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 TPSM8291x demands careful attention to ensure 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 technical
brief for a detailed discussion of general best practices. Specific
recommendations for the device are listed below.
- The TPSM8291x has an integrated input capacitor. However, placement of the input capacitors must be placed as close as possible to the VIN and PGND pins of the device. Route the input capacitors directly to the VIN and PGND pins avoiding vias.
- Place the output capacitor ground close to the PGND pin and route it directly avoiding vias.
- Sensitive traces, such as the connections to the NR/SS and FB pins must be connected with short traces and be routed away from any noise source.
- Connect the PSNS pin directly to the system GND plane with a via.
- The SW pin must not be connected and must be left
floating. If the pin is soldered to PCB copper, the pour needs to be as small as
possible with no inner layer connections. The pin is provided for probing the
internal SW only, and not to be connected to any external component, as shown on
the EVM.
- Place the second L-C filter, Lf and Cf, near the load to reduce any radiated coupling around the second L-C filter
- Place the FB resistors, R1 and R2, close to the FB pin and route the VOUT connection from R1 to the load as a remote sense trace. If a second L-C filter is used, this connection must be made after Lf.
- The recommended layout is implemented on the EVM
and shown in the EVM user's guide.