Power MOSFETs Suppress Noise in Motor

Power MOSFETs Suppress Noise in Motor-Control Circuits
Vishay Intertechnology introduced a new series of 40-V n-channel power MOSFETs optimized for the noisy environments of motor-control circuits.
The new devices — the SIR5402DP, SIR5404DP, SIR5406DP, and SIR5408DP — are all specifically designed to reduce the risk of unintended switching induced by the gate while limiting switching losses caused by gate noise. Vishay said it addressed the first problem by increasing the minimum gate-source threshold voltage to more than 2.5 V and confronted the second by reducing the QGD/QGS ratios to less than 1.0.
The higher gate-source threshold voltage helps prevent unintended turn-on of the MOSFET in motor-drive circuits, where fast switching speeds can lead to high dv/dt rates. That, in turn, can cause significant LC oscillations between the parasitic inductance of the PCB traces and parasitic capacitance in the MOSFET package. This switching noise may increase the gate voltage enough that it turns on the power transistor, impacting the system’s performance and potentially damaging the power stage in the motor driver.
At the same time, the improved gate-charge ratio further reduces gate-induced voltage fluctuations and the impact of gate noise, improving switching stability and reliability along with overall circuit robustness, said Vishay.
These noise-rejection characteristics are suitable for synchronous rectification and DC-DC conversion stages in brushless DC (BLDC) motor drives, cordless power tools, drones, and other systems requiring reliable operation in noisy conditions. By mitigating the effects of gate noise, the devices also deliver higher performance by reducing the risk of unwanted switching and the power losses that come with it.
Housed in a compact PowerPAK SO-8 package measuring 6.15 × 5.15 mm, they undergo rigorous testing to verify device robustness.
The devices strike a balance between conduction losses and switching performance with typical on-resistance (RDS(on)) values ranging from 0.9 m to 2.5 mΩ at a gate drive of 10 V and gate charge (QG) values from 32.6 to 82 nC.
About the Author
James Morra
Senior Editor
James Morra is the senior editor for Electronic Design, covering the semiconductor industry and new technology trends, with a focus on power electronics and power management. He also reports on the business behind electrical engineering, including the electronics supply chain. He joined Electronic Design in 2015 and is based in Chicago, Illinois.

Facts Only

* Vishay Intertechnology introduced four 40-V n-channel power MOSFETs: SIR5402DP, SIR5404DP, SIR5406DP, and SIR5408DP.
* The devices are optimized for noisy motor-control circuits.
* The design addresses unintended switching induced by the gate and limits switching losses from gate noise.
* The first problem is addressed by increasing the minimum gate-source threshold voltage to more than 2.5 V.
* The second problem is addressed by reducing the QGD/QGS ratios to less than 1.0.
* Higher gate-source threshold voltage prevents unintended turn-on in motor-drive circuits with fast switching speeds.
* Fast switching causes high $dv/dt$ rates, leading to LC oscillations between parasitic PCB inductance and MOSFET package capacitance.
* Switching noise can increase the gate voltage sufficiently to turn on the power transistor.
* Improved gate charge ratio reduces gate-induced voltage fluctuations and gate noise impact.
* The devices are suitable for synchronous rectification and DC-DC conversion in BLDC motor drives, cordless power tools, drones, and other systems in noisy conditions.
* Typical $R{DS(on)}$ values range from 0.9 m$\Omega$ to 2.5 m$\Omega$ at a 10 V gate drive.
* Typical gate charge ($QG$) values range from 32.6 to 82 nC.
* The devices are housed in a PowerPAK SO-8 package measuring 6.15 × 5.15 mm.

Executive Summary

Vishay Intertechnology introduced a new series of 40-V n-channel power MOSFETs, specifically the SIR5402DP, SIR5404DP, SIR5406DP, and SIR5408DP, optimized for noisy motor-control circuits. These devices are designed to mitigate unintended switching caused by gate activity while simultaneously limiting switching losses resulting from gate noise. This is achieved by increasing the minimum gate-source threshold voltage above 2.5 V and reducing the QGD/QGS ratios to below 1.0. The increased threshold voltage prevents unintended turn-on in motor-drive circuits that experience fast switching, which otherwise causes high $dv/dt$ rates leading to LC oscillations between parasitic PCB inductance and MOSFET package capacitance. Furthermore, the improved gate charge ratio reduces gate-induced voltage fluctuations, enhancing switching stability and reliability. These noise-rejection features are beneficial for synchronous rectification and DC-DC conversion stages in applications such as BLDC motor drives, power tools, and drones operating in noisy environments. The devices offer a balance between conduction losses and switching performance, exhibiting typical on-resistance ($R{DS(on)}$) values from 0.9 m$\Omega$ to 2.5 m$\Omega$ at a 10 V gate drive, with gate charge ($QG$) values ranging from 32.6 to 82 nC.

Full Take

The narrative positions hardware design not merely as an optimization of electrical parameters, but as a necessary battle against physical noise and system instability arising from high-speed operation. The core implication is that the performance limitations in power electronics systems are frequently dictated by parasitic effects (inductance/capacitance) amplified by aggressive switching characteristics. The solution proposed—adjusting intrinsic MOSFET properties ($V{GS(th)}$ and $QGD/QGS$)—shifts the locus of control from external circuit design alone to the semiconductor device itself, embedding noise resilience directly into the transistor architecture. This moves the discussion beyond simple loss minimization toward systemic reliability engineering in dynamic environments like drone operation or motor control.
The focus on gate charge ratio and threshold voltage suggests a deeper pattern: stability is achieved by controlling the energy dynamics at the switching interface. If one assumes that external system design (PCB layout, driver circuitry) cannot be perfectly controlled—which is often true in complex systems—then the component itself must possess inherent resistance to those environmental disturbances. This anticipates a broader trend where electronic components are increasingly expected to manage complex physical interactions autonomously rather than relying solely on perfect external control signals. The skepticism should focus on whether this intrinsic tuning adequately accounts for all potential noise sources outside the explicit gate-switching mechanism, and whether the stated $R{DS(on)}$ and $QG$ trade-offs perfectly reflect real-world operational robustness across varied thermal regimes.
Bridge Questions: If system designers cannot eliminate parasitic inductance entirely, what further constraints must be placed on gate noise to guarantee functional safety in highly variable motor applications? How does this approach change the traditional division of responsibility between the control circuit designer and the semiconductor manufacturer regarding noise mitigation in power systems? Does optimizing for gate noise inherently introduce new, unstated trade-offs related to thermal management or long-term reliability that require further scrutiny?