DC-DC conversion from car battery meets stringent EMI standards: Page 5 of 5

September 23, 2020 //By Zhongming Ye, Analog Devices
DC-DC conversion from car battery meets stringent EMI standards
Noise-sensitive applications in harsh automotive and industrial environments require low noise, high efficiency buck regulators that can fit into tight spaces. This article presents state-of-the-art solutions that save space while also achieving low EMI and excellent thermal performance.

Another common issue with high switching frequency is that switching losses tend to increase. The switching related losses include the switch turn on loss, turn off loss, and gate drive loss—all roughly linearly dependent on the switching frequency. Nevertheless, these losses can be improved with faster switch turn-on and turn-off times. The LT8636 switching turn-on and turn-off times are very short, less than 5 V/ns, resulting in minimum deadtime and minimum diode time, reducing the switching losses at high frequency.

The LT8636 used in the solutions here is assembled in a 3 mm × 4 mm LQFN, using a monolithic construction with integrated power switches and inclusion of all necessary circuitry yields a solution with a minimal PCB footprint. The large area exposed ground pad under the IC guides heat to the PCB through a very low thermal resistance (26°C/W) path, reducing the need for additional thermal management. The package is designed for FMEA compatibility. Silent Switcher technology reduces the PCB area of the hot loop, so radiated EMI with such high switching frequency can be easily addressed with simple filters, as shown in Figure 3.

Conclusion

With careful IC selection, it is possible to produce compact high performance power supplies for automotive applications without the usual trade-offs. That is, high efficiency, high switching frequency, and low EMI can all be achieved. To exemplify the types of compact designs that can be achieved, the solutions shown in this article use the LT8636, a 42 V, 5 A continuous/7 A peak monolithic step-down Silent Switcher regulator in a 3 mm × 4 mm LQFN package. In this IC, the VIN pins are split and placed symmetrically on the IC, splitting the high frequency hot loop, mutually cancelling the magnetic fields to suppress the EMI radiated emission. Also, a synchronous design and fast switching edges improve efficiency at heavy load, while the light load efficiency benefits from the low ripple Burst Mode operation.

The LT8636 also fits automotive applications with a 3.4 V to 42 V input range and low dropout, enabling it to operate in automotive crank or load dump scenarios. In automotive applications, system designers are accustomed to facing a number of trade-offs when trying to shrink power supply solution size, but with the designs shown here, designers can achieve all their performance goals without trade-offs.

About the Author

Zhongming Ye is an applications engineering manager for power products at Analog Devices in Santa Clara, California. He has been working at Linear Technology (now part of Analog Devices) since 2009, providing application support for various products including buck, boost, flyback, and forward converters. His interests in power management include high performance power converters and regulators of high efficiency, high power density, and low EMI for automotive, medical, and industrial applications. Prior to joining Linear Technology, he worked at Intersil for three years on PWM controllers for isolated power products. He obtained a Ph.D. degree in electrical engineering from Queen’s University, Kingston, Canada. Zhongming was a senior member of the IEEE Power Electronics Society. He can be reached at zhongming.ye@analog.com.

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