11.1 Layout Guidelines

As for all switching power supplies, especially those switching at high frequencies and/or providing high currents, layout is an important design step. If layout is not carefully done, the regulator could suffer from instability as well as noise problems. To maximize efficiency, switch rise and fall times should be as short as possible. To reduce radiation of high-frequency switching noise and harmonics, proper layout of the high-frequency switching path is essential. Minimize the length and area of all traces connected to the SW pin and always use a ground plane under the switching regulator to minimize interplane coupling. The high current path including the switch, Schottky diode, and output capacitor, contains nanosecond rise and fall times and should be kept as short as possible. The input capacitor needs not only to be close to the VIN pin, but also to the GND pin to reduce the IC supply ripple. Figure 20 shows a sample layout.

11.2 Layout Example

Figure 20. PCB Layout Recommendation

11.3 Thermal Considerations

The maximum IC junction temperature should be restricted to 125°C under normal operating conditions. This restriction limits the power dissipation of the TPS61170-Q1. Calculate the maximum allowable dissipation, P_D(max), and keep the actual dissipation less than or equal to P_D(max). The maximum-power-dissipation limit is determined using Equation 14:

Equation 14.

where

• T_A is the maximum ambient temperature for the application.
• R_θJA is the thermal resistance junction-to-ambient given in the Thermal Information table.

The TPS61170-Q1 comes in a thermally enhanced SON package. This package includes a thermal pad that improves the thermal capabilities of the package. The R_θJA of the SON package greatly depends on the PCB layout and thermal pad connection. The thermal pad must be soldered to the analog ground on the PCB. Using thermal vias underneath the thermal pad as illustrated in the layout example. Also see the QFN/SON PCB Attachment application report (SLUA271).