As for all switching power supplies, especially
those running at high switching frequency and high currents, layout is an important design
step. If layout is not carefully done, the regulator can suffer from instability and noise
problems.
- Place the 0.1-μF small package (0402)
ceramic capacitors close to the VIN/VOUT pins to minimize high frequency current loops.
This improves the radiation of high-frequency noise (EMI) and efficiency.
- Use multiple GND vias near PGND pin to
connect the PGND to the internal ground plane. This also improves thermal
performance.
- Minimize the SW1 and SW2 loop areas as
these are high dv/dt nodes. Use a ground plane under the switching regulator to minimize
interplane coupling.
- Use Kelvin connections to
RSENSE for the current sense signals ISP and ISN and run lines in parallel
from the RSENSE terminals to the IC pins. Place the filter capacitor for the
current sense signal as close to the IC pins as possible.
- Place the BOOT1 bootstrap capacitor
close to the IC and connect directly to the BOOT1 to SW1 pins. Place the BOOT2 bootstrap
capacitor close to the IC and connect directly to the BOOT2 and SW2 pins.
- Place the VCC capacitor close to the IC
with wide and short trace. The GND terminal of the VCC capacitor should be directly
connected with PGND plane through three to four vias.
- Isolate the power ground from the
analog ground. The PGND plane and AGND plane are connected at the terminal of the VCC
capacitor. Thus the noise caused by the MOSFET driver and parasitic inductance does not
interface with the AGND and internal control circuit.
- Place the compensation components as
close to the COMP pin as possible. Keep the compensation components, feedback
components, and other sensitive analog circuitry far away from the power components,
switching nodes SW1 and SW2, and high-current trace to prevent noise coupling into the
analog signals.
- To improve thermal performance, it is
recommended to use thermal vias beneath the TPS55287 connecting the VIN pin to a large
VIN area, and the VOUT pin to a large VOUT area separately.