10.1 Layout Guidelines

To improve ac performance such as PSRR, output noise, and transient response, the board is recommended to be designed with separate ground planes for IN and OUT, with each ground plane connected only at the GND pin of the device. This grounding scheme is commonly referred to as star grounding. In addition, directly connect the ground connection for the output capacitor to the GND pin of the device.

Equivalent series inductance (ESL) and ESR must be minimized in order to maximize performance and ensure stability. Every capacitor must be placed as close as possible to the device and on the same side of the PCB as the regulator itself.

Do not place any of the capacitors on the opposite side of the PCB from where the regulator is installed. The use of vias and long traces is strongly discouraged because they can impact system performance negatively and even cause instability.

If possible, and to ensure the maximum performance denoted in this document, use the same layout pattern used for the TPS7A16A-Q1 evaluation board, available at www.ti.com.

Layout is a critical part of good power-supply design. There are several signal paths that conduct fast-changing currents or voltages that can interact with stray inductance or parasitic capacitance to generate noise or degrade the power-supply performance. To help eliminate these problems, bypass the IN pin to ground with a low-ESR ceramic bypass capacitor with X5R or X7R dielectric.

Acceptable performance can be obtained with alternative PCB layouts; however, the layout and the schematic have been shown to produce good results and are meant as a guideline.

Figure 19 illustrates the schematic for the suggested layout. Figure 20 and Figure 21 depict the top and bottom printed circuit board (PCB) layers for the suggested layout, respectively.