13.1 Layout Guidelines

For all switching power supplies, the layout is an important step in the design, especially at high peak currents and high switching frequencies. If the layout is not carefully done, the regulator could show stability problems as well as EMI problems. Therefore, use wide and short traces for the main current path and for the power ground tracks. The input capacitor, output capacitor, and the inductor should be placed as close as possible to the IC. Use a common ground node for power ground and a different one for control ground to minimize the effects of ground noise. Connect these ground nodes at any place close to one of the ground pins of the IC.

The feedback divider should be placed close to the IC to keep the feedback connection short. To lay out the ground, short and wide traces are recommended. This avoids ground shift problems, which can occur due to superimposition of power ground current onto the feedback divider. Figure 15 shows the recommended board layout.

13.2 Layout Example

Figure 15. Suggested Layout

13.3 Thermal Considerations

The implementation of integrated circuits in low-profile and fine-pitch surface-mount packages typically requires special attention to power dissipation. Many system-dependent issues such as thermal coupling, airflow, added heat sinks and convection surfaces, and the presence of other heat-generating components affect the power-dissipation limits of a given component.

Three basic approaches for enhancing thermal performance are listed below:

• Improving the power dissipation capability of the PCB design
  • For example, increase of the GND plane on the top layer which is connected to the exposed thermal pad
  • Use thicker copper layer
• Improving the thermal coupling of the component to the PCB
• Introducing airflow in the system

Junction-to-ambient thermal resistance is highly application and board-layout dependent. In applications where high maximum power dissipation exists, special care must be paid to thermal dissipation issues in board design. The maximum junction temperature (T_J) of the TPS61252 is 150°C.