System Analysis Knowledge Bytes: Thermal Effects on Voltage Margins with Celsius PowerDC

The System Analysis Knowledge Bytes blog series explores the capabilities and potential of the System Analysis tools offered by Cadence. In addition to providing insight into the useful features and enhancements in this area, this series aims to broadcast the views of different bloggers and experts who share their knowledge and experience on all things related to System Analysis.

V = IR. Almost every engineer has seen this simple equation. Ohm's Law is one of the foundational equations in physics and electronics. It states that a voltage drop across two nodes can be calculated by multiplying the current flowing between the nodes with the resistance between the nodes. Simple, right? But what if we add a temperature-dependent coefficient to the resistance? What if we add a condition that as the temperature of a conductor increases, so does its resistance?

Suddenly, it's not so simple anymore. In real-world engineering, temperatures can affect the voltage margins of a design. The new DC and Thermal Analysis with Celsius PowerDC course covers the nuances of electrical and thermal simulations, including co-simulations, in depth.

What's the Issue?

As Ohm's Law dictates, if a current flows through any conductor with resistance, there's an expected voltage drop across that conductor. However, due to its inherent resistance, heat is also generated through that conductor, which is known as Joule heating.

The real issue is that when a conductor heats up due to Joule heating, its resistance also increases. And as the resistance of the conductor increases, both the voltage drop across the conductor increases, and the conductor continues to get hotter. It's a self-feeding system that needs to find an equilibrium with the ambient environment to stabilize. Not only are thermal constraints a concern for the design, but the increased voltage drop seen across all the conductors of a system could affect the voltage margins of the design, especially for those in enclosed spaces with limited cooling.

What's the Fix?

Celsius PowerDC and the Celsius suite of thermal solvers offer a powerful solution to this dilemma. If an electrothermal co-simulation is properly set up, the tool will simulate an electrical solution with temperature awareness and then a thermal solution that factors in an ambient environment, including temperature and airflow. It will then feed the temperatures back into the electrical solver and continue to iterate this process until the system converges on a solution.

More advanced solutions, including a chassis with fans and openings, can be modeled to effectively model the electrical and thermal performance of a system that has active cooling, like what is seen in a server rack. The additional considerations of temperature in electrical designs bring more confidence in the design process through simulation and are showcased in the new power integrity course DC and Thermal Analysis with Celsius PowerDC.

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