Certain points must be considered before starting a layout work using the TPS53355.
- The power components (including input/output capacitors, inductor and TPS53355) must be placed on one side of the PCB (solder side). At least one inner plane should be inserted, connected to ground, in order to shield and isolate the small signal traces from noisy power lines.
- All sensitive analog traces and components such as VFB, PGOOD, TRIP, MODE and RF should be placed away from high-voltage switching nodes such as LL, VBST to avoid coupling. Use internal layer(s) as ground plane(s) and shield feedback trace from power traces and components.
- Place the VIN decoupling capacitors as close to the VIN and PGND pins as possible to minimize the input AC current loop.
- Because the TPS53355 controls output voltage referring to voltage across VOUT capacitor, the top-side resistor of the voltage divider should be connected to the positive node of the VOUT capacitor. Connect the GND of the bottom side resistor to the GND pad of the device. The trace from these resistors to the VFB pin should be short and thin.
- Place the frequency setting resistor (RF), OCP setting resistor (RTRIP) and mode setting resistor (RMODE) as close to the device as possible. Use the common GND via to connect them to GND plane if applicable.
- Place the VDD and VREG decoupling capacitors as close as possible to the device. Make sure GND vias are provided for each decoupling capacitor and make the loop as small as possible.
- The PCB trace defined as switch node, which connects the LL pins and high-voltage side of the inductor, should be as short and wide as possible.
- Connect the ripple injection VOUT signal (VOUT side of the C1 capacitor in Figure 8-2) from the terminal of ceramic output capacitor. The AC coupling capacitor (C2 in Figure 8-2) should be placed near the device, and R7 and C1 can be placed near the power stage.
- Use separate vias or trace to connect LL node to snubber, boot strap capacitor and ripple injection resistor. Do not combine these connections.