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
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 or capacitors as close as possible to the VIN and PGND pins of the device. This placement is the most critical component placement. 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 directly avoiding vias. Minimize the length of the connection from the inductor to the output capacitor.
- Connect the VO pin directly to the first output capacitor, COUT.
- Connect sensitive traces, such as the connections to the NR/SS, VO, and FB pins with short traces and be routed away from any noise source, such as the SW pin.
- Connect the PSNS pin directly to the system GND plane with a via.
- Place the second L-C filter, Lf and Cf, near the load to reduce any radiated coupling around the second L-C filter
- Avoid placing the ferrite bead in the keep out region as shown in Figure 7-3
- 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.
- See the recommended layout implemented on the EVM
and shown in the EVM user's guide, TPS62916EVM Evaluation
Module, as well as in Figure 7-3.