| SEPIC topology, provides stable output voltage
| SEPIC, different power supply even with different input voltages
| ADI LT8711, SEPIC-enabled DC-DC controller

Products that support synchronous SEPIC topology are not that common.

Analog Devices (ADI)'s LT8711 is a DC-DC controller capable of synchronous buck, boost, SEPIC (Single-Ended Primary-Inductor Converter), ZETA topologies, and asynchronous buck-boost topologies.

The SEPIC topology is useful in that it can provide a stable output voltage even if the input voltage drops significantly lower than the output or rises significantly higher than the output.

It is particularly important for automotive applications where cold cranking or load dumps may occur, and for industrial applications that use long power lines and where power outages may occur in factory environments.

Equipment used in the oil and gas sector can increase reliability by using SEPIC converters.

This is because when multiple power supplies are used to power the main load, SEPIC can supply power to the load using a different power source even if the input voltage is different, in the event of a problem with one power source.

Figure 1 shows a synchronous SEPIC converter adopting the LT8711 for the powertrain, using the following components.

▲ Two uncoupled inductors L1 and L2
▲ Driven using N-channel MOSFET MN1 and BG pins
▲ Driven using two synchronous P-channel MOSFETs MP1 and MP2 and the TG pin
▲ Decoupling capacitors C1, C2, C3
▲ Input and Output Filters

Figure 2 shows the efficiency of this converter at an input voltage of 14V. By using a synchronous method, high efficiency is achieved with a peak efficiency of 93.4%.

Figures 3 and 4 show that stable output regulation is maintained even when the input voltage drops lower or rises higher than the output.

For this design, the output current of the demo circuit DC2493A was modified to be increased from 4A to 6A. Also, MOSFETs MN1 and MP1 and inductor L2 were replaced with the parts shown in Figure 1.

This design was evaluated using a modified DC2493A demo circuit.
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Figure 5 shows a thermal image of this board.

The LT8711 demo circuit provides an LTspice model of a similar solution. The LT8711 data sheet also explains how to properly select SEPIC powertrain components.

The following are formulas for calculating peak voltage and current to help understand the basic functions of this topology.

The LT8711 is highly versatile and flexible, designed to enable synchronous buck, boost, SEPIC, ZETA, and asynchronous buck-boost converters.

By using synchronous SEPIC, stable output can be provided with high efficiency even within a fluctuating input voltage range. This point is important for automotive and industrial applications.










This article summarizes 'High Efficiency Synchronous SEPIC for Automotive and Industrial Installations' by Victor Khasiev, Senior Application Engineer at Analog Devices.