TI highlights low EMI power trend in automotive, industrial applications

Article By : Maurizio Di Paolo Emilio

The key challenges of power management lie in the following: low EMI, low power density, but also low IQ, accuracy, noise and isolation.

The key challenges of power management lie in the following five trends: low electromagnetic interference (EMI), low power density, but also low IQ, accuracy, noise and isolation. During the last press briefing, Texas Instruments (TI) focused on the low EMI power trend, which minimizes the interference of power supplies with other system components and simplifies the engineers’ design and qualification processes.

Cecelia Smith, vice president and general manager Boost and Multi-Channel DC/DCs and Ganesh Srinivasan, product line manager, Wide VIN Buck Switching Regulators at Texas Instruments, highlighted how meeting industry EMI standards and lowering conducted and radiated emissions is a key concern for engineers designing power systems for automotive and industrial applications. Increasing electronic content as well as increasing switching speeds for DC-to-DC solutions pose new challenges for power supply designers.

The development of new packaging and new semiconductor innovations and new modeling techniques for power management offer many tools for lowering EMI. Crucially, it is important to reduce the low-EMI power supply design’s size, reducing the number of components and the cost of the passive filter. This can also help reduce design time and complexity.

EMI filtering

Designers working on low electromagnetic interference applications typically face two significant challenges: the need to reduce the EMI of their designs and, at the same time, reduce the size of the power supply solution.

In a system requiring electromagnetic compatibility (EMC), components that act as electromagnetic sources are designed in a way that reduces switching emissions. EMI is the electromagnetic energy produced as an unwanted by-product of switching currents and voltages. Conventional methods of reducing EMI include the use of passive and active filters (Figure 1).

Passive filters tend to be bulky, resulting in large power supply solutions. Passive filtering employs inductors and capacitors for filtering, while active filtering employs an analog circuit to generate an opposite phase current. Active EMI filtering (AEF) aims to reduce size and therefore cost of the power supply solution, while providing EMI performance that meets industry requirements. Two significant examples are shown in Figure 2; the active part employs an operational amplifier circuit (op-amp) as a capacitive multiplier to replace the filter capacitor (CF) in the passive design. The impedances use relatively low capacitance values with small component footprints.

Figure 1: Example of EMI sources in an SMPS (Source: TI)
Figure 2: Conventional passive filtering (a) and active filtering (b) circuit implementations (Source: TI)

Figure 3 compares the printed circuit board (PCB) layout of the passive and active filter stages in Figure 1. The inductor footprint is reduced from 5mm by 5mm to 4mm by 4mm. In addition, two 1210 capacitors are replaced by several small 0402 components with stable value for detection, injection and AEF compensation. The integrated active EMI filter reduces the footprint of the solution by almost 50%, while the volume decreases by more than 75%.

Figure 3: PCB layout size comparison of passive (a) and active (b) filter designs (Source: TI)

DC/DC buck controller with an integrated active EMI filter

During the briefing, the speakers highlighted how TI’s DC/DC buck controllers with an integrated active EMI filter, the LM25149-Q1 and LM25149,can detect noise or ripple voltage at the device’s input and feed a signal that is out of phase with this noise to cancel it out, thus achieving an improvement in EMI performance. “This device includes another revolutionary technology, Dual Random Spread Spectrum (DRSS), which builds on our previous pseudo-random innovations to enhance the technology further and improve the performance of our device. Thus, between the active EMI filter and DRSS techniques, this device can help power supply designers achieve an improvement of up to 55 dB per microvolt by reducing filter size,” said TI.

Reducing filter size is a major benefit, especially with the increase in electronics in both the automotive and industrial sectors. “In another one of our flagship low-EMI devices, the LMQ61460, we have integrated bypass capacitors that help reduce switching loop parasitic inductance and improve EMI (electromagnetic interference) performance. And the other unique thing combined with the integrated bypass capacitors, is our HotRod™ package with a very optimized pinout, so engineers can get the best EMI performance out of the device,” said TI.

Reducing EMI in the power supply is a growing design challenge, especially with the increased electronic content in advanced driver assistance systems (ADAS), infotainment, and automotive clusters. A traditional way of ensuring that a design meets the conducted EMI specification involves increasing the size of the external passive EMI filter, which in turn increases the overall size of the power solution. By integrating active EMI filtering into the LM25149-Q1 and LM25149 buck controllers, TI enables engineers to meet EMI standards while increasing the power density of their design (Figure 4).

Figure 4: Typical application schematic of the LM25149-Q1 (Source: TI)

Maintaining low EMI in the power supply and achieving a small solution are usually at odds in switching power supply designs. The LM25149-Q1 and LM25149 buck controllers allow engineers to meet tough EMI standards and reduce the size of the solution by reducing the area and volume of the passive EMI filter. Compared to previous solutions, engineers can achieve maximum savings of nearly 50 percent in area and over 75 percent in volume of the 440 kHz front-end EMI filter.

This article was originally published on Power Electronics News.

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