LTpowerCAD II: A Design Tool for Switching Regulators

The design of switching power supplies can be challenging and time consuming. Even for an experienced engineer, such aspects as proper loop compensation and load transit performance generally aren’t straightforward to estimate. LTpowerCAD streamlines this task for you. It guides you through the entire design process for you from power stage to feedback loop optimization to reduce your design time and effort. Learn more about how Analog Devices is powering the future.

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Hi, my name is Sam Young, and I'm an Applications Engineer for Power Products at Analog Devices' Power by Linear. Today, I'd like to introduce the LTpowerCAD design tool program as a powerful tool to help you design application circuits with Analog Devices' Power by Linear's micromodule and monolithic DC-DC regulator products.

Designing switching power supplies can often be challenging and time consuming, especially for a less-experienced engineer. But even for an experienced engineer, a time-intensive process of component value adjustment and reiteration of calculations is expected. Furthermore, even with the specifications and guidelines available in the data sheet, such aspects as proper loop compensation and low transient performance generally aren't straightforward to estimate.

LTpowerCAD design tool streamlines this task for you. It provides you with key performance estimations you need to optimize your design. This powerful tool guides you through the entire design process from power stage to feedback loop optimization to reduce your design time and effort.

LTpowerCAD is a Microsoft Excel based program with a user-friendly schematic interface. You can get a free download at Analog Devices' Power by Linear's website at It helps you select the proper LTC products for your application requirements, provides power stage component value recommendations with parameter warnings and performance calculations tailored to your supplier requirements.

Bench-verified loop gain and low transient performance estimates are also provided to complete your design. And at the end, the application circuit can be exploited for real-time simulation using Analog Devices' Power by Linear's LTspice Simulator.

In addition, the tool offers many design reference features including a built-in power component library, layout references, and a design summary to detail the total cost, solution size, and a stress analysis of your final design. Let's step into a quick example to see the LTpowerCAD Tool's design flow and some of the main features this powerful tool has to offer. In this example, we need a supply to support an output voltage of 1.5 volts at 10 amps from a 12 volt nominal input.

For this popular application, we see there are quite a few parts to choose from. Let's choose a controller type part and go with the LTC3851A buck regulator. All of our desired parameters entered are automatically input into our design. These values are still adjustable by rewriting the values in the blue cells.

Yellow cells hold reference in calculated values specific to the part. LTpowerCAD is arranged with the user-friendly schematic interface. Yellow cells hold calculated values based on our parameter and component selections. Blue cells allow you to adjust your component selections. In this example, the design tool has already calculated your input RMS current, inductor ripple current, output ripple voltage, feedback voltage setting resistor, etcetera.

If an undesired value is entered, red warnings appear to indicate warnings of improper component values. So you can determine if these satisfy your application requirements and ratings of any external components you plan to use. For example, if your output voltage ripple requirements are not yet met, you can modify your design parameters appropriately at any time.

For your later reference, click view layout example to see a recommended power section layout for your PCB's top layer. On the Loss Estimate and Breakdown tab, the program estimates the efficiency and loss breakdown for the various loss sources of your design.

Each component library includes a wide range of built-in components. The library is updatable for the user to add their own components. Links are also available in the library to visit the part search or information pages of popular component vendors. The loss estimate tabincludes efficiency and power loss curves versus load current as well as a chart showing a breakdown of the various losses in the system.

LTpowerCAD also estimates your loop gain to help determine loop and load transient performances.

Operating conditions and compensation component value inputs are adjustable with real-time results, allowing you to fine-tune your design. Besides the loop gain plot, a selection of frequency and impedance plots are also available to see the contribution of the different stages of the loop.

When you're satisfied with your initial design, you can look into its operation in more detail by exporting to run a real-time simulation of the circuit in LTspice. Of course, bench verification is indispensable for taking into account all factors of your design. As we have seen, LTpowerCAD is a user-friendly and powerful tool in creating a good starting point for which to base your design.

It allows you to save time and effort in the first steps to completing your application with Analog Devices' Power by Linear's micromodule and monolithic DC-DC regulators. LTpowerCAD is a free download available from our website.


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