DC/DC controllers’ integrated EMI filter aids tiny low-power designs

A series of synchronous DC/DC buck controllers that enable engineers to shrink the size of the power-supply solution and lower its electromagnetic interference (EMI) have been launched by Texas Instruments. Featuring an integrated active EMI filter (AEF) and dual-random spread-spectrum (DRSS) technology, the LM25149-Q1 and LM25149 enable engineers to cut the area of the external EMI filter in half, lower the conducted EMI of the power design by up to 55 dB-microvolt across multiple frequency bands, or achieve a combination of reduced filter size and low EMI.

The most stringent industry requirements for low-EMI designs are Comité International Spécial des Perturbations Radioélectriques (CISPR) 25 Class 5 automotive EMI specifications. The LM25149-Q1 and LM25149 buck controllers help engineers meet those requirements by mitigating conducted EMI across multiple frequency bands. The integrated AEF helps detect and reduce conducted EMI in the low-frequency band of 150 kHz to 10 MHz, enabling engineers to attenuate EMI by up to 50 dB-microvolt at a switching frequency of 440 kHz, relative to a design with the AEF disabled, or up to 20 dB-microvolt when compared to a design with a typical passive filter. In both design scenarios, the DRSS technology can help mitigate EMI by an additional 5 dB-microvolt across low- and high-frequency bands.

To further reduce EMI, both buck controllers feature frequency synchronisation to an external clock, helping engineers mitigate undesired beat frequencies in applications sensitive to EMI.

The LM25149-Q1 and LM25149 buck controllers allow engineers to meet challenging EMI standards and shrink solution size by reducing the area and volume of the passive EMI filter. Compared to competing solutions, engineers can achieve maximum savings of nearly 50 per cent in area and more than 75 per cent in volume of the front-end EMI filter at 440 kHz. By lessening the filtering burden on the passive elements, the integrated AEF reduces their size, volume and cost, enabling engineers to achieve the smallest possible low-EMI power design.

Both controllers further increase power density by enabling interleaved dual-phase operation and by integrating the bootstrap diode, loop compensation and output-voltage feedback components, which in turn reduces design complexity and cost. Engineers also have an option to use external feedback and loop compensation to further optimise their designs.


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