Miller Plateau in High-Frequency MOSFETs: Principles, Impacts, and Heketa’s Solutions

In the design of high-frequency switching circuits, many engineers encounter a common issue: even when a sufficient voltage is applied to the MOSFET gate, the MOSFET takes a delay to fully turn on, and the gate voltage may even stagnate. This problem is closely related to the Miller plateau, a characteristic phenomenon of MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors). As a critical stage during the MOSFET turn-on process, the Miller plateau directly affects switching speed and circuit efficiency. Combining practical application scenarios, we will elaborate on the principle and impacts of the Miller plateau, as well as Heketa’s device-based solutions to address this challenge.

The Principle of the Miller Plateau

The Miller plateau refers to the stage where the gate voltage of a MOSFET stagnates during its turn-on process. Its core cause lies in the charge coupling effect of the parasitic gate-drain capacitance (Cgd). Taking a common N-channel MOSFET as an example: assume the MOSFET’s drain is connected to a 5V power supply, the source is grounded, and the gate is controlled by 0V and 3.3V signals.

• When 0V is applied to the gate: The gate-source voltage (Vgs) equals 0, so the MOSFET is in the off state. At this point, the voltage across the gate-source capacitance (Cgs) is 0, and the voltage across the gate-drain capacitance (Cgd) is -5V.
• When the gate signal switches to 3.3V: The drive current starts charging both Cgs and Cgd. The voltage across Cgs rises, while the voltage across Cgd gradually changes from -5V to 0V.

Once Vgs exceeds the threshold voltage (Vth), the MOSFET begins to turn on, and the drain voltage (Vds) drops rapidly. At this moment, the drain side of Cgd discharges to the ground through the now-conducting MOSFET. To balance the voltage change across Cgd, the gate side needs to absorb a large amount of positive charge. As a result, the drive current is “occupied” by Cgd and can no longer continue charging Cgs, causing Vgs to stagnate at a fixed value—this forms the “Miller plateau.” If Cgd is excessively large, it may even draw charge from Cgs, leading to a “dip” in Vgs and a further extension of the switching time.

Practical Impacts of the Miller Plateau

The Miller plateau is not just a theoretical issue; it acts as an “invisible loss source” that directly degrades circuit performance:

1. Increased Switching Loss: The Miller plateau extends the MOSFET’s turn-on time, expanding the overlap region between Vds and drain current (Id). Current rises before Vds fully drops, and this overlap loss can account for over 30% of the total loss. For instance, in a 65W fast-charging circuit, the Miller effect may reduce efficiency from 92% to 88%.
2. Limited High-Frequency Performance: In MHz-level switching circuits (e.g., mobile phone fast chargers, LED drivers), the Miller plateau restricts the MOSFET’s switching speed, preventing the circuit from reaching the designed frequency. For example, a target switching frequency of 1 MHz may only achieve 500 kHz in practice, undermining the goal of power supply miniaturization.
3. Increased Burden on Drive Circuits: To “overcome” the Miller plateau, the drive circuit must supply higher current. Insufficient drive capability can cause Vgs to remain stuck in the plateau phase permanently, leaving the MOSFET unable to fully turn on and leading to circuit failure.

Key to Solving the Miller Effect

The core logic for addressing the Miller effect is to reduce the charge absorption capacity of Cgd and enhance the drive current. Through device optimization and drive solution combinations, Heketa provides engineers with practical approaches:

1. Select MOSFETs with Low Gate-Drain Capacitance (Cgd): Minimize Charge Competition at the Source

Heketa’s HKTD series MOSFETs adopt super-junction technology and trench structures, reducing Cgd to below 50 pF—directly minimizing the “charge competition” between the Miller capacitance (Cgd) and the gate. Take the HKTD100N03 (30V/100A) as an example: its Cgd is only 40 pF, shortening the Miller plateau duration by 20% and reducing switching loss by 15% compared to similar products. It is well-suited for high-frequency, high-current scenarios such as electric vehicle battery management systems (BMS) and mobile phone fast chargers.

2. Use High-Current Drive ICs: Rapidly Compensate for Charge Gaps

Even with optimized low Cgd, sufficient drive current is still required to “pass through” the Miller plateau. Heketa’s HKD series totem-pole drive ICs can deliver a peak current of over 2A, quickly supplementing the charge required by Cgd. When paired with HKTD series MOSFETs, the drive current can fill the Cgd charge gap within 1 μs, allowing Vgs to rapidly rise back to the on-state voltage and completely resolving the “gate voltage stagnation” issue.

3. Emergency Measure: Add a Small Capacitor Between Gate and Source

If device replacement is temporarily unfeasible, a small capacitor (approximately 100 pF) can be connected in parallel between the gate and source. This increases the capacitance of Cgs, making the drive current more “resistant to charge theft” and mitigating the impact of the Miller plateau. However, this is only a temporary solution; long-term resolution still relies on low-Cgd devices and high-performance drive circuits.

Conclusion

The Miller plateau is a common issue in high-frequency MOSFET applications. However, it can be effectively mitigated by understanding its principle and selecting devices with low gate-drain capacitance and robust driving solutions. With years of technical expertise and certifications under the ISO9001 and IATF16949 quality management systems, Heketa provides engineers with reliable devices and technical support. If you encounter problems related to the Miller effect during your design process or wish to learn about the specific parameters of Heketa's HKTD series MOSFETs, please feel free to contact us. Heketa's technical team will respond promptly to address your queries and help your high-frequency circuits achieve efficient and stable operation.

Company Introduction

Founded in 1992, Heketa is a high-tech and "specialized, refined, characteristic, and innovative" enterprise focusing on electronic components, integrating R&D, design, production, and sales. It specializes in providing cost-effective component supply and customization services to meet the R&D needs of enterprises.

• Product Supply Categories: It fully covers discrete devices and passive components such as chip resistors, mainly including MOSFETs, TVS (Transient Voltage Suppressors), Schottky diodes, Zener diodes, fast recovery diodes, bridge rectifiers, diodes, transistors, resistors, and capacitors.
• Two Intelligent Manufacturing Centers: The manufacturing centers in South China and Southwest China (Huizhou: 75,000 m² + Nanchong: 35,000 m²) are equipped with more than 3,000 sets of advanced equipment and testing instruments. In 2024, 3 new semiconductor material subsidiaries were added to control production capacity and delivery efficiency from the source.
• Packaging and Testing OEM Services: It supports sample customization and small-batch trial production. Combined with over 100 patented technologies and the ISO9001 and IATF16949 certification systems, it ensures that "quality first" runs through every link from R&D to delivery.

Adhering to the core values of "customer-oriented and innovation-driven", Heketa consistently provides stable and reliable components for enterprises.

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