11.1.1 Layout Procedure
Place the power components first, with ground terminals adjacent to the low-side FET.
- Mount the controller IC as close as possible to the high and low-side MOSFETs. Make the grounds and high and low-sided drive gate drive lines as short and wide as possible. Place the series gate drive resistor as close to the MOSFET as possible to minimize gate ringing.
- Locate the gate drive components (D1 and C12) together and near the controller IC; refer to Figure 38. Be aware that peak gate drive currents can be as high as 4 A. Average current up to 75 mA can flow from the VCC pin to the VCC capacitor through the bootstrap diode to the bootstrap capacitor. Size the traces accordingly.
- Figure 39 shows the high-frequency loops of the synchronous buck converter. The high frequency current flows through Q1 and Q2, through the power ground plane and back to VIN through the ceramic capacitors C6, C7, and C8. This loop must be as small as possible to minimize EMI. Refer to Figure 41 and Figure 42 for the recommended PCB layout.
- Make the PGND and AGND connections to the LM25141-Q1 controller as shown in Figure 40. Create a power grounds directly connected to all high-power components and an analog ground plane for sensitive analog components. The analog ground plane (AGND) and power ground plane (PGND) must be connected at a single point directly under the IC (at the die attach pad or DAP).