Unlocking Superior Motion Control with an Isolated ADC—Part 1: High‑Frequency PWM Control

• Share on X
• Share on LinkedIn

August 13, 2026

Blog

Understanding Power and Control Electronics for Motor Drives

Industrial automation is entering a new era, driven by the demand for faster, more precise, and highly reliable motion control systems. As manufacturers transition from traditional insulated-gate bipolar transistor (IGBT)-based motor drives to advanced silicon carbide (SiC) and gallium nitride (GaN) technologies, the requirements for speed, accuracy, and system robustness have never been greater.1,2

Meeting these challenges calls for innovation, not only in power electronics but also in the way current is measured and controlled within motor-drive architectures. This three-part article series uses the servo drive architecture illustrated in Figure 1 as a test vehicle to understand trade-offs in power conversion, motor current measurement, and control.

• Part 1 of this article series will introduce Analog Devices’ 230VAC servo drive, including key elements of power supply design, power conversion architecture (variable frequency drive) using SiC, and closed-loop feedback using isolated ADCs.
• Part 2 of this article series will look more closely at the ADuM7811’s industry-leading signal-to-noise ratio (SNR) and benefits for motor-drive systems, including better precision and smoother motion/less vibration.
• Part 3 of this article series will focus on the device’s ultra-low latency, enabling faster control loops and enhancing torque responsiveness for applications like computer numerical control (CNC) machines.

Figure 1. Servo drive architecture diagram.

Motor Drives Using SiC

IGBTs have been the standard for a long time in industrial motor drives and have the largest install base. They are limited in switching frequency (2kHz to 16kHz) due to high turn-off losses. This means motors hear audible pulse-width modulation (PWM) noise unless high-pole motors are used. IGBTs are lower cost per amp compared to SiC or GaN. Market reports predict moderate growth for IGBTs, in single-digit percentages.1 SiC MOSFETs are the fastest-growing power switch technology.2 Using higher PWM with SiC (10kHz to 100kHz) allows improved current control bandwidth and reduced torque ripple. SiC needs careful gate-drive and electromagnetic interference (EMI) design and has higher cost per kW than IGBT, but cost is falling fast.

SiC technologies demand a holistic upgrade of the motion control system, including faster and more precise current measurement, advanced gate drive and EMI mitigation, and robust safety and isolation features. These requirements are essential to fully leverage the performance advantages of wide-bandgap semiconductors in modern industrial and automation applications.

Moving from IGBT to SiC/GaN means faster PWM frequencies, faster motion control loops, and faster (low-latency) current-isolated measurements, as illustrated in Figure 2.

Figure 2. Isolated ADC MCLK, total delay (latency), and PWM switching frequency.

Closed-Loop Feedback Using the ADuM7811

Latency is defined as the total delay of the ADC + sinc3 filter (also known as settling time). The ADuM7811 has market-leading latency, capable of as low as 5µs for oversampling ratio (OSR) = 64, MCLK = 50MHz, as shown in Figure 3. ADI has tested lower isolated ADC latency and system benefits. This will be presented in Part 3 of this series.

Figure 3. Isolated ADC latency as low as 5µs for the ADuM7811 and ADuM7703.

Figures 4 and 5 show some field-oriented control (FOC) loop timing examples with sigma-delta current measurement. These show that if current sampling timing is reduced, for example from 41µs to 16µs, then overall timing for the current control loop can be reduced, and higher PWM frequencies can be achieved. These examples show 16.5kHz increasing to 28.5kHz. These examples are conservative in nature (sigma-delta measurement may be optimized3 to cover 100% of PWM period and perform control in parallel as shown in Figure 6).

Even though the FOC current loop runs, for example, every 30µs, the torque response is slower—typically around 1ms to 3ms—because the motor’s mechanical system (rotor and load) has inertia and can’t react instantly. Parts 2 and 3 of this article series will present this topic in more detail.

Isolated Gate Driver and SiC

The adoption of SiC MOSFETs over IGBTs is beneficial in motor-drive control systems, unlocking higher PWM frequencies that lead to a higher current control bandwidth and lower torque ripple. This evolution introduces new requirements for gate drivers too, which must be carefully selected to meet the challenges associated with SiC operation. Next, the basic characteristics an isolated SiC gate driver should have in a motor-drive system will be discussed, and the ADuM4221 will be introduced; the new dual-channel isolated gate driver specifically designed to meet these emerging demands.

Gate-Driver Supply

Modern SiC MOSFETs typically require a bipolar gate-source voltage, with a positive level of approximately 15V to 18V for turn-on and a negative level between –3V and –4V for turn-off, which define, in turn, the electrical requirements for the driver supply stage.

Propagation Delay and Jitter

With frequencies in the range of 100kHz, SiC systems require more precise timing than ever to balance loss and shoot-through risk. Optocouplers often cannot guarantee this balance because higher delay, jitter, and aging/temperature drift degrade PWM accuracy over time. Digital isolator gate drivers like the ADuM4221 maintain timing integrity with propagation delays of less than 44ns and jitter of less than 10ns, reducing skew and drift for predictable switching, providing a safer and more reliable operation at higher frequencies.

Common-Mode Transient Immunity (CMTI)

Shifts between primary and secondary grounds, known as common-mode transients, affect any isolated gate driver in a half-bridge configuration and can interfere with data transfer across the isolation barrier. If the isolator is unable to handle these events, the system may experience unintended turn-on or turn-off, corrupted status signals, or loss of control communication. The ADuM4221 (as shown in Figure 7), with a CMTI greater than 150kV/ns, can overcome SiC application requirements, where dv/dt values often reach extreme levels and a CMTI rating above 100kV/µs is generally required to guarantee robust and error-free operation.

Figure 4. FOC current control loop, >16.5kHz PWM.

Figure 5. FOC current control loop, >28.5kHz PWM.

Figure 6. FOC current control loop, >38kHz PWM optimized for sigma-delta measurement.

Figure 7. ADuM4221 common-mode transient immunity.

Isolation Requirements

Isolation is essential in motor-drive systems to protect low-voltage control electronics from high-voltage hazards and to meet safety and regulatory requirements, but it is also essential to provide a correct driving voltage to the high-side switch. Figures 8 and 9 illustrate a typical isolated architecture. A gate driver with a robust isolation barrier is critical for motor-drive system reliability, protecting low-voltage controls, providing a correct driving voltage, and is part of safety and regulatory requirements (for example, IEC 61800-5-1).

Figure 8. Isolated gate driver and SiC power inverter.

Figure 9. Isolated power, gate driver, and current sensing.

Power Supply Design

Power supply design is an especially important consideration when it comes to isolated systems—but it rarely gets the spotlight until noise, heat, or board space become an issue. Designing with an isolated power supply is a way to control noise and to prevent the creation of ground loops. With the inherent complexity of designing a power supply for industrial electronics, choosing intelligent and flexible isolation components can simplify the process and prevent common errors, allowing design engineers to focus their efforts on the wider system.

Take, for example, the LT8316 (as shown in Figure 10), which is a high-voltage, no-opto isolated flyback controller capable of operating from 16V to 560V, making it suitable for everything from industrial DC buses to rectified mains. It samples the output voltage through the transformer’s auxiliary winding, eliminating the need for an optocoupler. The wide input voltage and small form factor can greatly reduce the complexity overhead on the designer. Noise in the system is reduced both through the replacement of the optocoupler (which is noise sensitive) and through other smart features of the LT8316, such as low-ripple burst mode and quasi-resonant boundary mode operation.

Figure 10. Main 230VAC power supply design detail.

One further consideration is that many electronic circuits will have multiple voltage rail requirements. This is especially true for complex systems such as motor drives, and isolation requirements can further complicate this issue.

The LT8686S, as illustrated in Figure 11, is a 4-channel synchronous step-down regulator that delivers high output current in an exceptionally compact footprint. Its Silent Switcher® architecture minimizes EMI and switching noise, making it ideal for noise sensitive industrial environments. With integrated power MOSFETs and straightforward compensation, it’s easy to integrate into system design and can reduce external component count and layout complexity. A thermal shutdown mode is incorporated, which protects both the device and the surrounding system from damage caused by excess temperature during operation. Additionally, the LT8686S supports high switching frequencies, enabling very small inductors and capacitors, resulting in outstanding current-to-PCB area ratio, perfect for dense, space-constrained boards.

Figure 11. The LT8686S power supply design detail.

Conclusion

This article introduces next-generation industrial motion systems, especially those using SiC and GaN, that require a holistic redesign of sensing, control, and power-delivery electronics. The ADuM7811 isolated ADC emerges as a central component in this evolution thanks to its ultra-low latency, high SNR, and robust noise immunity, enabling faster control loops and smoother, more precise motor operation.

The article also emphasizes that achieving full benefits of wide-bandgap power devices requires complementary improvements in isolated gate drivers, high-CMTI interfaces, and low-noise power supplies such as the LT8686S. Together, these technologies form the backbone of modern servo drives capable of higher PWM frequencies, improved torque response, and greater overall efficiency.

Part 1 lays the groundwork for the next articles, which will explore the ADuM7811 SNR advantages and its impact on precision motor control.

References

1“Insulated Gate Bipolar Transistors Market Size & Share Analysis—Growth Trends and Forecast (2026–2031).” Mordor Intelligence.

2“Silicon Carbide Power Semiconductor Market Size & Share Analysis—Growth Trends and Forecast (2026–2031).” Mordor Intelligence.

3Jens Sorensen, Dara O’Sullivan, and Shane O’Meara. “Optimized Sigma-Delta Modulated Current Measurement for Motor Control.” Analog Dialogue, Vol. 53, October 2019.