator interface l 128mm 2 PCB space l 255mW total power u Digital isolation with chip scale power conversion can save l 70% less board space l 40% less power ADuM ADuM1200 HCPL063L + 2ea HCPL060L + DCR010505

27 System Isolation Requirements u Modules and IC s are attractive because they carry certifications that allow l Reduced design time l Streamlined system certification l Elimination of end of line testing u Modules that contain wire wound transformers generally have lower isolation capabilities l Vrms u Chip scale power and data couplers support l 5kV reinforced isolation l 2.5kV basic isolation and can utilize smaller packaging u Typical PLC applications require l Basic 2500Vrms l <400Vrms working voltage

28 Safety Approvals u Certification standards which can be achieved for any icoupler product* l UL 1577 (office equipment) l DIN V VDE V (industrial equipment) l CSA/EN/UL (industrial equipment) l CSA/IEC/EN (information systems) l IEC (medical equipment) u For a list of certifications go to *Specific approvals vary by product

29 What s Not To Love? LAYER 2 GROUND LAYER 3 POWER u EMI can be an issue u 125MHZ high current oscillator can cause PCB emissions u High frequency image charges cannot cross the barrier l Potential difference between grounds on each side of the barrier create a dipole source that radiates u Proper PCB design choices will enable end system to pass CISPR22 Class B and FCC Class B u Application note AN-0971 and ADuM5010 evaluation board user guide are available at OVERLAP CREATING CAPACITANCE

30 What s Not To Love? LAYER 2 GROUND LAYER 3 POWER u EMI can be an issue u 125MHZ high current oscillator can cause PCB emissions u High frequency image charges cannot cross the barrier l Potential difference between grounds on each side of the barrier create a dipole source that radiates u Proper PCB design choices will enable end system to pass CISPR22 Class B and FCC Class B u Application note AN-0971 and ADuM5010 evaluation board user guide are available at OVERLAP CREATING CAPACITANCE

31 Learn More on This Subject

32 Products discussed in this webcast ADuM1200 Dual Channel Digital Isolator ADuM1280 3kV rms, Default High, Dual-Channel Digital Isolators (2/0) ADuM1281 3kV rms, Default High, Dual-Channel Digital Isolators (1/1) ADuM344x Quad Channel, High Speed Digital Isolators ADuM kV rms Isolated DC/DC Converter ADuM5211 Dual-Channel Isolators with Integrated DC/DC Converter (1/1) ADuM kV rms Isolated DC/DC Converter ADuM6210 EVAL-ADUM5010EBZ EVAL-ADUM5211EBZ Dual-Channel Isolators with Integrated DC/DC Converter (2/0) Eval Board for ADuM5010/6010 ($59USD) Eval Board for ADuM521x/621x ($69USD)

33 More Information Available Training and Miscellaneous u Webcast and Training videos l u Circuits from the Lab u Application Notes u Technical Articles u Safety Standards/Certifications Key Application Notes: u AN-825 Power Supply Considerations in icoupler Products u AN-0971 Control of Radiated Emissions with isopower Devices u AN-1109 Control of Radiated Emissions with icoupler Devices u AN-793 ESD/Latch-up Considerations with icoupler Products ez.analog.com/community/interface-isolation