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DC/DC controllers can shrink low-EMI power designs
Two synchronous 42V DC/DC buck controllers released by Texas Instruments (TI) are claimed to enable engineers to achieve the smallest low-EMI power designs. In particular, designers can optimise the size and EMI of the power supply in industrial and automotive electronics.

The LM25149-Q1 and LM25149 buck controllers have an integrated active EMI filter (AEF) and dual-random spread-spectrum (DRSS) technology to halve the area of the external EMI filter, lower the conducted EMI of the power design by as much as 55dBµV across multiple frequency bands, or a combination of the two.

As electronic content increases in advanced driver assistance systems (ADAS), automotive infotainment and cluster, building automation, and aerospace and defence designs, reducing EMI in the power supply is a growing design challenge, says TI. Conventional ways to ensure that a design meets conducted EMI specifications are to increase the size of the external passive EMI filter, but this increases the overall power supply size. Integrating the AEF allows engineers to meet EMI standards while increasing power density.

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

Both buck controllers further reduce EMI via frequency synchronisation to an external clock. This helps engineers mitigate undesired beat frequencies in applications sensitive to EMI.

The buck controllers also allow engineers to achieve maximum savings of nearly 50% in area and over 75% in volume of the front-end EMI filter at 440 kHz, compared with competing, available solutions. By reducing the filtering operation of the passive elements, the integrated AEF reduces their size, volume and cost, explains TI.

Power density is further increased through interleaved dual-phase operation and by integrating the bootstrap diode, loop compensation and output voltage feedback components. This reduces design complexity and cost and gives engineers the option to use external feedback and loop compensation.

Pre-production quantities of the LM25149-Q1 and LM25149 are available now in a 3.5 x 5.5mm thermally enhanced, 24-pin very thin quad flat no-lead (VQFN) package.

Evaluation modules (LM25149-Q1EVM-2100) are also available.

Volume production is expected in Q4 2021 and the company is also working on a pin-to-pin compatible 80V version of both devices.


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