This article provides a brief overview of the buck-boost topology as a power management tip and introduces the latest new regulators from Analog Devices (ADI) that support Silent Switcher® technology. Combining the buck-boost architecture with Silent Switcher technology enables the highest power conversion efficiency with very low electromagnetic interference (EMI).

■ Wide range of input processing power supply required

Depending on the application, there are many cases where the voltage needs to be increased or decreased.

For example, if you need to generate a 12V output from an input voltage range of 6V to 24V, you need a power supply that can handle a wide range of inputs.

There are various voltage conversion architectures that can handle these up and down voltage conversions.

Representative topologies include transformer-based topologies such as the flyback regulator, the single-ended primary inductor converter (SEPIC) topology, and the 4-switch buck-boost topology.

Among these, the 4-switch buck-boost is a very sophisticated approach. It requires four switches but uses only one inductor. Figure 1 shows this circuit structure. The coil is controlled by four switches, operating as a buck switching regulator for downconversion or a boost switching regulator for upconversion. This architecture offers high power conversion efficiency and makes circuit applications very simple.


A switched-mode buck-boost converter operates at a specific switching frequency and generates pulsed currents in the internal circuitry of the voltage converter.

This pulse current occurs on the input side in buck mode when the input voltage is higher than the output voltage, and on the output side in boost mode when the input voltage is lower than the output voltage.

This pulsed current induces a pulsed magnetic field, which generates electromagnetic interference (EMI).

Analog Devices' Silent Switcher® technology enables the design of switching-mode power converters with excellent electromagnetic compatibility (EMC).

This technique splits the pulse current into two conducting paths, each with high symmetry.

As a result, the amplitude of the pulse current is halved, and most of the generated magnetic field is canceled out by symmetry.

Figure 2 shows an example of this technology applied to a buck-boost controller. The red lines represent the paths of the pulse currents, and the magnetic fields they generate are canceled out by the symmetrical structure.


Figure 2 shows a total of eight switching transistors. A buck-boost circuit based on Silent Switcher technology actually requires only four switches, as does a conventional buck-boost topology. However, four additional switches are shown in this figure to facilitate the visualization of the symmetrical pulse current path.

The combination of buck-boost regulator and silent switcher technology now allows the development of step-up/down converters with very good EMC performance.

For best EMC performance, it is effective to use a Silent Switcher 2 regulator with integrated decoupling capacitors.

These capacitors, shown in Figure 2, are already integrated into devices such as the LT8350S.

This integration further reduces radiated noise by reducing parasitic effects in the pulse current path compared to conventional products that use external decoupling capacitors.

A version that uses external decoupling capacitors is the LT8350.

Figure 3 shows a circuit utilizing the LT8350S buck-boost switching regulator.

The device can handle up to 6A of switch current and has an input voltage range of 3V to 40V. To further reduce EMI generated, spread spectrum frequency modulation (SSFM) is optionally available.

The circuit in Figure 3 shows the external circuit configuration and the LTspice® simulation model available for free through the ADI website.


■ Buck-boost switching regulator, suitable for voltage conversion circuits

Buck-boost switching regulators are ideal for voltage conversion circuits that require the output voltage to be both higher and lower than the input voltage. Using the latest ICs, such as Analog Devices' (ADI) LT8350S, you can design switch-mode voltage converters that leverage Silent Switcher technology to achieve exceptional EMC performance.

※ About the author
Frederik Dostal is a power management expert with over 20 years of experience in the industry. After studying microelectronics at the University of Erlangen in Germany, he joined National Semiconductor in 2001, where he gained extensive experience implementing power management solutions on customer projects as a Field Application Engineer (FAE). While at National Semiconductor, he worked in Phoenix, Arizona, for four years as an Application Engineer, focusing on switch-mode power supplies (SMPS). He joined Analog Devices in 2009 and has since held various positions across product lines and European technical support. Currently, he is a power management specialist at ADI's Munich office, leveraging his extensive design and application knowledge.