10.1 Layout Guidelines

The VIN pins are connected together on the printed board (PCB) and bypassed with a low-ESR ceramic bypass capacitor. Minimize the loop area formed by the bypass capacitor connections, the VIN pins, and the TPS54110 ground pins. The recommended bypass capacitor is 10-μF (minimum) ceramic with X5R or X7R dielectric. The optimum placement is closest to the VIN pins and the AGND and PGND pins. See Figure 30 for an example layout. It has an area of ground on the top layer directly under the IC, with an exposed area for connection to the PowerPAD. Use vias to connect this ground area to any internal ground planes. Use additional vias at the ground side of the input and output filter capacitors as well. Tie the AGND and PGND pins to the PCB ground area under the device as shown. Use a separate wide trace for the analog-ground path, connecting the voltage set-point divider, timing resistor RT, slow-start capacitor and bias-capacitor grounds. Tie the PH pins together and route to the output inductor. Since the PH connection is the switching node, locate the inductor very close to the PH pins, and minimize the area of the conductor to prevent excessive capacitive coupling. Connect the boot capacitor between the phase node and the BOOT pin as shown. Keep the boot capacitor close to the IC and minimize the conductor trace lengths. Connect the output-filter capacitor(s) as shown between the VOUT trace and PGND. It is important to keep the loop formed by the PH pins, L_OUT, C_OUT, and PGND as small as is practical. Place the compensation components from the VOUT trace to the VSENSE and COMP pins. Do not place these components too close to the PH trace. Due to the size of the IC package and the device pin-out, they must be somewhat closely routed while maintaining as much separation as possible, yet keeping the layout compact. Connect the bias capacitor from the VBIAS pin to analog ground using the isolated analog ground trace. If a slow-start capacitor or RT resistor is used, or if the SYNC pin is used to select 350-kHz operating frequency, connect them to this trace as well.