10.1 Layout Guideline
The PCB layout is a very important step in the power supply design. Following points should be considered.
- Place red marked components first and as close as possible to the device, keep red lines short.
- The bolder the line the wider the trace should be on the PCB because bold lines carry high currents.
- The input capacitors for INBK1, INBK3 and INVL should be placed as close as possible to the IC.
- For V(AVDD) the line SW, Diode, SWI as well as the connection PGND to SWI capacitor should be kept short and low resistive.
- The compensation network for the Boost converter V(AVDD) must be placed as close as possible to the IC and connected by short lines to COMP and AGND to avoid noise coupling.
- For V(IO) the line SWBK1, Diode, GND of INBK1 capacitor should be kept short and low resistive.
- For V(CORE) an additional input capacitor should be used when the V(IO) output capacitor line is longer than 1 cm or a wide connection line is not possible to stabilize the input voltage.
- Feedback lines starting at the output capacitors should be routed through a non noisy area away from switching traces. If possible the feedback lines should be kept short to reduce noise coupling.
- Inductors can be placed further away from the IC to avoid IC heating through the inductor.
- All IC Grounds (AGND, PGNDx) must be connected to the Exposed Thermal PAD.
- Avoid vias in Power lines when possible because of their high inductance and resistance.
- The Exposed Thermal PAD of the QFN package must be soldered to a big GND cooling area. For good thermal conduction to the cooling area as much as possible vias should be used to keep the device cool.
- The thermal resistor NTC should be placed away from heat sources. For most accurate environment temperature measurement the NTC must be placed at the coldest point of the PCB.