8.9 PCB Layout Information

Good printed circuit board layout techniques are important to any switching circuitry, and switch mode power supplies are no different. When wiring the switching high-current paths, short and wide traces must be used. Therefore, it is important that the input and output capacitors be placed as close as possible to the MCP16367/8/9 to minimize the loop area.

The feedback resistors and feedback signal must be routed away from the switching node and the switching current loop. When possible, use ground planes and traces to shield the feedback signal and minimize noise and magnetic interference.

A robust MCP16367/8/9 layout begins with the placement of the input capacitor C_IN, which supplies current to the circuit input when the switch is on. In addition to providing high-frequency current, C_IN ensures a stable voltage source for the internal circuitry of the MCP16367/8/9. Excessive transients or ringing on the VIN pin can lead to unstable PWM operation, so minimizing these effects is important. Incorporating a ground plane on the bottom of the board ensures a low-resistance, low-inductance path for return current. The next priority is the placement of the freewheeling current loop, formed by the Schottky Diode, C_OUT and L. It is advisable to place the C_OUT return close to the C_IN return. The bootstrap capacitor must be placed between the boost pin and the switch node pin (SW). Additionally, R_TOP and R_BOT should be routed away from the switch node to prevent noise from coupling into the high-impedance FB input.