The following list summarizes the essential guidelines for PCB layout and component placement to optimze DC/DC module performance, including thermals and EMI signature. Figure 11-1 and Figure 11-2 show a recommended PCB layout for the TPSM63606 with optimized placement and routing of the power-stage and small-signal components.

• Place input capacitors as close as possible to the VIN pins. Note the dual and symmetrical arrangement of the input capacitors based on the VIN1 and VIN2 pins located on each side of the module package. The high-frequency currents are split in two and effectively flow in opposing directions such that the related magnetic fields contributions cancel each other, leading to improved EMI performance.
  • Use low-ESR 1206 or 1210 ceramic capacitors with X7R or X7S dielectric. The module has integrated dual 0402 input capacitors for high-frequency bypass.
  • Ground return paths for the input capacitors should consist of localized top-side planes that connect to the PGND pads under the module.
  • Even though the VIN pins are connected internally, use a wide polygon plane on a lower PCB layer to connect these pins together and to the input supply.
• Place output capacitors as close as possible to the VOUT pins. A similar dual and symmetrical arrangement of the output capacitors enables magnetic field cancellation and EMI mitigation.
  • Ground return paths for the output capacitors should consist of localized top-side planes that connect to the PGND pads under the module.
  • Even though the VOUT pins are connected internally, use a wide polygon plane on a lower PCB layer to connect these pins together and to the load, thus reducing conduction loss and thermal stress.
• Keep the FB trace as short as possible by placing the feedback resistors close to the FB pin. Reduce noise sensitivity of the output voltage feedback path by placing the resistor divider close to the FB pin, rather than close to the load. FB is the input to the voltage-loop error anplifier and represents a high-impedance node sensitive to noise. Route a trace from the upper feedback resistor to the required point of output voltage regulation.
• Use a solid ground plane on the PCB layer directly below the top layer with the module. This plane acts as a noise shield by minimizing the magnetic fields associated with the currents in the switching loops. Connect AGND pins 6 and 11 directly to PGND pin 19 under the module.
• Provide enough PCB area for proper heatsinking. Use sufficient copper area to acheive a low thermal impedance commensurate with the maximum load current and ambient temperature conditions. Provide adequate heatsinking for the TPSM63606 to keep the junction temperature below 150°C. For operation at full rated load, the top-side ground plane is an important heat-dissipating area. Use an array of heat-sinking vias to connect the exposed pads (PGND) of the package to the PCB ground plane. If the PCB has multiple copper layers, connect these thermal vias to inner-layer ground planes. Make the top and bottom PCB layers preferably with two-ounce copper thickness (and no less than one ounce).