In industrial applications, it is very important to have robust and reliable packages that can withstand harsh environments as well as extreme electrical conditions. With the evolution and miniaturization of the integrated circuit, packages have also evolved and become smaller. Smaller packages lead to smaller total solutions, but also come with some disadvantages: It can be difficult to quickly and easily rework boards that fail in the field, and difficult to extract heat from the system.
In many industrial applications, total solution size is not as important as it is in the personal electronics space, so it’s better to use more rugged and robust packages that can be easily worked on, with superior heat-extraction capability to extend the life of industrial end equipment.
Integrated circuits come in a variety of shapes and sizes, with a variety of ways to physically connect them into a given circuit. In this post, I’ll discuss the package robustness of TI’s LM257x, LM258x, LM259x and LM267x SIMPLE SWITCHER® step-down regulators and more specifically, how these packages provide the easiest assembly compared to similar parts, along with superior thermal characteristics and moisture sensitivity. The TO-263 package is rated at moisture sensitivity level (MSL) 3, with a peak reflow temperature of 245°C. Plus, these parts have been around for decades, which is a testament to their longevity.
Ease of use
LM257x, LM258x, LM259x and LM267x nonsynchronous buck converters require only input and output capacitors, a power inductor, and a catch diode for a complete circuit application. Requiring only a few components for the complete circuit application makes each design very simple, with low part count and low cost. Figure 1 illustrates the products with each package option.
Figure 1: LM257x, LM258x, LM259x and LM267x SIMPLE SWITCHER regulators
The long leads of the DDPAK and TO packages allow for easy soldering during assembly compared to other packages that have very short leads or leads under the package. Also, TO-220 packages enable you to either bolt the device to the PCB and/or bolting an additional heat sink on the device, which can be useful depending on the application. For example, if an application requires extreme mechanical stability due to quick, sudden changes in direction or movement, it might be best to bolt the part to the board. Or if an application requires maximum heat dissipation, you can bolt multiple heat sinks to the device.
A smaller pitch means less distance between individual pins, making it more difficult for designers to route traces and assemble the board. So with the LM257x, LM258x, LM259x and LM267x, the pads are large and have larger pitch than many other packages (such as any from the small-outline package [SOP] family), enabling easy PCB layout even before assembly.
LM257x, LM258x, LM259x and LM267x devices have superior thermal resistance specifications due to their package size and type, which has excellent heat-dissipating characteristics. For both the TO-263 and TO-220 packages, the junction-to-case temperature increases 2°C/W, which beats most other parts with other packages. For example, the junction-to-case temperature increases 30°C/W for switching-regulator devices with smaller TSSOPs.
Better thermal resistance essentially means that the part won’t heat up as much during operation, which makes it (and thus the overall system) more stable and reliable. As the part heats up, the electrical characteristics can vary depending on how hot it gets. At higher temperatures, efficiency and regulation can become worse. If a part gets to its upper temperature threshold, it can become damaged, causing the system to fail.
The LM257x, LM258x, LM259x and LM267x have excellent thermal resistance among comparable parts, making them the best option in high-temperature or temperature-sensitive applications. In nearly all applications, a heat sink is not required. This is beneficial because it can save space and reduce cost and part count. See the data sheets of each device for more thermal information.
TI’s easy-to-use SIMPLE SWITCHER LM257x, LM258x, LM259x and LM267x regulator packages offer excellent thermal performance. Consider the regulators for your next design - they’ll provide a powerful punch for years to come.
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