COVER STORY
Isolated gate drivers are also needed to drive high- and low-side power semiconductors to provide robust, safety- compliant and high-reliability assets. The key requirements for gate drivers include high speed, low propagation delay, low delay skew, robustness and common-mode transient immunity, switch protection features (DESAT, Miller clamp, soft shutdown, UVLO) and controllable switching (variable slew rate switching). Standard digital isolators play a role in many drives in transferring signals between high-voltage power electronics domains and safety extra low voltage (SELV) domains for PWM and other signalling. Fully-integrated isolated power solutions can also be combined with digital isolators or other isolated functions to provide signifi cant solution-size reduction compared to a discrete transformer solution.
Industrial Ethernet connectivity with sub-ms cycle times network performance is required for deterministic real-time communication in motion control applications (servos and drives). Robust physical layer devices at 100Mb and Gb speeds combined with Layer-2 Industrial Ethernet protocols such as EtherCAT, PROFINET, EtherNET/IP and IEEE time-sensitive networking (TSN) ensure deterministic Ethernet connectivity. Next- generation designs are moving to Gb TSN on converged networks with multiple traffi c types, cyclic communications for control and acyclic communications for best eff ort traffi c; for example, vision and monitoring traffi c. Low-latency Industrial Ethernet solutions are required to reduce cycle times in multi-axis applications. These deterministic motion solutions enable more complex motion applications that drive higher levels of manufacturing productivity and fl exibility.
Magnetic sensing based on anisotropic magnetoresistance (AMR) position sensor solutions enables robust and accurate position sensing for encoder applications. Position feedback is used for direct position control or for inferring rotational speed and implementing machine speed control in servo drives. Magnetic sensing provides a lower cost solution compared to optical encoders and a more robust solution in industrial applications that are subject to dust and vibration.
Intelligent motion applications are typically deployed in harsh industrial environments where high ambient temperature operation is required, along
10 February 2022 | Automation
with immunity to conducted noise and high voltage transients. In some decentralised applications, drives are located closer to the motor in smaller enclosures and in others the drive is integrated with the motor. Machine health uses vibration and shock sensors to enable real-time condition monitoring of an asset’s health to eliminate unplanned downtime, extending the asset’s useable lifetime while reducing maintenance costs. By integrating machine health into motion applications, new revenue streams can be generated.
Intelligent motion control solutions Analog Devices technologies and system- level solutions for intelligent motion applications are enabling higher levels of performance while reducing energy consumption and downtime. Figure 3 outlines a typical motor drive signal chain that comprises six key blocks. Each block outlines an ADI solution.
Power electronics Power electronics provide the power conversion in a motor drive system. For high voltage systems (> 100V), an isolated gate driver is used to drive the power semiconductors. ADuM4122 is a single-gate isolated gate driver with 3A short circuit (< 3Ω). It supports functional or reinforced isolation up to ~800V DC bus with slew rate control for EMI/ power loss optimisation. It also supports high common-mode transient immunity (CMTI) and low propagation delay for use with SiC and GaN power semiconductors. ADuM160N multichannel digital isolators can be used to isolate PWM signals for use with integrated power modules (IPM) that contain the gate driver and the power semiconductor. The ADuM6028 isolated power device can be used in conjunction with digital isolators, isolated transceivers and isolated data converters to provide a very small 8-lead solution that is fully safety certified and ready to use. For low voltage systems (< 100V), the
LTC7060, a 100V half-bridge driver with floating grounds and programmable dead time, or the LTC7000, a 150V protected high-side NMOS static switch driver with PassThru technology and adaptive shoot-through protection can be used to drive low-voltage semiconductors. LTC7000 also supports programmable dead time for efficiency optimisation, enhanced current control and slew rate control for EMI reduction.
Current sense For isolated current sense measurement, the ADuM7701 is a high-performance, second-order, sigma-delta (Σ-Δ) modulator that converts an analogue input signal into a high-speed, single-bit data stream with on-chip digital isolation based on Analog Devices iCoupler technology. ADuM7703’s low off set drift (0.6μV/°C max) reduces torque ripple and is a compact 8-lead package with integrated LDO to simplify power supply design and reduce board area. Its 150V/ns min CMTI rating enables use with GaN and SiC power electronics. AD8410 high voltage, current sense
amplifi ers provide high gain (20V/V, 50V/V, 100 V/V) and low off set drift (~1μV/°C) with high bandwidth (2MHz) for optimum current control. AD8410 also includes bidirectional current measurement input up to 100V common- mode input. The LTC6102 precision zero-drift current sense amplifi er ensures accuracy across a wide range of operating conditions and can be powered from high- side voltages up to 100V in shunt-based current-sensing applications.
Position sensing
Position feedback is used for direct position control or for inferring rotational speed and implementing machine speed control. ADA4570 and ADA4571 integrated AMR angle sensors with integrated signal conditioners enable higher absolute accuracy position sensing for motor drive and servo applications (< 0.1° error, < 0.5° over life/temperature). They are robust in magnetically harsh environments, support wide air gap tolerances without degradation of angular error (unlike Hall/GMR/TMR), and simplify system design considerations. The ADA4570 and ADA4571 are not aff ected by dust or dirt when compared with optical sensors in industrial applications, and they have very low latency compared to digital output solutions on the market with built-in calibration engines. ADA4571 produces two single-ended analogue outputs (sine and cosine) that indicate the angular position of the surrounding magnetic fi eld, while the ADA4570 produces two diff erential analogue output pairs. A dual version of the ADA4571 (ADA4571-2) is also available where full redundancy is needed in safety-critical applications. The AD7380 is a 4 MSPS dual simultaneous sampling, 16-bit SAR ADC that provides precision, throughput and
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