Do You Need an Interleaved DC-DC Converter?

Created: April 29, 2022
Updated: October 10, 2024

Not all designers are power systems engineers, but it still pays to know something about the different ways to build high-efficiency power converters. This includes AC-DC and DC-DC conversion, inverters, PFC circuits, and any number of other equipment for power conversion and efficiency. Even though most designers may not be building power supplies from scratch, they will still need to select them and understand how to integrate them into larger systems, including systems that might interact with the power grid.

With the recent focus on renewable energy and its integration into the existing power grid, especially in the U.S., more designers might be making the switch to smart infrastructure and power electronics. Power conversion is an important part of that integration, and advanced power converter designs will certainly be in high demand as electrical grids are modernized.

One important type of switching converter that designers should be aware of is an interleaved DC-DC converter. This type of converter uses a simple idea to ensure high-efficiency DC-DC conversion, but it is uniquely adaptable to conditions in a renewable grid, a vehicle with multiple batteries, and complex systems with independent loads. These converters can be constructed as a large system from multiple converter stages, but there are also small converters available as integrated circuits. If you decide to use this converter topology in your next system, keep reading to learn about its function and some best practices for component selection.

What is an Interleaved DC-DC Converter?

A DC-DC converter is normally operated with a specific topology when interacting with some input DC source. The input is passed to a 1st stage converter, usually to step down the voltage and output power to a bus. The 2nd stage converter takes power off the 1st stage output bus, and it might convert up or down depending on the needs in that section of the PDN. In the designs we build, we’ll use a switching converter as the first stage converter, then possibly a small LDO regulator IC to step down again to lower logic levels. This gives you the kind of topology shown in the image below:

In the above topology, we have a single-input single-output (SISO) converter, which then connects to a downstream SISO converter, and so on. This usually spans 2 or 3 stages to step down the voltage to various logic levels from a regulated or unregulated DC input, and the DC IN block might be supplied by a rectifier bridge.

What happens if we have multiple isolated loads, multiple sources, or both? This is where interleaving comes in.

MIMO, MISO, or SIMO With Interleaving

Interleaving is a technique where multiple multiple converter stages are used with a single power source to drive multiple loads, with multiple power sources to drive a single load, or some mix of these. An interleaved DC-DC converter uses multiple switching converter stages in parallel connected to an input and output bus. There are three general topologies used in interleaved DC-DC converters:

Single-input multiple-output (SIMO): This is probably the most common type of interleaved DC-DC converter. A single source provides power to multiple converter stages in parallel on a single bus. Each converter stage feeds output power to its own load, which may be galvanically isolated from the remaining loads on the output bus.
Multiple -input single-output (MISO): This is the inverse of a SIMO interleaved DC-DC converter. These converters operate with multiple power sources, where the power sources are generally independent of each other and do not share the same input bus. The output bus is shared in that all converters provide power to a single load.
Multiple-input multiple-output (MIMO): These are probably the most complex interleaved DC-DC converters, but it is the standard type of converter used in a battery charger in solar arrays. Multiple sources are interleaved with multiple power stages, which may then share power to multiple loads.

From the above list, there are two clear situations where you may need to have an interleaved converter. First, you might need to draw power from multiple sources, each at a different voltage, and each requiring different step-up or step-down factors. Second, you may need to power multiple loads with very different impedances. Placing a low impedance load on the output bus from a SISO converter can cause the converter to enter the discontinuous conduction mode, but isolating this load to it’s own converter stage helps you avoid discontinuous operation for all other loads.

The Goal of Interleaving

I mentioned above about ensuring continuous conduction mode operation, but there is more to it than ensuring you operate in this mode. There are examples of converters that operate entirely in the discontinuous mode. The whole point behind interleaving is simple: to reduce the ripple in the delivered current. This is done by offsetting the phases of the switching PWM signals, as shown in the example below.

In this example, we have 2 equal inductors, and the PWM signals sent to the power MOSFETs in each stage of the converter are out of phase by 90 degrees (graphs labelled Q1 and Q2). Here, the total current drawn into the circuit and delivered to the output is the sum of the currents in the output inductors. From adding these two curves in the bottom graph, we can see how the total current will have much lower ripple compared to either of the curves alone.

From the above graph you can infer two effects on the current drawn into the converter and supplied to the load components:

At the input in a SIMO converter: The phase difference in the inductor current causes the total current drawn from the source to become smoother. Because the total current is split to each output, each output current has factor N lower ripple.
At the output in a MISO converter: The phase difference now causes the current delivered to your single load to have lower ripple. The individual currents drawn at the input are lower by a factor N lower ripple.

For this reason, these systems are sometimes called “multi-phase power converters” as you have multiple stages using PWM signals with different phases. These PWM signals may be synced to a master clock, and a phase is added to them individually, possibly in a PWM gate driver for the switching stage.

Power Factor Correction

If your converter will connect to AC power (either as the source or a load), you’ll probably be working at a high enough current to need a power factor correction (PFC) circuit. Just like DC-DC converters can be designed with an interleaved topology, so can the PFC section. In other words, a PFC circuit can be applied to each converter stage, giving a simple way to remove harmonic distortion. This would follow the block diagram shown in the next section.

Component Selection for Interleaved DC-DC Converters

In the above example, I haven’t shown a specific circuit diagram because you can implement interleaving with any of the standard switching converter topologies. Just as an example, consider the block diagram below. There is a PFC section that can accommodate multiple inputs, and the PFC section connects to multiple converters on the output. The converter sections can be in any of the standard switching regulator topologies and driven with a typical PWM driver/controller. Examples of some multichannel PFC/controller components will be shown in the next section.

To date, there is no fully integrated interleaved DC-DC converter. However, like other regulator components, there are a number of ICs that you can use as the main controller/driver for an interleaved switching regulator with standard topology. If you’re ready to start designing an interleaved DC-DC converter, consider these example components. These components can give you a good baseline for a new design, and the application circuits presented below should nicely illustrate how interleaved circuits are built.

Texas Instruments, LM5032

The LM5032 from Texas Instruments is a dual interleaved PWM driver for DC-DC power conversion applications. The device accepts 36 V to 75 V DC power and steps up or down the output voltage with two PWM driving signals. These PWM driver signals can switch MOSFETs in a standard power converter circuit on the output side with programmable frequency up to 2 MHz. The wide input voltage range makes this component applicable to EV/HEV power management systems for battery charging/discharging. Other application areas include industrial systems and telecommunications systems.

Texas Instruments, TPS40322The TPS40322 from Texas Instruments is a dual-phase buck converter driver/controller that can be used in interleaving applications. This controller can provide efficiencies exceeding 90% throughout the input voltage range. The output voltage can be configured with passives on 3 pins, and an external current limiting resistor can be used to set the desired overcurrent protection. Target applications include low-voltage networking equipment and other products found in small data centers.

ON Semiconductor, FAN9672

The FAN9672 from ON Semiconductor is a 2-channel interleaved PFC controller designed to support power converters that interface with the electrical grid. This example application circuit shown below illustrates a standard application with a rectification section and an EMI filter, followed by two converter stages that each have an external driver circuit. Example applications range from HVAC equipment to data center, telecom, and industrial products.

Other Components For Interleaved Power Systems

One of the great advantages of working with an interleaved DC-DC converter topology is that the filtering components you can use in the design can be much smaller. This doesn’t just refer to their component values, it also refers to their physical size. The ripple current on the output is naturally lower thanks to the interleaving strategy, so you don’t need to use larger capacitors and inductors to reduce the total ripple.

Since you’ll need many other components to support an interleaved power system, we’ve compiled a list below to help you get started. The range of power electronics components is already large, and many of these can be adapted for use in interleaved power converters. Some other important components you might need include:

When you’re ready to build an interleaved DC-DC converter, you’ll be able to find these and other important components using the advanced search and filtration features in Octopart. The electronics search engine features in Octopart give you access to updated distributor pricing data, parts inventory, parts specifications, and CAD data, and it’s all freely accessible in a user-friendly interface. Take a look at our integrated circuits page to find the components you need.

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