This is an introduction for the sections on Power Supply and Layout.

There are multiple grounds and bias power pins for digital controllers such as the UCD3138 family products. They are separated from each other because of the digital circuitry and analog circuitry inside the device. Normally, digital circuits draw more current and generate more noise, but the digital signal is not sensitive to the noise; while the analog circuit needs quiet power and grounding. A deliberate grounding and power separation outside the controller can reduce the interference between analog circuits and digital circuits, and therefore, the controller can have better performance. When they are separated from each other, take care of how the analog circuit and digital circuit are grouped, respectively, and then how and where they are tied together. With improper grounding, the device performance can be negatively impacted including DPWM abnormal, device reset, ADC results, output voltage ripple, and so on.

These sections supersede all older guidelines on UCD family board design and layout. Older EVM designs may not meet all of these guidelines.

In the PCB design, there are two options. One is to have two separate grounds - digital ground and analog ground. The other is to use a single ground plane for both digital ground and analog ground. With two separate ground planes, how to connect digital ground and analog ground is very important, and the PCB must be designed very carefully. With a single ground plane, there is no concern regarding where two grounds are tied together, and it makes the PCB design easier. Here, TI recommends using a single ground plane.

In these sections, digital ground is denoted as DGND; analog ground is denoted as AGND; a single ground plane is denoted as SGND.