Analog Applications Spotlight: Anthony Fagnani

I'm pleased to welcome Anthony Fagnani to the Power House blog. Anthony is the mind behind the article "Synchronous rectification boosts efficiency by reducing power loss" featured in TI's Analog Applications Journal newsletter.

Welcome Anthony!

What is the problem/challenge you saw that spurred you to write “Synchronous rectification boosts efficiency by reducing power loss”?  As an applications engineer at Texas Instruments, my group had just released our first wide VIN synchronous boost controller, the TPS43060 and TPS43061. I really wanted to take a closer look at the benefits of synchronous rectification in a step-up application. While testing, I thought others might be curious also. That’s when I decided I would write it up to share and hopefully help others.

Measured efficiency and power loss in a low-duty-cycle application

What was the most difficult aspect of the topic you wrote about and why? The topic was pretty straight forward to write up and test. The hardest part may have been finding the time to do so!

Who and what application do you think this article is best suited for? This article is applicable to anyone looking to design a step-up converter at a high current where synchronous rectification can provide a benefit. This covers a very wide range of applications from industrial to those powered by a battery. I hope this will provide others with a fair comparison to aid in choosing a solution which best fits their needs.

Did you learn anything as you researched and wrote this article that you did not know before? I was at first surprised by how little of a difference there was in efficiency for a high duty-cycle example. There are some slight differences between the controllers which lead to this. One difference is the location of the current sense resistor. The synchronous solution still however, has the benefit of a smaller footprint.  Overall, I was lucky to have the development go very smoothly, which doesn’t always happen on engineering projects. I enjoyed writing it and hope to write more when I come with additional ideas.

An excerpt from his article:

"Users of battery-operated applications desire the longest run time possible, and reducing the power loss can directly improve run time. Today it is well known that using a synchronous rectifier can reduce power loss and improve thermal capability. Designers of buck converters and controllers for stepdown applications are already employing this technique. Synchronous boost controllers also have been developed to address power efficiency in step-up applications.

Two typical boost applications can be used to demonstrate the difference between synchronous and nonsynchronous rectification. The first is a lower-input-voltage application that may operate at low duty cycles or, in other words, when the output voltage is close to the input voltage.  Example inputs for this system are a USB port or a lithium-ion (Li-Ion) battery pack with two or three series cells. The DC/DC power supply steps up the voltage for charging a two-cell Li-Ion battery or the battery of a tablet PC. The other application boosts the voltage of a system power rail to a high output voltage that can operate at higher duty cycles where the output voltage is much higher than the input voltage. An example input is a 12-V power rail. The high output voltage may be needed for power amplifiers, industrial PCs, or pump-and-dump energy storage for higher energy density."