DC/DC controllers integrate active EMI filter

Texas Instruments (TI) has claimed the industry’s first DC/DC controllers with an integrated active electromagnetic interface (EMI) filter (AEF) to help engineers design the smallest power supply solutions with low electromagnetic interference (EMI). In addition to the integrated AEF, the new family of synchronous DC/DC buck controllers – the LM25149-Q1 and LM25149 – incorporate dual-random spread-spectrum (DRSS) technology, which further helps mitigate EMI.

There are a couple of scenarios by which the new LM25149-Q1 and LM25149 DC/DC controllers help power designers. The devices can either cut the area of the external EMI filter in half and lower the conducted EMI of the power design by as much as 55 dBµV across multiple frequency bands, or achieve a combination of reduced filter size and low EMI, according to TI.

The integrated AEF, by lessening the filtering burden on the passive elements, reduces the size, volume, and cost of the passive EMI filter, enabling engineers to achieve the smallest possible low-EMI power design, said TI.

Ganesh Srinivasan, TI product line manager, wide VIN buck switching regulators, said both the active EMI filter and DRSS, which builds on the company’s previous pseudo-random innovations, are breakthrough technologies that improve the performance of the new device, enabling the 55 dBµV improvement in the performance.

It also is possible to maintain the same performance and reduce the size of the filter,” Srinivasan  added. “The benefit is that you can reduce the size of these bulky [passive] EMI filters in the systems by up to 50% in area and 75% in volume, which are both significant reductions from what it is today.”

(Image: Texas Instruments)

One of the challenges that many OEM designers face is reducing EMI in the power supply, particularly as electronic content increases in applications such as advanced driver assistance systems (ADAS), automotive infotainment and cluster, building automation, and aerospace and defense designs.

“The growing electronic content as well as the increase in switching speeds for DC to DC solutions poses new challenges for power supply designers,” said Cecelia Smith, TI’s vice president and general manager/boost and multi-channel DC/DCs.

Meeting EMI industry standards and lowering conducted and radiated emissions is a key care about for engineers designing power supply systems for automotive and for industrial applications, she added.

“So TI’s approach to help engineers tackle the EMI challenges is two-pronged. The first is to help designers shrink the size of the low-EMI power supply design by reducing the size, component count, and the cost of the passive filter. The second is to help reduce design time and complexity with innovations such as integrated bypass capacitors and integrated active EMI filters,” said Smith.

The most stringent industry requirements for low-EMI designs are Comité International Spécial des Perturbations Radioélectriques (CISPR) 25 Class 5 automotive EMI specifications. A traditional method used to ensure that designs meet conducted EMI specifications includes increasing the size of the external passive EMI filter, which in turn increases the overall power supply solution size, said TI.

These new DC/DC controllers help meet these 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 dBµV at a switching frequency of 440 kHz, relative to a design with the AEF disabled, or as much as 20 dBµV when compared to a design with a typical passive filter,” said TI.

The devices also use additional EMI mitigation techniques to further reduce EMI. In either of the design scenarios noted above, the DRSS technology helps mitigate EMI by an additional 5 dBµV across low- and high-frequency bands, said TI. The buck controllers also feature frequency synchronization to an external clock to further reduce EMI by mitigating undesired beat frequencies in applications sensitive to EMI.

Other features that help increase power density include interleaved dual-phase operation and the integration of the bootstrap diode, loop compensation and output-voltage feedback components, which reduces design complexity and cost. TI noted that engineers have an option to use external feedback and loop compensation to further optimize their designs.

An evaluation module with a full-blown user guide is available to make it easy for power supply designers to evaluate the part, said Srinivasan. “The EVM is set up in a way that you can take full advantage of the device performance so you can test out the low I_Q performance and also both types of EMI improvements,” said Srinivasan.

“At the same time we also encourage our customers to take full advantage of the E2E forums, so through these tools we can help the power supply designers get the full performance out of the part,” he added.

Key features of the LM25149-Q1EVM-2100 evaluation module include a 6-V to 36-V input-voltage range, 5-V output voltage with 1% setpoint accuracy, 8 A of load current, and ultra-low IQ, along with the DRSS and active EMI filtering. The evaluation module is available on TI.com for $75.

Preproduction quantities of the 42-V LM25149-Q1 and LM25149 are available now, only on TI.com, in a 3.5 × 5.5-mm thermally enhanced, 24-pin very thin quad flat no-lead (VQFN) package. Pricing starts at $1.42 and $1.20 in quantities of 1,000, respectively. Volume production is expected in the fourth quarter of 2021. TI plans to introduce a pin-to-pin compatible 80-V version of both devices.