Low EMI automotive power designs: Page 3 of 7

February 05, 2015 //By Jeff Gruetter
Low EMI automotive power designs
Jeff Gruetter, Product Marketing Engineer, Linear Technology Corporation considers low EMI automotive power design issues.
So minimizing EMI is imperative.

Historically, the solution was to use an EMI shielding box, but this adds significant cost and size to the solution footprint while complicating thermal management, testing and manufacturability. Another potential solution within the power management IC is to slow down the switching edges of the internal MOSFET. However, this has the undesired effect of reducing the efficiency and increasing the minimum on time which compromises the IC’s ability to deliver low duty cycles at switching frequencies at, or above 2MHz. As both high efficiency and small solution footprints are desired, this isn’t a viable solution.

Fortunately, some unique power IC designs have been introduced to enable fast switching frequencies, very high efficiency and low minimum on-times concurrently. These designs generally offer in excess on 20dB lower EMI emissions while offering 2MHz switching frequencies and 95% efficiency. Some also have spread spectrum capability which can lower EMI emissions an additional 10dB. These effects are accomplished with no additional components or shielding, offering a significant breakthrough in switching regulator design.
 
High Efficiency Operation

High efficiency operation of power management ICs in automotive applications is important for two main reasons. First, the more efficient the power conversion, the less energy is wasted in the form of heat. Since heat is the enemy of long term reliability of any electronic system, it must be managed effectively which generally requires heat sinks for cooling, which adds complexity, size and cost to the overall solution. Secondly, any wasted electrical energy in hybrids or EVs will directly reduce their driving range. Until recently, high voltage monolithic power management ICs and high efficiency synchronous rectification designs were mutually exclusive as the required IC processes could not support both goals.

Historically, the highest efficiency solutions were high voltage controllers which used external MOSFETs for their synchronous rectification. However, these configurations are relatively complex and bulky for applications under 25W when compared to a

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