Reduce external passive EMI filter size by 50%

When working on low-electromagnetic interface (EMI) applications design engineers are required to reduce the EMI of their designs and shrink the solution size. There are a few methods a design engineer can take in order to accomplish this like Front-end passive filtering, however this method can be at odds with increasing the power density of low-EMI designs, especially with the effects of increased switching speeds on the overall EMI signature. Passive filters can be bulky and can take up as much as 30% of the total volume of the power solution, so there still needs to be a viable solution for minimizing the volume of the EMI filter while simultaneously increasing power density.


An active EMI filter senses any noise or ripple from the DC/DC switching regulator and injects a signal 180º out of phase to cancel the noise, effectively minimizing conducted emissions and allowing for a 50% reduction in passive EMI filter size.



42-V synchronous buck DC/DC controller with ultra-low IQ & intergraded active EMI filter


The AEF function that is integrated into LM25149 injects a signal 180 degrees out of phase with the noise generated by the DC/DC, reducing conducted emissions by as much as 50dBμV and allowing for the use of a much smaller external filter (50% by area and up to 75% by volume). This allows the customer to meet challenging EMI standards while simultaneously maximizing power density and lowering overall power supply solution cost.



42-V automotive synchronous buck DC/DC controller with ultra-low IQ & integrated active EMI filter


The LM25149-Q1 42-V automotive buck controller is the industry’s first switching regulator with an active EMI filter integrated into the IC.


EMI Training Series

Texas Instruments has designed an in-depth training series on Designing a low EMI power supply, recognizing the challenges design engineers face when balancing size and EMI emissions.


Additional Resources

Texas Instruments (TI) has an in-depth analysis of how to reduce EMI and shrink power-supply size with an integrated active EMI filter in their recent  technical article.


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