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πŸ“– MOSFET & GaN FET πŸ“•

May 16, 202435 min read

Chapter 1: Understanding power MOSFET data sheet parameters

This chapter provides a comprehensive guide to understanding the parameters in a power MOSFET datasheet. It aims to assist engineers in selecting the most suitable device for their specific applications. The chapter emphasizes the importance of paying attention to the conditions under which parameters are listed, as these can vary among suppliers and affect the interpretation of device capabilities.

Key Sections in Datasheets

Nexperia power MOSFET datasheets typically include the following sections:

  1. General Description: Provides an overview of the MOSFET technology, package type, and relevant qualifications (e.g., AEC-Q101 for automotive applications).
  2. Features and Benefits: Highlights the key features of the MOSFET and the advantages they offer.
  3. Applications: Lists the specific applications for which the MOSFET is well-suited.
  4. Quick Reference Data: Presents a concise summary of essential parameters and their values under specific conditions.
  5. Pinning Information: Details the internal connections and layout of the device.
  6. Ordering Information: Provides instructions on how to order the device, including package versions and common package names.
  7. Limiting Values: Specifies the maximum operating conditions allowed for the MOSFET, such as voltage, current, and power dissipation limits.
  8. Thermal Characteristics: Describes the thermal behavior of the device, including thermal resistance and impedance.
  9. Electrical Characteristics: Details the static and dynamic electrical parameters of the MOSFET.
  10. Package Outline: Provides a drawing of the physical dimensions and layout of the MOSFET package.

Quick Reference Data

The quick reference data table offers a snapshot of the MOSFET’s key parameters, including:

  • VDS (Drain-Source Voltage): The maximum voltage the device can block in the off-state.
  • ID (Drain Current): The maximum continuous current the device can handle under specified conditions.
  • Ptot (Total Power Dissipation): The maximum continuous power the device can dissipate.
  • RDS(on) (Drain-Source On-State Resistance): The resistance of the device when it is fully turned on.
  • QGD (Gate-Drain Charge): A switching parameter related to switching losses.
  • Qr (Recovered Charge): The charge recovered from the body diode during switching.

Limiting Values

The limiting values table defines the safe operating limits of the MOSFET. Exceeding these limits can lead to device failure or reduced lifespan. Key parameters in this table include:

  • VDS (Drain-Source Voltage): The maximum allowable voltage between the drain and source terminals.
  • VGS (Gate-Source Voltage): The maximum allowable voltage between the gate and source terminals.
  • ID (Drain Current): The maximum allowable continuous drain current.
  • IDM (Peak Drain Current): The maximum allowable pulsed drain current.
  • Ptot (Total Power Dissipation): The maximum allowable continuous power dissipation.
  • Tj (Junction Temperature): The maximum allowable operating temperature of the device.
  • EAS(AL)S (Non-Repetitive Drain-Source Avalanche Energy): The maximum allowable single overvoltage energy pulse.

Derating Curves

Derating curves illustrate how the MOSFET’s limiting values change with temperature. These curves are crucial for understanding the device’s performance under varying thermal conditions.

Thermal Characteristics

The thermal characteristics section provides information about the MOSFET’s thermal impedance as a function of pulse duration and duty cycle. This data is essential for determining the device’s temperature under different operating conditions.

Electrical Characteristics

The electrical characteristics section details the static and dynamic electrical parameters of the MOSFET.

Static Characteristics

  • VBR(DSS) (Drain-Source Breakdown Voltage): The minimum voltage the device can block in the off-state across its entire temperature range.
  • VGS(th) (Gate-Source Threshold Voltage): The gate-source voltage required to initiate conduction.
  • IDSS (Drain Leakage Current): The maximum leakage current in the off-state.
  • IGSS (Gate Leakage Current): The maximum leakage current through the gate.
  • RDS(on) (Drain-Source On-State Resistance): The resistance of the device when fully turned on.
  • RG (Gate Resistance): The internal resistance of the gate.

Dynamic Characteristics

  • QG (Total Gate Charge): The total charge required to switch the MOSFET.
  • QGS (Gate-Source Charge): The portion of the gate charge associated with charging the gate-source capacitance.
  • QGD (Gate-Drain Charge): The portion of the gate charge associated with charging the gate-drain (Miller) capacitance.
  • Ciss (Input Capacitance): The capacitance between the gate and source/drain terminals.
  • Coss (Output Capacitance): The capacitance between the drain and source/gate terminals.
  • Crss (Reverse Transfer Capacitance): The capacitance between the drain and gate terminals.
  • td(on) (Turn-On Delay Time): The time delay between the gate voltage reaching a specified threshold and the drain current reaching a specified value.
  • tr (Rise Time): The time it takes for the drain current to rise from a specified low value to a specified high value.
  • td(off) (Turn-Off Delay Time): The time delay between the gate voltage falling below a specified threshold and the drain current falling below a specified value.
  • tf (Fall Time): The time it takes for the drain current to fall from a specified high value to a specified low value.

Safe Operating Area (SOA)

The Safe Operating Area (SOA) curves are crucial for understanding the MOSFET’s safe operating limits in terms of voltage, current, and time. These curves help prevent device failure due to excessive power dissipation.

Thermal Runaway in Linear Mode

The chapter also discusses the concept of thermal runaway in linear mode operation. This phenomenon occurs when a MOSFET operates in the linear region with low current density and high drain-source voltage, potentially leading to a positive feedback loop and device failure.

Conclusion

Understanding the parameters in a power MOSFET datasheet is essential for selecting the right device and ensuring its reliable operation in various applications. By carefully considering the limiting values, thermal characteristics, electrical characteristics, and safe operating area, engineers can make informed decisions and optimize their designs for performance and longevity.

Chapter 2: Designing in MOSFETs for Safe and Reliable Gate-Drive Operation

This chapter focuses on designing MOSFET gate-drive circuits for safe and reliable operation. It emphasizes the importance of understanding the gate-source threshold voltage (VGS(th)) and the maximum gate-source voltage (VGS-max) for ensuring MOSFET reliability.

Key Points

  1. VGS(th) (Gate-Source Threshold Voltage):

    • Represents the voltage at which the MOSFET begins to turn on.
    • Varies with temperature, having a negative temperature coefficient (NTC).
    • Important for determining the correct gate driver voltage to fully turn the MOSFET on and off.

  2. VGS-max (Maximum Gate-Source Voltage):

    • The absolute maximum gate-source voltage the MOSFET can safely withstand.
    • Exceeding this rating can lead to gate oxide breakdown and MOSFET failure.
    • Varies between suppliers and MOSFET types.

  3. Life Testing and Qualification:

    • Automotive MOSFETs undergo rigorous life testing to ensure compliance with AEC-Q101 standards.
    • Nexperia employs additional testing methodologies to achieve sub-ppm (parts per million) defect rates.

  4. Gate Oxide:

    • The insulating layer between the gate and source terminals.
    • Its thickness affects both RDS(on) and VGS-max.
    • Thinner gate oxides are needed for logic-level MOSFETs, resulting in lower VGS-max ratings compared to standard-level MOSFETs.

  5. Alternative Operating Profiles:

    • Real-world operating conditions often differ from the worst-case scenarios used for qualification.
    • Understanding the MOSFET’s mission profile (VGS, temperature, and duration) is crucial for selecting the right device.

  6. Application Assessments:

    • Analyzes common MOSFET topologies (single MOSFETs, half-bridges, three-phase bridges) to understand their impact on VGS.
    • Recommends driving MOSFETs with respect to their source terminals (not ground) for better control and reliability.

  7. Creating a Mission Profile:

    • Involves gathering information about the application’s operating conditions, including on/off times, temperatures, and supply voltages.
    • This profile helps assess the MOSFET’s suitability against Time-Dependent Dielectric Breakdown (TDDB) data.

Conclusion

Designing MOSFET gate-drive circuits requires careful consideration of VGS(th) and VGS-max ratings. Understanding the MOSFET’s mission profile and working with suppliers like Nexperia can help ensure reliable operation and optimal performance in various applications.

Chapter 3: Using Power MOSFETs in Parallel

This chapter explores the concept of paralleling power MOSFETs to increase the current-carrying capability of a switch element. It discusses the challenges and considerations involved in designing parallel MOSFET configurations.

Key Points

  1. Static (DC) Operation:

    • In DC operation, the MOSFET with the lowest RDS(on) initially carries the highest current and dissipates the most power.
    • The positive temperature coefficient (PTC) of RDS(on) helps redistribute current among MOSFETs as they heat up, promoting thermal stability.
    • The maximum junction temperature (Tj) of any MOSFET in the group must not exceed 175Β°C.

  2. MOSFET Mounting:

    • MOSFETs should be mounted symmetrically and close together on a thermally conductive surface to ensure even heat distribution.
    • Thermal resistance from the mounting base to ambient (Rth(j-a)) should be minimized and matched for all MOSFETs in the group.

  3. Power Sharing in Dynamic Operation:

    • In dynamic operation (pulse and PWM circuits), source inductances and resistances affect current sharing during switching transitions.
    • Minimizing and matching these impedances is crucial for optimal performance, especially in high-frequency applications.

  4. Partially Enhanced (Linear Mode) Operation:

    • Requires special attention due to the negative temperature coefficient (NTC) of the gate threshold voltage (VGS(th)).
    • External source resistors can provide negative feedback for stable operation in linear mode.

  5. Gate Drive Considerations:

    • Using low-value gate resistors between the gate driver and each MOSFET helps decouple the gates and ensure similar gate drive signals.
    • Individual gate drivers for each MOSFET are usually unnecessary unless fast switching of a large group of MOSFETs is required.

  6. MOSFET Packaging:

    • Bare die (KGD) MOSFETs offer the highest density and flexibility for parallel configurations.
    • LFPAK (Power SO8) MOSFETs provide a good compromise between performance and ease of manufacturing.

  7. Inductive Energy Dissipation:

    • When driving inductive loads, energy stored in the inductor must be safely dissipated during switching.
    • Avalanching or active clamping techniques can be used to manage this energy.

Conclusion

Paralleling power MOSFETs can be an effective way to increase current capability, but careful design considerations are necessary to ensure proper power sharing, thermal stability, and reliable operation under various operating conditions.

Chapter 5: Using RC Thermal Models

This chapter introduces the concept of using RC (Resistor-Capacitor) thermal models to analyze and predict the thermal behavior of power MOSFETs. These models provide a convenient way to simulate the transient thermal response of MOSFETs under different power dissipation conditions.

Key Points

  1. Thermal Impedance (Zth):

    • Represents the transient thermal response of a device to power pulses.
    • For long-duration pulses (> 1 second), Zth approaches the steady-state thermal resistance (Rth).
    • Zth curves for repetitive pulses with different duty cycles are also provided.

  2. Calculating Junction Temperature Rise:

    • For square power pulses, the temperature rise can be calculated by multiplying the power by the corresponding Zth value.
    • For constant power, the steady-state Rth is used.
    • For complex transient pulses, the convolution integral or superposition methods can be used.

  3. Thermal-Electrical Analogy:

    • Thermal parameters can be represented by electrical equivalents:
      • Temperature difference (K) is analogous to voltage (V).
      • Rate of heat flow (W) is analogous to current (A).
      • Thermal resistance (K/W) is analogous to electrical resistance (Ξ©).
      • Thermal capacitance (J/K) is analogous to electrical capacitance (F).

  4. Foster and Cauer RC Thermal Models:

    • Foster models are one-dimensional RC networks fitted to the Zth curve.
    • Cauer models are equivalent representations of Foster models, with thermal capacitances connected to thermal ground (ambient temperature).
    • Nexperia provides both Foster and Cauer models for many of its automotive power MOSFETs.

  5. Thermal Simulation Examples:

    • Example 1: Demonstrates how to plot a Zth curve from an RC model in a SPICE simulator.
    • Example 2: Shows how to use a PWL (Piecewise Linear) file to input a power profile into the simulation.
    • Example 3: Illustrates how to integrate a MOSFET electrical circuit with a thermal model to simulate junction temperature rise.

Conclusion

RC thermal models offer a valuable tool for analyzing the thermal behavior of power MOSFETs. By understanding the principles behind these models and utilizing simulation tools, engineers can optimize their designs for efficient heat dissipation and ensure the reliable operation of MOSFETs in various applications.

Chapter 6: Designing RC Snubbers

This chapter details the design of RC snubber circuits, which are used to suppress high-frequency oscillations caused by reverse recovery effects in power semiconductor applications.

Key Points

  1. Test Circuit:

    • The chapter uses a half-bridge circuit with two MOSFETs (Q1 and Q2) and an inductor as the test setup.
    • The reverse recovery of Q1 during switching induces oscillations in the drain-source voltage (VDS) of Q2.

  2. Determining Parasitic Elements:

    • The circuit’s parasitic elements, leakage inductance (LLK) and parasitic capacitance (CLK), need to be determined before designing the snubber.
    • A method involving adding an extra capacitor (Cadd) and measuring the change in oscillation frequency is used to calculate CLK and LLK.

  3. Designing the Snubber (Theory):

    • The snubber consists of a resistor (RS) and a capacitor (CS) in series, placed across Q1’s drain-source.
    • The damping factor (ΞΆ) of the RLC circuit (formed by LLK, CLK, and RS) determines the circuit’s response to a step change in voltage.
    • The chapter explains the concept of underdamped, critically damped, and overdamped responses.

  4. Designing the Snubber (Practice):

    • The chapter provides a practical example of designing a snubber for the test circuit.
    • The values of RS and CS are chosen based on the desired damping factor and the calculated values of CLK and LLK.
    • The snubber effectively eliminates the ringing in the VDS waveform.

Conclusion

RC snubbers are essential for suppressing high-frequency oscillations in power semiconductor circuits. By understanding the circuit’s parasitic elements and the desired damping factor, engineers can design effective snubbers to improve circuit performance and reduce EMI.

Chapter 7: Half-Bridge MOSFET Switching and Its Impact on EMC

This chapter delves into the switching behavior of MOSFETs in half-bridge configurations and its impact on electromagnetic compatibility (EMC). It discusses double pulse testing, a technique used to assess switching efficacy, and explores methods to improve switching performance.

Key Points

  1. Double Pulse Testing:

    • A method to analyze the switching behavior of MOSFETs in a half-bridge circuit.
    • Involves switching one MOSFET (Q2) on and off twice while the other MOSFET (Q1) acts as a diode.
    • Allows for the evaluation of switching behavior at specific current and voltage levels.

  2. Measurement System:

    • Emphasizes the importance of using a high-bandwidth current sensor (e.g., coaxial shunt) to capture fast switching transients.
    • Recommends using an oscilloscope with sufficient bandwidth and sampling rate for accurate measurements.

  3. MOSFET Switching Simulation:

    • SPICE simulation is used to model the double pulse test circuit and generate waveforms for analysis.
    • The simulation helps understand the switching behavior and identify potential issues.

  4. MOSFET Turn-Off Waveform:

    • Describes the different phases of the turn-off process, including the Miller plateau and the interaction of parasitic capacitances and inductances.
    • Explains the causes of voltage overshoot and ringing in the waveforms.

  5. MOSFET Turn-On Waveform:

    • Details the turn-on process, including the interaction of parasitic capacitances and inductances.
    • Discusses the concept of reverse recovery and its impact on switching behavior.

  6. Methods to Improve Switching Performance:

    • Suggests techniques to minimize voltage spikes, ringing, and feedback into the gate signal.
    • These techniques include optimizing circuit layout, reducing dI/dt, selecting appropriate bypass capacitors, and adding snubber circuits.

  7. Impact on EMC and Efficiency:

    • Explains how voltage transients and oscillations generated during switching can lead to electromagnetic interference (EMI).
    • Emphasizes the importance of suppressing EMI to comply with EMC standards.

Conclusion

Understanding the switching behavior of MOSFETs in half-bridge configurations is crucial for optimizing circuit performance, efficiency, and EMC compliance. By employing appropriate measurement techniques, simulation tools, and mitigation strategies, engineers can design robust and efficient power electronic systems.

Chapter 8: Failure Signature of Electrical Overstress on Power MOSFETs

This chapter focuses on the failure signatures of power MOSFETs under various electrical overstress (EOS) conditions. It provides a catalog of failure signatures to aid in forensic investigations and improve module design and reliability.

Key Points

  1. Electrical Overstress (EOS):

    • Occurs when voltage, current, or power applied to the MOSFET exceeds its capability.
    • Can be caused by electrical circuit failures or mechanical faults in loads.

  2. Common Fault Conditions:

    • Electrostatic Discharge (ESD)
    • Unclamped Inductive Switching (UIS)
    • Linear Mode Operation
    • Overcurrent

  3. ESD (Human Body Model):

    • Simulates voltage spikes applied to the MOSFET, exceeding the gate oxide’s capability.
    • Failure signature: Typically located in an edge cell of the MOSFET structure.

  4. UIS (Avalanche or Ruggedness):

    • Simulates situations where the MOSFET is switched off with an inductive load, leading to avalanche breakdown.
    • Failure signature: Round burn marks in active MOSFET cells, often near wire bonds/clip bonds.

  5. Linear Mode Operation:

    • Occurs during switching or clamped inductive switching when the MOSFET operates in the linear region.
    • Failure signature: Burn marks located in the center of the die, often adjacent to wire bonds/clip bonds.

  6. Overcurrent:

    • Happens when the MOSFET is turned on with no current limiting element, leading to excessive current flow.
    • Failure signature: Extensive damage starting from where current-carrying connections meet the die, often with melted metallization and fused wires.

Conclusion

Examining the failure signatures of power MOSFETs under EOS conditions can provide valuable insights into the root causes of failures. This information can be used to improve circuit design, enhance MOSFET reliability, and prevent future failures in power electronic applications.

Chapter 9: LFPAK MOSFET Thermal Design Guide

This chapter offers a guide to understanding the power dissipation limits of LFPAK MOSFET packages. It explores the relationship between MOSFET power dissipation and PCB design, focusing on common configurations to maximize power dissipation while maintaining safe operating temperatures.

Key Points

  1. MOSFET Power Dissipation and Thermal Environment:

    • MOSFET power losses consist of switching losses, conduction losses, and avalanche losses.
    • The total power dissipation is the sum of these losses: Ptot​=Psw​+Pcond​+Pav​
    • High ambient temperatures in automotive and industrial applications limit the MOSFET’s power handling capability.
    • Thermal management is crucial to prevent exceeding the maximum operating temperature of both the MOSFET and the PCB material (FR4).

  2. Heat Propagation Phenomena:

    • Heat transfer occurs through conduction, convection, and radiation.
    • Conduction: Heat transfer within a solid medium due to temperature differences.
    • Convection: Heat transfer between a solid and a fluid (gas or liquid) due to fluid motion.
    • Radiation: Heat transfer through electromagnetic radiation (infrared).

  3. Thermal-Electrical Analogy:

    • Thermal systems can be modeled using electrical circuits, with temperature difference analogous to voltage and heat flow analogous to current.
    • Thermal resistance (Rth) is the ratio of temperature difference to heat flow, similar to electrical resistance.
    • Thermal capacitance (Cth) represents heat storage capacity, analogous to electrical capacitance.

  4. MOSFET Steady-State Thermal Characteristics:

    • Rth(j-mb): Thermal resistance from the junction to the mounting base.
    • Rth(j-a): Thermal resistance from the junction to ambient.
    • PCB thermal resistance limits the power dissipation of the MOSFET.
    • The β€œ1-Watt rule” suggests that approximately 1 watt of power can be dissipated in a MOSFET on an FR4 PCB in an 80Β°C ambient environment.

  5. LFPAK56D and LFPAK33:

    • Examines the maximum power dissipation for these packages in a simple PCB configuration with a single copper layer.
    • The junction temperature (Tj) depends on the copper area, but there’s a limit to how much Tj can be reduced by increasing copper area.
    • The maximum power allowed depends on the ambient temperature and copper area.

  6. Usual Configuration (4 Layers + Vias):

    • Analyzes the maximum power dissipation for LFPAK56D and LFPAK33 in a 4-layer PCB configuration with vias for heat dissipation.
    • Similar trends are observed as in the single-layer configuration, with Tj depending on copper area and diminishing returns.
    • The maximum power allowed is higher in this configuration due to improved heat dissipation through vias.

  7. Placement Advice and Package Comparisons:

    • Provides recommendations for MOSFET placement on the PCB to improve heat dissipation.
    • Compares the thermal performance of different LFPAK packages (two LFPAK56 vs. one LFPAK56D, one LFPAK56D vs. two LFPAK33).

  8. LFPAK56 and LFPAK88:

    • Explores the maximum power dissipation for these packages in single-layer and 4-layer PCB configurations.
    • Discusses the impact of splitting the copper layer under the MOSFET into drain and source areas.

  9. Impact of Rth(j-mb) and Rth(mb-a):

    • The thermal resistance from junction to mounting base (Rth(j-mb)) is typically low.
    • The thermal resistance from mounting base to ambient (Rth(mb-a)) is the primary factor limiting heat dissipation.
    • Optimizing PCB layout and thermal vias is crucial for reducing Rth(mb-a).

Conclusion

Efficient thermal design is essential for maximizing the power dissipation capabilities of LFPAK MOSFETs. By understanding the thermal characteristics of these packages and following the design guidelines presented in this chapter, engineers can ensure reliable operation and prevent thermal-related failures in their applications.

Chapter 10: Maximum Continuous Currents in Nexperia LFPAK Power MOSFETs

This chapter delves into the factors that determine the maximum permissible current ratings for LFPAK MOSFETs, particularly in high-power applications like motor drives. It provides insights into the methodology used to establish these ratings and emphasizes the importance of understanding the MOSFET’s capabilities and limitations.

Key Points

  1. LFPAK Advantages:

    • LFPAK packages offer compact size, high power density, and reduced parasitic inductances compared to wire-bonded devices.
    • Copper clip bonding technology enhances current capability and heat dissipation.

  2. Key Parameters and Boundaries:

    • The maximum current rating is influenced by the thermal environment and the conditions affecting MOSFET datasheet parameters.
    • Temperature range: -55Β°C to 175Β°C (junction temperature).
    • Reference temperature (Tmb): 25Β°C (mounting base temperature).
    • Junction temperature limit (Tj): 175Β°C for automotive MOSFETs.

  3. MOSFET Structure and Temperature Properties:

    • Silicon die: Limited to 175Β°C due to reliability requirements.
    • Copper clip: Can handle high temperatures.
    • Solder attach and plastic mold compound: Selected to withstand high temperatures.

  4. Maximum Power and Maximum Current:

    • Maximum power allowance is determined by the thermal impedance (Zth(j-mb)) and thermal resistance (Rth(j-mb)).
    • Maximum continuous drain current (ID) is derived from the maximum power allowance and the MOSFET’s on-state resistance (RDS(on)) at the maximum junction temperature.
    • The theoretical maximum ID is validated through testing, considering package limits, test board limitations, and silicon limits.

  5. Maximum Continuous Source Current (IS):

    • Rated separately from ID, considering the power dissipation through the body diode.
    • The maximum IS is validated through testing.

  6. Practical Application Examples:

    • Discusses the use of MOSFETs in output load drive circuits (motor drives and DC-DC converters), output isolators, and reverse polarity protection.
    • Highlights the importance of considering continuous ID and IS capabilities, as well as SOA performance in specific applications.

Conclusion

Understanding the factors that determine the maximum continuous current ratings of LFPAK MOSFETs is crucial for selecting the appropriate device for high-power applications. By considering the thermal environment, MOSFET structure, and testing methodologies, engineers can ensure reliable and efficient operation in demanding scenarios.

Chapter 11: Thermal Resistance of LFPAK MOSFETs - Simulation, Test, and PCB Layout Optimization

This chapter focuses on the thermal resistance of LFPAK MOSFETs, particularly the junction-to-ambient thermal resistance (), and how it can be minimized through careful PCB layout design.

Key Points

  1. Definition of Thermal Resistance :

    • represents the thermal resistance between the MOSFET’s junction (active area) and the surrounding ambient environment.
    • It quantifies the device’s ability to dissipate heat to its surroundings.
    • is calculated as: ​​ where is the junction temperature, Ta is the ambient temperature, and P is the power dissipated in the MOSFET.

  2. Test Method:

    • The JEDEC standard defines the test method for measuring .
    • The MOSFET is soldered to an FR4 test board and placed in a controlled environment.
    • Heat transfer occurs through conduction, convection, and radiation.

  3. MOSFET Drain-Source Current Path:

    • The current path through an LFPAK MOSFET involves the copper clip attached to the junction.
    • At low currents, the clip acts as a heat sink, but at high currents, it requires cooling by connection to a thermal path.

  4. PCB Layout Optimization:

    • The PCB layout significantly impacts .
    • Trace width calculations using IPC-2221 standards help determine the required trace size to carry the current without excessive heating.
    • Thermal simulations are used to analyze different layout configurations and optimize heat dissipation.

  5. PCB Layout Simulations:

    • Various layouts are tested, including different MOSFET positions within the copper area and varying copper allocation to the source and drain.
    • The impact of trace width on MOSFET and trace temperature is examined.
    • An optimal layout is identified, where the MOSFET is centered on the copper pad with approximately 1/3 allocated to the source pins and the rest to the drain.

Conclusion

Optimizing the PCB layout is crucial for minimizing the thermal resistance of LFPAK MOSFETs. By carefully considering trace widths, copper area allocation, and MOSFET placement, engineers can enhance heat dissipation and ensure reliable operation in high-current applications.

Chapter 12: H-Bridge Motor Controller Design

This chapter presents a practical application of Nexperia MOSFETs and logic ICs in designing an H-bridge motor controller. The design focuses on controlling a brushed DC motor and includes various subsystems for power supply, clock generation, pulse width modulation (PWM), drive circuits, overcurrent detection, and the H-bridge itself.

Key Points

  1. Block Diagram and System Functionality:

    • Provides an overview of the H-bridge motor controller’s block diagram and the functions of each subsystem.
    • Explains how the subsystems work together to control the motor’s speed and direction.

  2. Subsystem Descriptions:

    • Details the design and operation of each subsystem:
      • Power Supply: Generates the necessary voltage rails for the controller.
      • Clock and Duty Cycle Generator: Provides the timing signals for PWM control.
      • Pulse Width Modulation (PWM): Generates the PWM signals to control the MOSFETs in the H-bridge.
      • Drive Circuit: Amplifies the PWM signals to drive the MOSFET gates.
      • H-Bridge: The core of the motor controller, consisting of four MOSFETs arranged in an H configuration to control the motor’s direction and speed.
      • Overcurrent Detection: Protects the MOSFETs from excessive current flow.

  3. PCB Layout and Schematics:

    • Presents the top view of the PCB layout, showing the placement of components.
    • Provides detailed schematics for each subsystem, illustrating the circuit connections and component values.

  4. Bill of Materials:

    • Lists the Nexperia components used in the design, including MOSFETs and logic ICs.
    • Provides a complete bill of materials for all components required for the H-bridge motor controller.

Conclusion

This chapter serves as a practical guide for designing an H-bridge motor controller using Nexperia MOSFETs and logic ICs. The detailed explanations, schematics, and bill of materials provide a valuable resource for engineers looking to implement similar motor control solutions in their applications.

Chapter 13: Power and Small-Signal MOSFET Frequently Asked Questions (FAQs)

This chapter addresses common questions and concerns regarding power and small-signal MOSFETs. It covers a wide range of topics, from gate drive and thermal considerations to MOSFET body diodes, safe operating areas, avalanche ruggedness, capacitive dV/dt issues, packaging, SPICE models, and MOSFET reliability.

Key Points

  1. Gate:

    • Gate Drive and Threshold Voltage:
      • Importance of proper gate drive voltage for reliable MOSFET operation.
      • Relationship between gate voltage and drain current.
      • Impact of temperature on threshold voltage.
    • Gate Protection:
      • Methods to protect the gate from overvoltage and electrostatic discharge (ESD).
      • Use of Zener diodes, TVS diodes, and resistors for gate protection.

  2. Thermals:

    • Thermal Resistance and Impedance:
      • Explanation of thermal resistance (Rth) and thermal impedance (Zth).
      • How to calculate temperature rise in MOSFETs.
      • Importance of thermal management for reliable operation.
    • Power Dissipation and Temperature:
      • Relationship between power dissipation, temperature, and MOSFET performance.
      • Methods to calculate power dissipation in MOSFETs.

  3. MOSFET Body Diode:

    • Reverse Recovery:
      • Explanation of reverse recovery in MOSFET body diodes.
      • Impact of reverse recovery on switching losses and EMI.
    • Conduction Losses:
      • Calculation of conduction losses in the body diode.

  4. Safe Operating Area (SOA) and Linear Mode Operation:

    • SOA:
      • Definition and importance of the Safe Operating Area.
      • How to interpret SOA graphs.
    • Linear Mode Operation:
      • Explanation of linear mode operation and its challenges.
      • Thermal runaway and how to mitigate it.

  5. Avalanche Ruggedness and Unclamped Inductive Switching (UIS):

    • Avalanche Breakdown:
      • Explanation of avalanche breakdown in MOSFETs.
      • Single-shot and repetitive avalanche events.
    • UIS Test:
      • Description of the UIS test and its significance.
      • How to interpret UIS waveforms.

  6. Capacitive dV/dt Issues:

    • dV/dt-Induced Turn-On:
      • Explanation of how high dV/dt can cause unintended MOSFET turn-on.
      • Methods to mitigate dV/dt-induced turn-on.

  7. Package and Mounting:

    • Package Types:
      • Overview of different MOSFET package types (D2PAK, LFPAK, etc.).
      • Thermal considerations for each package type.
    • Mounting Techniques:
      • Best practices for mounting MOSFETs to PCBs or heatsinks.

  8. SPICE Models:

    • Importance of SPICE Models:
      • How SPICE models are used for circuit simulation.
      • Accuracy and limitations of SPICE models.

  9. MOSFET Silicon Technology:

    • Trench vs. Planar MOSFETs:
      • Comparison of trench and planar MOSFET technologies.
      • Advantages and disadvantages of each technology.

  10. Supply and Availability:

    • Lead Times and Availability:
      • Factors affecting MOSFET lead times and availability.

  11. EMC and ESD:

    • Electromagnetic Compatibility (EMC):
      • How MOSFET switching can generate EMI.
      • Techniques to reduce EMI in MOSFET circuits.
    • Electrostatic Discharge (ESD):
      • How to protect MOSFETs from ESD damage.

  12. Leakage, Breakdown, and MOSFET Characteristics:

    • Leakage Currents:
      • Types of leakage currents in MOSFETs.
      • Impact of temperature on leakage currents.
    • Breakdown Voltage:
      • Definition and significance of breakdown voltage.
    • MOSFET Characteristics:
      • Explanation of various MOSFET parameters and their significance.

  13. MOSFET Reliability:

    • Failure Mechanisms:
      • Common failure mechanisms in MOSFETs.
      • How to improve MOSFET reliability.

Conclusion

This chapter provides a comprehensive overview of common questions and concerns related to power and small-signal MOSFETs. By addressing these FAQs, the chapter aims to equip engineers with the knowledge necessary to design and implement MOSFET-based circuits effectively and reliably.

Chapter 14: Leakage of Small-Signal MOSFETs

This chapter focuses on the leakage currents in small-signal MOSFETs, their impact on applications, and strategies for selecting MOSFETs with low leakage.

Key Points

  1. Leakage Currents:

    • Drain-Source Leakage (IDSS):
      • The current flowing between the drain and source terminals when the MOSFET is off.
      • Increases with temperature due to carrier generation.
    • Gate-Source Leakage (IGSS):
      • The current flowing between the gate and source terminals.
      • Less dependent on temperature compared to IDSS.

  2. Applications:

    • Load Switches:
      • Leakage currents can be a significant concern in load switch applications, especially in battery-powered devices.
      • High leakage can lead to faster battery drain.

  3. Selecting a Low-Leakage MOSFET:

    • Consider Temperature:
      • Choose MOSFETs with low leakage specifications at the maximum operating temperature of the application.
    • Evaluate Gate-Source Leakage:
      • Pay attention to IGSS specifications, especially for applications sensitive to gate leakage.

  4. Nexperia Low-Leakage MOSFET Portfolio:

    • Nexperia offers a range of small-signal MOSFETs with low leakage characteristics.

Conclusion

Understanding and managing leakage currents in small-signal MOSFETs is crucial for optimizing the performance and efficiency of various applications, particularly those that are battery-powered. By carefully selecting MOSFETs with low leakage specifications and considering the temperature dependence of leakage, engineers can design circuits that minimize power consumption and extend battery life.

Chapter 15: DC-to-DC Conversion with Small-Signal MOSFETs

This chapter explores the use of small-signal MOSFETs in DC-to-DC conversion, a critical aspect of power management in electronic devices. It covers various DC-to-DC conversion methods, including buck converters (step-down), boost converters (step-up), and buck-boost converters (step-up/down).

Key Points

  1. DC-to-DC Down-Converter (Buck Converter):

    • Operation: Reduces the input voltage to a lower output voltage.
    • Topology: Employs a switch (MOSFET), diode, inductor, and capacitor.
    • Control: Pulse width modulation (PWM) controls the switch’s on and off times to regulate the output voltage.
    • Efficiency: High efficiency due to the inductor storing and releasing energy.

  2. DC-to-DC Up-Converter (Boost Converter):

    • Operation: Increases the input voltage to a higher output voltage.
    • Topology: Similar to a buck converter but with a different inductor connection.
    • Control: PWM controls the switch to regulate the energy transfer to the output.

  3. DC-to-DC Up/Down-Converter (Buck-Boost Converter):

    • Operation: Can either increase or decrease the input voltage to a desired output voltage.
    • Topology: Combines elements of buck and boost converters.
    • Control: More complex control due to the ability to step up or down the voltage.

  4. Medium Power DC-to-DC Down-Converter using Small-Signal MOSFETs:

    • Application: Demonstrates the use of small-signal MOSFETs in a practical buck converter design.
    • Component Selection: Discusses the choice of MOSFETs, inductor, and output capacitor.
    • Dimensioning: Provides guidance on calculating inductor and capacitor values.
    • MOSFET Losses: Explains how to calculate conduction and switching losses in the MOSFETs.

Formulas

  • Inductor Voltage (Buck Converter): ​
  • Capacitor Current (Buck Converter): ​
  • Duty Cycle (Buck Converter): ​
  • Inductor Voltage (Boost Converter):
  • Duty Cycle (Boost Converter): ​​

Conclusion

DC-to-DC converters are essential for efficient power management in electronic devices. Small-signal MOSFETs play a crucial role in these converters, and understanding their operation and design considerations is vital for creating reliable and high-performance power conversion solutions.

Chapter 16: Load Switches for Mobile and Computing Applications

This chapter discusses load switches, which are used to control the power delivery to specific loads in electronic devices. It covers different types of load switches and their applications in mobile and computing devices.

Key Points

  1. Types of Load Switches:

    • P-Channel MOSFET Load Switch:
      • Uses a P-channel MOSFET as the switching element.
      • Suitable for applications where the gate control voltage is higher than the supply voltage.
    • N-Channel MOSFET Load Switch:
      • Employs an N-channel MOSFET as the switch.
      • Requires a charge pump or bootstrap circuit to generate a gate voltage higher than the supply voltage.
    • Reverse Current Protected Load Switches:
      • Includes a diode to prevent reverse current flow from the load to the supply.
    • Reverse Polarity Protection and Supply OR-ing:
      • Protects against reverse polarity connections and allows multiple power sources to be connected to a load.

  2. Important Parameters:

    • RDS(on): The on-state resistance of the MOSFET switch, affecting power loss and efficiency.
    • Quiescent Current (IQ): The current consumed by the load switch when it is off.
    • Input Voltage Range: The range of input voltages the load switch can handle.
    • Output Current Capability: The maximum current the load switch can deliver to the load.
    • Switching Speed: The time it takes for the load switch to turn on or off.

Conclusion

Load switches are essential components in power management circuits for mobile and computing devices. By understanding the different types of load switches and their key parameters, engineers can select the most suitable switch for their specific application requirements, ensuring efficient power delivery and protection against fault conditions.

Chapter 17: Level Shifting Techniques in I2C-Bus Design

This chapter explores level-shifting techniques used in I2C-bus design, a popular communication protocol used in various electronic devices. It focuses on addressing the challenge of connecting devices with different logic levels.

Key Points

  1. Bidirectional Level Shifter for Fast-Mode and Standard-Mode I2C-Bus Systems:

    • Purpose: Enables communication between devices with different bus voltages (e.g., 1.8V, 2.5V, 3.3V, 5V).
    • Operation: Employs MOSFETs to translate signals between different voltage levels.
    • Benefits: Allows for flexibility and compatibility in I2C-bus designs.

  2. Connecting Devices with Different Logic Levels:

    • Challenges: Direct connection of devices with different logic levels can lead to signal distortion and communication errors.
    • Solution: Level shifters provide a reliable way to interface devices with mismatched voltage levels.

  3. Operation of the Level Shifter:

    • MOSFET-Based Design: Utilizes MOSFETs as voltage-controlled switches to pass or block signals based on the voltage levels.
    • Bidirectional Communication: Supports both signal transmission and reception between devices with different logic levels.

Conclusion

Level shifting is a critical technique in I2C-bus design, enabling seamless communication between devices with different logic levels. By understanding the operation and benefits of bidirectional level shifters, engineers can ensure reliable and efficient data exchange in their I2C-based systems.

Chapter 18: Understanding Power GaN FET Data Sheet Parameters

This chapter provides a guide to understanding the parameters in a power GaN (Gallium Nitride) FET datasheet. GaN FETs are wide-bandgap semiconductor devices known for their high-efficiency and high-frequency operation.

Key Points

  1. Nomenclature:

    • GaN FETs are often integrated with a low-voltage silicon MOSFET to create a cascode configuration, combining the benefits of both technologies.
    • The datasheet parameters are presented for this integrated device.

  2. Pinning Information:

    • Details the pinout of the GaN FET package, including gate (G), source (S), and drain (D) connections.

  3. Two-Chip, Integrated, Normally-Off Power Switch:

    • Describes the cascode configuration, where the GaN FET is stacked on top of a silicon MOSFET.
    • The silicon MOSFET controls the gate of the GaN FET, enabling normally-off operation.

  4. GaN FET Limiting Values:

    • Specifies the maximum ratings for various parameters, including:
      • VDS (Drain-Source Voltage): Maximum voltage the device can block in the off-state.
      • VTDS (Transient Drain-Source Voltage): Maximum transient voltage during switching.
      • VGS (Gate-Source Voltage): Maximum gate-source voltage.
      • Ptot (Total Power Dissipation): Maximum power the device can dissipate.
      • ID, IDM, IS, ISM (Continuous and Pulsed Currents): Maximum allowable currents under different conditions.

  5. GaN FET Static Characteristics:

    • VGS(th) (Gate-Source Threshold Voltage): The gate-source voltage required to turn on the device.
    • RDS(on) (Drain-Source On-State Resistance): The resistance of the device when it is on.

  6. GaN FET Dynamic Characteristics:

    • QG(tot), QGS, QGD (Gate Charges): Charges associated with turning the device on and off.
    • Ciss, Coss, Crss (Capacitances): Input, output, and reverse transfer capacitances.
    • Co(er) (Effective Output Capacitance - Energy Related): Capacitance relevant for energy loss calculations.
    • Co(tr) (Effective Output Capacitance - Time Related): Capacitance relevant for switching time calculations.
    • Qoss, Eoss (Output Charge and Stored Energy): Charge and energy associated with the output capacitance.
    • Switching Time Characteristics: Turn-on and turn-off times.
    • VSD (Source-Drain Voltage): Voltage drop across the body diode.

  7. Qr for GaN FET Switches:

    • Discusses the reverse recovery charge (Qr) of the body diode and its impact on switching performance.

  8. Switching-Node Snubber:

    • Explains the use of a snubber circuit to reduce voltage spikes during switching.

Conclusion

Understanding the parameters in a power GaN FET datasheet is crucial for selecting the right device and designing efficient and reliable high-frequency power conversion circuits. The cascode configuration and the unique characteristics of GaN FETs require careful consideration of various parameters to achieve optimal performance.

Chapter 19: An Insight into Nexperia Power GaN Technology

This chapter provides an overview of Nexperia’s Power GaN technology, focusing on its applications, quality, reliability, and scalability.

Key Points

  1. Introduction:

    • Highlights the growing importance of GaN FETs in power electronics due to their superior performance compared to silicon MOSFETs.

  2. Product Robustness:

    • Emphasizes the robustness of Nexperia’s GaN FETs, achieved through advanced design and manufacturing processes.

  3. Quality and Qualification:

    • Discusses the rigorous quality and qualification procedures followed by Nexperia to ensure the reliability of their GaN FETs.
    • Mentions specific tests like High-Temperature Reverse Bias (HTRB) and High-Temperature Operating Life (HTOL) to assess long-term reliability.
    • Addresses common failure modes and mechanisms in GaN FETs.

  4. Scalability and Growth:

    • Explains how Nexperia’s GaN technology can be scaled to higher power levels and voltages.
    • Discusses the potential for GaN FETs to replace silicon MOSFETs in various applications.

  5. Applications and Performance:

    • Highlights the advantages of GaN FETs in applications like AC-DC and DC-DC converters, power factor correction (PFC), and automotive on-board chargers.
    • Showcases the superior performance of GaN FETs in terms of efficiency, power density, and switching speed.

Conclusion

Nexperia’s Power GaN technology offers a promising alternative to traditional silicon MOSFETs in power electronics. With their robustness, high quality, and scalability, GaN FETs are poised to revolutionize various applications, enabling more efficient and compact power conversion solutions.

Chapter 20: Power GaN Technology: The Need for Efficient Power Conversion

This chapter discusses the growing demand for efficient power conversion and the role of power GaN FETs in meeting this need. It explores the advantages of GaN technology, its scalability, and its applications in various industries.

Key Points

  1. Introduction:

    • Emphasizes the increasing demand for efficient power conversion due to factors like energy conservation, environmental concerns, and the proliferation of electronic devices.

  2. Power GaN FET Switches:

    • Explains the basic operation of GaN FETs and their advantages over silicon MOSFETs, including lower on-state resistance (RDS(on)), faster switching speeds, and higher power density.

  3. Scalability and Growth:

    • Discusses the scalability of GaN technology to higher power levels and voltages, opening up new possibilities for applications.

  4. Applications and Performance:

    • Highlights the use of GaN FETs in various applications, such as data centers, renewable energy systems, industrial motor drives, and automotive electronics.
    • Showcases the performance benefits of GaN FETs in terms of efficiency, size reduction, and cost savings.

  5. Quality and Reliability:

    • Addresses concerns about the quality and reliability of GaN FETs.
    • Mentions ongoing research and development efforts to improve the reliability and longevity of GaN devices.

Conclusion

Power GaN technology is a key enabler for achieving higher efficiency in power conversion systems. With its numerous advantages and growing adoption in various industries, GaN FETs are set to play a significant role in meeting the increasing demand for energy-efficient solutions.

Chapter 21: Circuit Design and PCB Layout Recommendations for GaN FET Half Bridges

This chapter provides practical guidelines for designing half-bridge circuits using GaN FETs. It covers circuit design recommendations, PCB layout considerations, and heat sink connection techniques.

Key Points

  1. Introduction - Diode-Free Bridges:

    • Explains the concept of diode-free half-bridge topologies, where GaN FETs replace traditional silicon diodes for improved efficiency.

  2. Circuit Design Recommendations:

    • Offers solutions to suppress oscillations that can occur in GaN FET half bridges.
    • Discusses gate drive and bootstrap supply considerations.
    • Summarizes circuit design recommendations and lists required and recommended external components.
    • Provides guidance on verifying stable GaN FET operation.

  3. PCB Layout:

    • Recommends optimal pin assignments for GaN FETs in half-bridge configurations.
    • Provides detailed instructions on designing the power loop for minimizing parasitic inductances and improving current flow.

  4. Heat Sink Connection:

    • Explains how to connect the GaN FETs to a heat sink for efficient thermal management.
    • Discusses the gate drive loop layout and its impact on switching performance.
    • Summarizes PCB layout recommendations for optimal thermal and electrical performance.

Conclusion

Designing half-bridge circuits with GaN FETs requires careful attention to circuit design and PCB layout. By following the recommendations in this chapter, engineers can ensure stable operation, minimize losses, and achieve high efficiency in their GaN-based power conversion systems.

Chapter 22: Probing Considerations for Fast Switching Applications

This chapter discusses the importance of proper probing techniques when measuring fast-switching signals in power electronics applications, particularly those involving GaN FETs. It emphasizes that incorrect probing can lead to inaccurate measurements and misinterpretations of circuit behavior.

Key Points

  1. Oscilloscope Probe Ground Spring:

    • The ground spring in oscilloscope probes can introduce inductance, which can distort high-frequency signals.
    • To minimize this effect, it is recommended to use probes with short ground connections or groundless probes.
    • Short ground connections reduce the loop inductance formed by the probe ground and the circuit ground, leading to more accurate measurements.

  2. Oscilloscope and Probes:

    • The bandwidth and rise time of the oscilloscope and probes must be sufficient to capture the fast-switching waveforms accurately.
    • The probe bandwidth should be at least three to five times higher than the signal bandwidth to avoid attenuation and distortion.
    • Active probes are preferred over passive probes for high-frequency measurements due to their lower input capacitance and higher bandwidth.

  3. Probe Positioner:

    • Using a probe positioner is recommended to ensure consistent and accurate probe placement.
    • Proper probe placement is crucial for minimizing parasitic inductance and capacitance, which can affect measurement accuracy.

  4. Additional Considerations:

    • The chapter also mentions the importance of proper grounding techniques and the use of differential probes for measuring voltages across components with high common-mode voltages.

Conclusion

Accurate measurement of fast-switching signals is essential for understanding and optimizing the performance of power electronics circuits. By following the probing considerations outlined in this chapter, engineers can ensure that their measurements are reliable and representative of the actual circuit behavior.

Graph View

πŸ“– MOSFET & GaN FET πŸ“•

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