11.1 Layout Guidelines

The VIN pin should be bypassed to ground with a low-ESR ceramic bypass capacitor. Care should be taken to minimize the loop area formed by the bypass capacitor connections, the VIN pin, and the anode of the catch diode. The typical recommended bypass capacitance is 10-μF ceramic with a X5R or X7R dielectric and the optimum placement is closest to the VIN pins and the source of the anode of the catch diode. Figure 24 shows a PCB layout example. The GND pin should be tied to the PCB ground plane at the pin of the IC. The source of the low-side MOSFET should be connected directly to the top side PCB ground area used to tie together the ground sides of the input and output capacitors as well as the anode of the catch diode. The PH pin should be routed to the cathode of the catch diode and to the output inductor. Because the PH connection is the switching node, the catch diode and output inductor should be located very close to the PH pins, and the area of the PCB conductor minimized to prevent excessive capacitive coupling. For operation at full rated load, the top-side ground area must provide adequate heat dissipating area. The TPS54231 device uses a fused lead frame so that the GND pin acts as a conductive path for heat dissipation from the die. Many applications have larger areas of internal or back-side ground plane available, and the top-side ground area can be connected to these areas using multiple vias under or adjacent to the device to help dissipate heat. The additional external components can be placed approximately as shown. Obtain acceptable performance with alternate layout schemes may be possible, however this layout has been shown to produce good results and is intended as a guideline.

11.2 Layout Example

Figure 24. TPS54231 device Board Layout

11.3 Estimated Circuit Area

The estimated printed circuit board area for the components used in the design of Figure 10 is 0.68 in². This area does not include test points or connectors.

11.4 Electromagnetic Interference (EMI) Considerations

As EMI becomes a rising concern in more and more applications, the internal design of the TPS54231 device takes measures to reduce the EMI. The high-side MOSFET gate drive is designed to reduce the PH pin voltage ringing. The internal IC rails are isolated to decrease the noise sensitivity. A package bond wire scheme is used to lower the parasitics effects.

To achieve the best EMI performance, external component selection and board layout are equally important. Follow the steps listed in the Detailed Design Procedure section to prevent potential EMI issues.