A proper layout is critical for the operation of any switched mode power supply, especially at high switching frequencies. Therefore, the PCB layout of the TPSM82851x demands careful attention to make sure of best performance. A poor layout can lead to issues like bad line and load regulation, instability, increased EMI radiation, and noise sensitivity. Refer to the Five Steps to a Great PCB Layout for a Step-Down Converter analog design journal for a detailed discussion of general best practices. Specific recommendations for the device are listed below.

• Place the input capacitor as close as possible to the VIN and GND pins of the device. This placement is the most critical component placement. Route the input capacitor directly to the VIN and GND pins avoiding vias.
• Place the output capacitor ground close to the VOUT and GND pins and route directly avoiding vias.
• Place the FB resistors, R1 and R2, and the feedforward capacitor C_FF close to the FB pin and place C_SS close to the SS/TR pin to minimize noise pickup.
• The recommended layout is implemented on the EVM and shown in TPSM82851xEVM Evaluation Module EVM user's guide and in Layout Example.
• See the recommended land pattern for the TPSM82851x at the end of this data sheet. For best manufacturing results, create the pads as solder mask defined (SMD), when some pins (such as VIN, VOUT, and GND) are connected to large copper planes. Using SMD pads keeps each pad the same size and avoids solder pulling the device during reflow.