A multi-function pinout is when two or more features are integrated into one pin. A table found in the device’s data sheet is used to decipher what features are available with guidance of how to select the desired combination. Table 1-1 is an example of the mode pin selection of TPS563211 data sheet. There are two feature selections with a total of four combinations. A resistor value (in the range of acceptable values) strapped from ground to the mode pin is used to select both feature operations. Not all multi-function pins cover the same features, some are bifunctional, either-or, while others, such as mode or S-config pins, cover 2, 3, 4+ features in just one pin, exemplified in Table 1-2.
|Recommended Mode Resistor Value||Operation Mode in Light Mode||Function of PG/SS Pin|
|[0, 12] kΩ||0||Eco-mode||Power Good|
|[30, 50] kΩ||47 kΩ||Eco-mode||Soft Start|
|[83, 120] kΩ||100 kΩ||FCCM||Soft Start|
|[180, ∞] kΩ||Float||FCCM||Power Good|
Since multi-function pins combine what used to be individual pins into one, the resulting smaller package has less pins that need to be configured. Less pins mean less time researching to find the right passive, less time calculating to find the right values, and less time placing each component in a layout. The more features a single pin incorporates, the better the flexibility to design time ratio.
The ability to reuse a design for various projects with minimal alteration saves time and development cost. Multi-functional pins are ideal when it comes to this copy and paste methodology – a simple resistor change could be all that is needed from one project to another. In some cases, such as the TPS62903, multiple multi-function pins are used for additional flexibility shown in Figure 1-1 to cover very different applications with just one part, from space constrained smart locks needing low quiescent current, to data centers needing high efficiency.
Multi-function pins help simplify a design with fewer external components to configure the feature sets. Fewer passives needed to design-in a given part results in a smaller total solution size and cost. See the second reference in Additional Resources section. Using the same device on multiple projects and a smaller BOM count both contribute to drastically simplifying the supply chain.
Reducing package size is the driving factor behind the creation of multi-function pinouts, but there are many more benefits that they bring to the table. Using products that incorporate one or more multi-function pins can result in reduced solution size and BOM count, increased application flexibility, quicker time-to-market, and a simplified supply chain. All making life a little easier.