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    Hello and welcome to the Troubleshooting Buck Design Issues video series. I'm Sam Jaffe, applications engineer at Texas Instruments in the Greater Than 30 Volt Buck Converters and Controllers Group. This series of videos will discuss common issues and debug tips and tricks for buck converters and controllers.

    The first video gives a quick introduction to buck converters and controllers and explains the necessity of troubleshooting. You will learn why this information is useful. Then, you will learn what a buck converter is, when you would use one, how it works, and a quick overview of what could typically go wrong to create an issue.

    The second video discusses what can go wrong with a schematic. This includes picking the best converter for your application, picking optimal components around the converter, and the common issues and how to resolve them.

    The third video discusses issues with the layout. This includes proper component placement, the priority of placing components, and the common issues and how to resolve them. So let's get started.

    First, why is this information important? Every circuit requires power. And a buck converter is an extremely popular method of delivering high efficiency, step-down voltage regulation. This means you will probably encounter a buck or already encounter bucks on a day-to-day basis.

    You want to be sure your design will work, which means you will perform schematic reviews and layer reviews. The information in these videos will ensure your reviews are quick and effective.

    Sometimes the design does not work, which leads to debugging and troubleshooting to find the root cause and fix the issue. This information will speed up the troubleshooting process by giving you a more intuitive understanding of what to look for and what may be going wrong depending on what you see. Mastering this information means you will be able to solve issues quickly, and you won't have to rely on support, which means you can get more done in less time.

    So what is a buck? A buck converter is one of many options to regulate power from the voltage to a lower voltage . A common solution is a linear regulator, which acts as a variable resistor to create a voltage drop from input to output in order to keep the output regulated regardless of changes in input. This is very simple. Typically, low cost, low noise.

    But the efficiency can be very bad, especially if there is a large difference in voltage between the input and output. This poor efficiency leads to heat dissipation, which limits linear regulators to low current applications, typically no more than 1 amp.

    A buck converter is a switching topology, which has a theoretical maximum efficiency of 100%. This means it is suitable for a higher current applications. But this efficiency comes with drawbacks of increased complexity, increased cost, and more noise.

    Other topologies like buck boosts, fly backs, forwards, full bridges, and more also have a high efficiency that can be suited for currents higher than a buck. They can be more complex and can have higher costs than a buck.

    There are many options, but a buck is typically the most common next step from linear regulator when increasing power capability. We're discussing the buck converter. We will go into detail on the less simple and the noisy aspects of the buck topology and explain how to anticipate and fix any issues that may come up from these potential drawbacks.

    So how does a buck work? Put simply, the high-side FET turns on, and the low-side FET turns off. The switch node voltage is now V in. The inductor voltage VL is now V in minus V out. This causes the inductor current to ramp up.

    Next, the high-side FET turns off and the low-side FET turns on. The switch node voltage is now ground. The inductor voltage VL is negative V out. This causes the inductor current to ramp down.

    Then, we repeat at a frequency typically in the hundreds of kilohertz to a couple of megahertz. This creates an output voltage proportional to V in and the duty cycle. This duty cycle is 50%. So we would expect V out to be 50% of V in. The upper limit on efficiency, if everything was ideal, is 100%.

    Now that we know how a buck topology works, what can go wrong? Here, we show a simplified schematic of a buck. A real buck requires more surrounding components to achieve proper operation.

    So we can have an issue with the schematic. We can pick the wrong part for the application. Or we could pick the wrong components around the IC.

    We can also have an issue with the layout, which is how all the components are placed around the IC physically on the board. The circuit will always have parasitics and coupled noise. But oftentimes, a poor layout can cause excessive parasitics and coupled noise to affect the operation of the circuit beyond acceptable margin.

    The next video in the series, we'll go into detail on the schematic side. And the video after that, we'll detail the common layout issues. Stay tuned for these videos to learn more about troubleshooting buck converters and controllers to ensure your designs work the first time, all the time.