The board layout of any DC/DC switching converter is critical for the optimal performance of the design. Bad PCB layout design can disrupt the operation of an otherwise good schematic design. Even if the regulator still converts the voltage properly, the board layout can mean the difference between passing or failing EMI regulations. In a Buck converter, the most critical board layout path is between the input capacitor ground terminal and the synchronous rectifier ground. The loop formed by the input capacitor and the power FETs is a path for the high di/dt switching current during each switching period. This loop must always be kept as short as possible when laying out a board for any buck converter.

The LMZ10501 integrates the inductor and simplifies the DC/DC converter board layout. Refer to the example layout in Figure 8-26. There are a few basic requirements to achieve a good LMZ10501 layout.

1. Place the input capacitor C_IN as close as possible to the V_IN and PGND pins. V_IN (pin 7) and PGND (pin 6) on the LMZ10501 are next to each other which makes the input capacitor placement simple.

2. Place the V_CON filter capacitor C_VC and the R_B R_T resistive divider as close as possible to the V_CON and SGND pins. The C_VC capacitor (not R_B) must be the component closer to the V_CON pin, as shown in Figure 8-26. This allows for better bypass of the control voltage set at V_CON.

3. Run the feedback trace (from V_OUT to FB) away from noise sources.

4. Connect SGND to a quiet GND plane.

5. Provide enough PCB area for proper heat sinking. Refer to the Electrical Characteristics table for example θ_JA values for different board areas. Also, refer to AN-2020 for additional thermal design hints.

Refer to the evaluation board user's guide LMZ10501SIL and LMZ10500SIL SIMPLE SWITCHER® Nano Module Evaluation Board for a complete board layout example.