Minimize EMI in automotive environments

January 09, 2014 // By Tony Armstrong
While switching power supply layout is not a “black” art, it can often be overlooked in the initial design process. Nevertheless, since functional and EMI requirements have to be met, what is good for functional stability of the power supply is also usually good for its EMI emissions as well.

Printed circuit board layout determines the success or failure of every power supply. It sets functional, electromagnetic interference (EMI) and thermal behaviour. While switching power supply layout is not a “black” art, it can often be overlooked in the initial design process. Nevertheless, since functional and EMI requirements have to be met, what is good for functional stability of the power supply is also usually good for its EMI emissions as well. It should also be note that good layout from the beginning does not add any cost, but can actually provide cost savings, eliminating the need for EMI filters, mechanical shielding, EMI test time and PC board revisions.

Moreover, the potential problem for interference and noise can be exasperated when multiple DC/DC switchmode regulators are paralleled for current sharing and higher output power. If all are operating (switching) at a similar frequency, the combined energy generated by multiple regulators in a circuit is then concentrated at one frequency. Presence of this energy can become a concern especially if the rest of ICs on the PC board as well as other system boards are close to each other and susceptible to this radiated energy. This can be particularly troubling in automotive systems which are densly populated in and are often in close proximity to audio, RF, CAN bus and various radar systems.

Addressing Switching Regulator Noise Emissions

In an automotive environment, switching regulators usually replace linear regulators in areas where low heat dissipation and efficiency are valued. Moreover, the switching regulator is typically the first active component on the input power bus line, and therefore has a significant impact on the EMI performance of the complete converter circuit.

There are two types of EMI emissions; conducted and radiated. Conducted emissions ride on the wires and traces that connect up to a product. Since the noise is localized to a specific terminal or connector in the design, compliance with conducted emissions

Design category: