Regarding the layout of the driver circuit, as illustrated in Figure 3-5, when the IC enables the MOSFET, current flows from the VCC capacitor through the internal driver and gate resistor to charge the MOSFET's gate terminal. The return current flows from the MOSFET's source (PGND) through the circuit network back to the VCC capacitor's AGND. This current transient occurs within several nanoseconds with peak values reaching 2A. Consequently, judicious layout design that minimizes the current path length is of paramount importance to reduce loop inductance. Simultaneously, careful attention must be paid to the connection topology of PGND and AGND to ensure that the return current flows smoothly back to the VCC capacitor's AGND, avoiding excessive ground loops or multiple ground return paths. This prevents noise interference from ground potential differences, which could otherwise degrade the MOSFET's switching speed and efficiency as well as compromise the electromagnetic compatibility (EMC) of the entire circuit.

The boost circuit layout also imposes stringent requirements, as shown in Figure 3-7. The boost current does not flow through the IC's GND pin or thermal pad. To minimize the current path length, multilayer ceramic capacitors (MLCCs) should be placed as close as possible to the VOUT pin (within 1 mm). The low-side MOSFET Q1 must also be positioned as proximate as possible to the SW pin. Additionally, it is recommended to place relatively small-value output capacitors (100 nF – 1 μF, 0603 package) near the VOUT pin to bypass high-frequency noise.

Figure 3-8 presents test results demonstrating noise coupling into the chip, wherein PGND noise is capacitively coupled to the control ground (AGND) through the thermal pad, affecting the bandgap reference voltage and subsequently degrading IC performance. The layout-level solution is to connect the thermal pad directly to AGND, thereby eliminating the readily conductive noise coupling path between PGND and the control ground AGND through the thermal pad.