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 TPSM8281x 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 CFF close to the FB pin and place CSS close to the SS/TR pin to minimize noise pickup.
- Place the RCF resistor close to the COMP/FSET pin to minimize the parasitic capacitance.
- Note that the recommended layout is implemented
on the EVM and shown in the TPSM8281xEVM-089 Evaluation
Module EVM user's guide, MagPack?
Technology 3A/6A Power Module with Frequency Sync Evaluation
Module EVM user's guide, and in Layout
Example.
- Note that the recommended land pattern for the TPSM8281x is shown 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.