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Qorvo SiC FETS: explaining the technical advantages of the Cascode configuration

Updated: Aug 4

Qorvo SiC MOSFET Applications

The Rise of Wide Band Gap Devices

In the realm of high-voltage and high-power applications, Wide Band Gap Devices, particularly Silicon Carbide (SiC) Field Effect Transistors (FETs), are gaining traction. Their inherent capability to achieve higher switching frequencies translates to superior efficiency compared to traditional Silicon FETs.

SiC MOSFETs vs. Silicon MOSFETs

SiC MOSFETs offer superior performance in many aspects, especially for applications that demand high power, high frequency, and high efficiency. However, they falter when it comes to the MOS channel resistance. This resistance can significantly inflate the die size, a challenge not present in Silicon MOSFETs. However, the industry's solution to this has often been the "normal" SiC MOSFETs, which carry this inherent disadvantage.

JFETs: The Game Changer

Image of circuit diagram of Cascode configuration on a SiC JFET

Junction Field-Effect Transistors (JFETs) emerge as a solution to the channel resistance conundrum. Absent of this resistance, JFETs promise a reduced on-resistance for an equivalent die size. However, they come with a caveat: they are "normally-on" devices. To counter this, engineers have turned to a cascode configuration, a combination of a SiC JFET and Si MOSFET. This hybrid offers a "normally-off" device, encapsulating the benefits of a SiC JFET. Qorvo, leading the charge, has seamlessly integrated this SiC JFET + Si MOSFET cascode into a singular package.

Technical Advantages of Cascode Configurations with SiC FETs

The cascode configuration, especially when applied to Silicon Carbide (SiC) Field-Effect Transistors (FETs), offers several technical advantages that make it particularly attractive for high-frequency and high-power applications.

  1. Voltage Handling: The cascode configuration combines a low-voltage MOSFET with a high-voltage SiC JFET. This allows the device to handle higher voltages than a standalone MOSFET, making it suitable for high-voltage applications.

  2. Switching Speed: SiC FETs inherently have fast switching speeds due to the material properties of SiC. When used in a cascode configuration, the switching losses are further minimized, which is beneficial for high-frequency applications.

  3. Thermal Performance: SiC has excellent thermal properties, allowing the device to operate at higher temperatures than traditional silicon devices. The cascode configuration further improves thermal performance by distributing the heat between the MOSFET and the JFET.

  4. Drive Simplicity: Despite the complexity of the cascode configuration, it can be driven like a traditional MOSFET. This simplifies the gate drive requirements and makes it easier to integrate into existing designs.

  5. Reduced Miller Effect: The cascode configuration reduces the Miller capacitance, which is the capacitance between the gate and the drain of a FET. This reduction minimizes the Miller effect, which can cause unwanted feedback and oscillations in high-frequency circuits.

  6. Improved Reliability: The cascode configuration offers inherent protection to the SiC JFET from voltage spikes and transients. This enhances the overall reliability of the device in challenging operating conditions.

Transitioning to Qorvo SiC FETs

Transitioning to Qorvo’s SiC FETs requires a nuanced approach. Their rapid switching capabilities and superior body diode characteristics mean the operating di/dts value can be exceptionally high. To manage these high di/dts, it's often recommended to integrate an RC snubber. This addition can help in:

  • Mitigating voltage overshoots

  • Curbing gate oscillations

  • Enhancing EMI

For a comprehensive understanding, Qorvo's application notes and user guides are invaluable resources.

Qorvo’s application note and user guide show this in more detail:

Qorvo's SiC FET Portfolio Overview

Qorvo's SiC FETs come with a diverse range of parameters:

  • 650V: RDS,ON ranging from 6.7mOhm to 85mOhm, with a maximum ID of up to 85A.

  • 750V: RDS,ON between 5.4mOhm and 58mOhm, with a maximum ID of up to 120A.

  • 1200V: RDS,ON from 9mOhm to 410mOhm, with a maximum ID of up to 120A.

  • 1700V: RDS,ON at 410mOhm, with a maximum ID of up to 7.6A.

These are available in packages such as D2PAK-3L, D2PAK-7L, TO-220-3L, and TO247 with 3 or 4 leads. The 750V lineup also boasts a TOLL package option.

For more information, samples and pricing, please contact your local Ineltek agent.

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