10.1 Layout Guidelines

To achieve optimal electrical and thermal performance, an optimized PCB layout is required. Figure 20 and Figure 22 show typical, top-side PCB layouts. Some considerations for an optimized layout are:

• Use large copper areas for power planes (VIN, VOUT, and PGND) to minimize conduction loss and thermal stress.
• When adding input and output ceramic capacitors, place them close to the device pins to minimize high frequency noise.
• Locate any additional output capacitors between the ceramic capacitors and the load.
• Keep AGND and PGND separate from one another. The connection is made internal to the device.
• Place R_SET as close as possible to the VADJ pin.
• Use multiple vias to connect the power planes to internal layers.

10.2 Layout Examples

The layout shown in Figure 20 shows the minimum solution size with only a single voltage setting resistor (R1) as the only additional required component. Figure 21 shows a typical internal PCB layer with a trace connecting the VS+ pin to VOUT near the load.

Figure 20. Minimum Component Layout

Figure 21. VS+ Trace on Internal Layer

Figure 22 shows a layout with the placement of additional ceramic input capacitors (C1, C3) and ceramic output capacitors (C2, C4) for designs that require additional ripple reduction or improved transient response. Figure 23 shows a typical internal PCB layer with a trace connecting the VS+ pin to VOUT near the load

Figure 22. Layout with Optional CIN and COUT

Figure 23. VS+ Trace on Internal Layer

10.3 EMI

The TPSM84A21 is compliant with EN55022 Class B radiated emissions. Figure 24 to Figure 27 show typical examples of radiated emissions plots for the TPSM84A21. Graphs included show plots of the antenna in the horizontal and vertical positions.

Figure 24. Radiated Emissions 12-V Input, 0.8-V Output,
10-A Load, Horizontal Antenna

Figure 26. Radiated Emissions 12-V Input, 1.2-V Output,
10-A Load, Horizontal Antenna

Figure 25. Radiated Emissions 12-V Input, 0.8-V Output,
10-A Load, Vertical Antenna

Figure 27. Radiated Emissions 12-V Input, 1.2-V Output,
10-A Load, Vertical Antenna