10.1 Layout Guidelines

Careful PCB design and layout are important in a high current, fast switching circuit (with high current and voltage slew rates) to assure appropriate device operation and design robustness. As expected, certain issues must be considered before designing a PCB layout using the LM27402. The main switching loop of the power stage is denoted by 1 in Figure 48. The buck converter topology means that particularly high di/dt current will flow in loop 1, and it becomes mandatory to reduce the parasitic inductance of this loop by minimizing its effective loop area. For loop 2 however, the di/dt through inductor L_F and capacitor C_OUT is naturally limited by the inductor. Keeping the area of loop 2 small is not nearly as important as that of loop 1. Also important are the gate drive loops of the low-side and high-side MOSFETs, denoted by 3 and 4, respectively, in Figure 48.

Figure 48. DC/Dc Converter Ground System With Power Stage and Gate Drive Circuit Switching Loops