How to answer four common questions about power module stray inductance

Stray inductance is the sum of all unwanted inductance elements from components, wires, copper planes, and traces in a current path. Stray inductance in power modules has a huge impact on switching characteristics, such as:

• Switching speed
• Switching loss
• Voltage overshoot

Measuring the stray inductance of a power module is a complex and important task. Instead of extracting the stray inductance by measurement on a prototype, it would be beneficial to use simulation for that. Let’s look at four common questions you need to answer about power module stray inductance.

1. What is the maximum stray inductance of the power module?

Determining the maximum stray inductance of a power module is a complex task. It requires an understanding of the power module’s structure, including its components and their electrical characteristics. To identify the maximum stray inductance of a power module, the following steps should be taken:

• Examine the power module components and their circuitry.
• Analyze the inductance of all components in the power module, including wires, copper planes and traces.
• Determine if any additional elements such as magnetic fields or other objects are contributing to the stray inductance.
• Use simulation tools to get an accurate measurement of the maximum stray inductance of the power module.

By following these steps, you can accurately determine the maximum stray inductance of any power module. With HyperLynx Advanced Solvers, the board parasitics, including the stray inductance, can be calculated, and back annotated to the circuit level simulation in Xpedition AMS as a SPICE netlist. The exported SPICE netlist includes the parasitics between each component pin. During the board level simulation, the parasitics’ effect on the switching behaviour and voltage overshoot can be analyzed. This will allow for better prediction and optimization of design parameters before building a prototype.

2. How parallel devices influence the stray inductance

Parallel devices, such as multiple power modules, influence the stray inductance of a power system. This is due to the fact that when multiple power modules are connected in parallel, they all share the same current path. As a result, each module contributes to the total stray inductance of the power system.

To minimize the effect of parallel devices on the stray inductance, it is important to consider their impact when designing a power system. Consider using simulation tools to accurately determine the total stray inductance of multiple power modules connected in parallel and identify any potential issues before building a prototype.

3. How does the wire bond width influence stray inductance?

Wire bond width has a significant influence on the stray inductance of a power module. As the width of the wire bonds increases, it results in an increased amount of inductive reactance on the path of current flow. This, in turn, causes an increase in stray inductance.

As the parasitics extraction in HyperLynx Advanced Solvers also includes bond wires, their effect will be taken into account when simulating the module’s behavior with board parasitics.

4. What is the maximum voltage overshoot of the power module?

The maximum voltage overshoot of a power module is determined by analyzing its stray inductance and current slew rate, and this can be done using simulation tools. To accurately determine the maximum voltage overshoot, the following steps should be taken:

• Identify the output parameters of the power module, such as switching speed, switching loss and voltage overshoot.
• Use simulation tools to determine the total stray inductance of the power module.
• Calculate the maximum voltage overshoot based on the power module’s output parameters and its simulated stray inductance.

By following these steps, you can accurately determine the maximum voltage overshoot of any power module using simulation tools. This will allow you to optimize the power module’s design parameters before building a prototype.

Power modules are a key component in power electronics and understanding their stray inductance is essential to accurately determining the maximum voltage overshoot of any system. By following the steps outlined above, you can use simulation tools like HyperLynx Advanced Solver Fast 3D, to identify potential issues with your design before building a prototype. With this knowledge, designers have more control over optimizing design parameters for better efficiency and performance while ensuring safety standards are met. Keep these principles in mind when designing your next power module and be sure to leverage all available resources including simulation software for accurate measurements.

To learn more about designing power modules, download our whitepaper, Power modules: A four-dimensional design challenge calls for a holistic design and verification approach.