10.1 Layout Guidelines

Layout is a critical portion 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 performance.

• To reduce parasitic effects, the VIN terminal should be bypassed to ground with a low ESR ceramic bypass capacitor with X5R or X7R dielectric.
• Care should be taken to minimize the loop area formed by the bypass capacitor connections, the VIN terminal, and the anode of the catch diode.
• The GND terminal should be tied directly to the power pad under the IC and the PowerPAD™.
• The PowerPAD™ should be connected to internal PCB ground planes using multiple vias directly under the IC.
• The SW terminal should be routed to the cathode of the catch diode and to the output inductor.
• Since the SW connection is the switching node, the catch diode and output inductor should be located close to the SW terminals, and the area of the PCB conductor minimized to prevent excessive capacitive coupling.
• For operation at full rated load, the top side ground area must provide adequate heat dissipating area.
• The RT/CLK terminal is sensitive to noise so the RT resistor should be located as close as possible to the IC and routed with minimal lengths of trace.
• The additional external components can be placed approximately as shown.
• It may be possible to obtain acceptable performance with alternate PCB layouts, however this layout has been shown to produce good results and is meant as a guideline.

10.2 Layout Examples

Figure 58. PCB Layout Example