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Optically Isolated Sigma-Delta Modulator ACPL-796J

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Overview Study on Optically isolated Sigma-Delta Modulator

Overview Study on Optically isolated Sigma-Delta Modulator

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  • This is a training module on the Avago Technologies optically isolated sigma-delta modulator ACPL-796J
  • Welcome to the training module on ACPL-796J. This training module gives you an overview introduction to features and applications of the Sigma-Delta Modulator.
  • The ACPL-796J is a 1-bit, second-order sigma-delta (Σ-Δ) modulator which converts an analog input signal into a high-speed data stream with galvanic isolation based on optical coupling technology. The ACPL-796J operates from a 5 V power supply with dynamic range of 80 dB with an appropriate digital filter. The differential inputs of ±200 mV (full scale ±320 mV) are ideal for direct connection to shunt resistors or other low-level signal sources in applications such as motor phase current measurement.
  • The ACPL-796J is ideal for use in industrial applications such as HVAC systems, conveyors, servo motors and a wide range of industrial automation applications.
  • The ACPL-796J is designed with digital inputs and outputs that are compatible with systems powered by 5- or 3-volt supplies and works under a wide industrial temperature range. With 0.5 mm minimum distance through insulation, the ACPL-796J provides reliable double protection and high working insulation voltage, which is suitable for fail-safe designs. Based on an advanced low power CMOS process, the ACPL-796J uses an external clock that allows synchronized data conversion between the current sensor and controller to help motor control designers eliminate complex design processes in data and clock reading. Moreover, the ACPL-796J is designed with digital inputs and outputs that are compatible with systems powered by 5- or 3-volt supplies and works under a wide industrial temperature range.
  • The main function of the modulator (opto coupler) is to provide galvanic isolation between the analog signal input and the digital data output. modulator delivering high noise margins and excellent immunity against isolation-mode transients. With 0.5 mm minimum distance through insulation, The analog input is continuously sampled by means of sigma-delta over-sampling using external clock, coupled across the isolation barrier, which allows synchronous operation with any digital controller. The signal information is contained in the modulator data, as a density of ones with data rate up to 20 MHz, and the data are encoded and transmitted across the isolation boundary where they are recovered and decoded into high-speed data stream of digital ones and zeros. The original signal information can be reconstructed with a digital filter. The serial interface has a wide supply range of 3 V to 5.5 V.
  • In this page some of the important definitions relevant to Sigma-Delta modulators have been defined. They are Integral Nonlinearity (INL), Differential Nonlinearity (DNL), Offset Error, Signal-to-Noise Ratio (SNR).
  • This is in continuation to the previous page here the definitions of Signal-to-(Noise + Distortion) Ratio (SNDR), Effective Number of Bits (ENOB), Isolation Transient Immunity (CMR) have been explained.
  • The differential analog inputs of the ACPL-796J are implemented with a fully-differential, switched-capacitor circuit. The ACPL-796J accepts signals of ±200 mV (full scale ±320 mV), which is ideal for direct connection to shunt based current sensing or other low-level signal sources applications such as motor phase current measurement. An internal voltage reference determines the full-scale analog input range of the modulator (±320 mV); an input range of ±200 mV is recommended to achieve optimal performance.
  • This page shows the typical performance curve of the modulator device. Input current verses input voltage and Signal-to-(Noise + Distortion) Ratio verses input voltage has been shown.
  • The ACPL-796J Isolated Modulator (opto coupler) uses sigma-delta modulation to convert an analog input signal into a high-speed single-bit digital data stream,the time average of the modulator’s single-bit data is directly proportional to the input signal. This evaluation board allows direct modification to the interface IC in order to achieve different levels of performance. It also has a real-time display of the converted data on the terminal screen.
  • A typical three-phase induction motor drive shown here first rectifies and filters the three-phase AC line voltage to obtain a high-voltage DC power supply. The output transistors then invert the DC supply voltage back into an AC signal to drive the three-phase induction motor. The motor drive commonly uses pulse-width modulation (PWM) to generate a variable voltage, variable frequency drive signal for the motor. High performance motor drives usually incorporate some form of current sensing in their design.
  • In the typical application circuit shown here, the ACPL-796J is connected in a single-ended input mode. Given the fully differential input structure, a differential input connection method is recommended to achieve better performance. The voltage from the current sensing resistor or shunt (RSENSE) is applied to the input of the ACPL-796J through an RC anti-aliasing filter (R2 and C2). And finally, a clock is connected to the ACPL-796J and data are connected to the digital filter. The input currents created by the switching actions on both of the pins are balanced on the filter resistors and cancelled out each other. Any noise induced on one pin will be coupled to the other pin by the capacitor C and creates only common mode noise which is rejected by the device.
  • Thank you for taking the time to view this presentation on “ ACPL-796J” . If you would like to learn more or go on to purchase some of these devices, you may either click on the part list link, or simply call our sales hotline. For more technical information you may either visit the Avago Technologies site, or if you would prefer to speak to someone live, please call our hotline number, or even use our ‘live chat’ online facility. You may visit Element 14 e-community to post your questions.
  • Transcript

    • 1. Optically Isolated Sigma-Delta Modulator ACPL-796J
      • Source: Avago Technologies
    • 2. Introduction
      • Purpose
        • Overview Study on Optically isolated Sigma-Delta Modulator.
      • Outline
        • Features Application and its Benefits.
        • Block Diagram of ACPL -796J device.
        • Analog Inputs and its Parameters.
        • Typical Performance Plots.
        • Evaluation Kit and few of Application circuits.
      • Content
        • 14 pages
    • 3. Features
      • 5 to 20 MHz external clock input range.
      • 1-bit, second order sigma-delta modulator.
      • 16-bit resolution (12-bit effective resolution).
      • 74 dB minimum SNR.
      • 3.5 µV/degrees C maximum offset drift.
      • ± 1% maximum gain error.
      • ± 200 mV linear range with single 5V supply (±320 mV full scale).
      • 3 to 5.5V wide supply range for digital I/O.
      • 25 kV/µs Common-Mode transient immunity.
      • Operating temperature range: -40 to 105 degrees C.
      • Worldwide industrial safety approvals: IEC/EN/DIN
      • EN 60747-5-2, UL 1577 and CSA.
      • 5 to 20 MHz external clock input range.
      • 1-bit, second order sigma-delta modulator.
      • 16-bit resolution (12-bit effective resolution).
      • 74 dB minimum SNR.
      • 3.5 µV/degrees C maximum offset drift.
      • ± 1% maximum gain error.
      • ± 200 mV linear range with single 5V supply (±320 mV full scale).
      • 3 to 5.5V wide supply range for digital I/O.
      • 25 kV/µs Common-Mode transient immunity.
      • Operating temperature range: -40 to 105 degrees C.
      • Worldwide industrial safety approvals: IEC/EN/DIN
      • EN 60747-5-2, UL 1577 and CSA.
    • 4. Applications
      • Motor phase and rail current sensing.
      • Power inverter current and voltage sensing.
      • Industrial process control.
      • Data acquisition systems.
      • General purpose current and voltage sensing.
      • Traditional current transducer replacements.
    • 5. Benefits of ACPL-796J
      • Modulator using external clock enables synchronized data conversion.
      • Auto-insertable SO-16 package smaller than conventional current transducers.
      • High CMR capability provides smoother motor control.
      • Advanced sigma-delta converter technology provides precision, stability and reliability in motor control.
      • Low offset voltage, low gain error and high linearity.
      • Meets worldwide safety approvals: UL 1577, CSA and IEC/EN/DIN EN 60747-5-5.
    • 6. Block Diagram of ACPL-796J
      • The modulator delivers high noise margins and excellent immunity against isolation-mode transients.
      • The analog input is continuously sampled by means of sigma-delta over-sampling using external clock, coupled across the isolation barrier.
      • The data are encoded and transmitted across the isolation boundary where they are recovered and decoded into high-speed data stream of digital ones and zeros.
    • 7. Parameters of Sigma-Delta Modulator
      • Integral Nonlinearity (INL):
      • INL is the maximum deviation of a transfer curve from a straight line passing through the endpoints of the ADC transfer function, with offset and gain errors adjusted out.
      • Differential Nonlinearity (DNL)
      • DNL is the deviation of an actual code width from the ideal value of 1 LSB between any two adjacent codes in the ADC transfer curve.
      • A DNL error of less than ±1 LSB guarantees no missing codes and a monotonic transfer function.
      • Offset Error
      • Offset error is the deviation of the actual input voltage corresponding to the mid-scale code from 0 V.
      • Signal-to-Noise Ratio (SNR)
      • The SNR is the measured ratio of AC signal power to noise power below half of the sampling frequency. The noise power excludes harmonic signals and DC.
    • 8. Parameters of Sigma-Delta Modulator
      • Signal-to-(Noise + Distortion) Ratio (SNDR)
      • The SNDR is the measured ratio of AC signal power to noise plus distortion power at the output of the ADC.
      • The signal power is the RMS amplitude of the fundamental input signal.
      • Noise plus distortion power is the RMS sum of all non-fundamental signals up to half the sampling frequency (excluding DC).
      • Effective Number of Bits (ENOB)
      • The ENOB determines the effective resolution of an ADC, expressed in bits, defined by ENOB = (SNDR − 1.76)/6.02.
      • Isolation Transient Immunity (CMR)
      • The isolation transient immunity (also known as Common-Mode Rejection or CMR) specifies the minimum rate-of-rise/fall of a common-mode signal applied across the isolation boundary beyond which the modulator clock or data is corrupted.
    • 9. Analog Input Differential input connection diagram Analog input equivalent circuit
      • The differential analog inputs of the ACPL-796J are implemented with a fully-differential, switched-capacitor circuit.
      • The ACPL-796J accepts signal of ±200 mV (full scale ±320 mV), which is ideal for direct connection to shunt based current sensing.
      • An internal voltage reference determines the full-scale analog input range of the modulator (±320 mV).
    • 10. Typical Performance Plots Input current vs. input voltage. SNDR vs. input voltage VIN. TA = 25°C, VDD1 = 5 V, VDD2 = 5 V, VIN+ = –200 mV to +200 mV, and VIN– = 0 V, Fmclkin = 10 MHz, with Sinc3 filter, 256 decimation ratio.
    • 11. Opto-Isolated A/D Converter Evaluation Kit ACPL-796J and HCPL-0872 Evaluation Kit
    • 12. Isolation Amplifiers Typical Three-Phase AC Induction Motor Drive
    • 13. Digital Current Sensing Circuit Typical application circuit for motor phase current sensing
      • By choosing the appropriate shunt resistance, any range of current can be monitored, from less than 1 A to more than 100 A.
      • The input currents created by the switching actions on both of the pins are balanced on the filter resistors and cancelled out each other.
    • 14. Additional Resource
      • For ordering ACPL-796J, please click the part list or
      • Call our sales hotline
      • For more product information go to
        • http://www.avagotech.com/pages/en/optocouplers_plastic/plastic_miniature_isolation_amplifier/acpl-796j-000e/
      • Visit Element 14 to post your question
        • www.element-14.com
      • For additional inquires contact our technical service hotline or even use our “Live Technical Chat” online facility

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