The basic PCB board layout requires a separation
of sensitive signal and power paths. If the layout is not carefully done, the
regulator can suffer from the instability or noise problems.
The following checklist is suggested that be
followed to get good performance for a well-designed board:
- Minimize the high current path from output of chip, the output capacitor
to the GND of chip. This loop contains high di / dt switching currents (nano
seconds per ampere) and easy to transduce the high frequency noise.
- Minimize the length and area of all traces connected to the SW pin, and
always use a ground plane under the switching regulator to minimize inter plane
coupling.
- Use a combination of bulk capacitors and smaller ceramic capacitors with
low series resistance for the input and output capacitors. Place the smaller
capacitors closer to the IC to provide a low impedance path for decoupling the
noise.
- The ground area near the IC must provide adequate heat dissipating area.
Connect the wide power bus (for example, VOUT, SW, GND ) to the large
area of copper, or to the bottom or internal layer ground plane, using vias for
enhanced thermal dissipation.
- Place the input capacitor being close to the VIN pin and the
PGND pin in order to reduce the input supply ripple.
- Place the noise sensitive network like the feedback and compensation
being far away from the SW trace.
- Use a separate ground trace to connect the feedback and the loop compensation circuitry. Connect this ground trace to the main power ground at a single point to minimize circulating currents.