11.1 Layout Guidelines

As 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 must 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.

To lay out the control ground, TI recommends using short traces as well, separated from the power ground traces. This avoids ground shift problems, which can occur due to superimposition of power ground current and control ground current.

11.2 Layout Example

Figure 107. Suggested Layout (Top)

11.3 Thermal Considerations

Implementation of integrated circuits in low-profile and fine-pitch surface-mount packages typically requires special attention to power dissipation. Many system-dependant 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
• 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 TPS6130xx is 150°C.

The maximum power dissipation is especially critical when the device operates in the linear down mode at high LED current. For single pulse power thermal analysis (for example, flashlight strobe), the allowable power dissipation for the device is given by Figure 108. These values are derived using the reference design.

Figure 108. Single Pulse Power Capability