10.1 Layout Guidelines
The switching node rise and fall times should be minimized for minimum switching loss. Proper layout of the components to minimize high frequency current path loops is important to prevent electrical and magnetic field radiation and high-frequency resonant problems. Here is a PCB layout priority list for proper layout. Layout PCB according to this specific order is essential.
- Utilize at least four-layer board for optimal layout, and assign one layer as solid ground plane near the IC to minimize high-frequency current path
- Place flying capacitor as close to CLFY+ and CLFY– bumps as possible. Minimize the copper area of this trace to lower electrical and magnetic field radiation but make the trace wide enough to carry the charging current. Do not use multiple layers in parallel for this connection.
- Place input capacitor as close as possible to PMID bumps and PGND bumps and use solid GND plane underneath the IC. Use plenty of vias close to PMID capacitor GND terminal and IC PGND bumps to ensure low parasitic connection to GND plane.
- Place inductor input terminal as close to SW bumps as possible. Minimize the copper area of this trace to lower electrical and magnetic field radiation but make the trace wide enough to carry the charging current.
- Put output capacitor near to the inductor and the device. Ground connections need to be tied to the device ground with a short copper trace connection or GND plane.
- Decoupling capacitors should be placed next to the device and make trace connection as short as possible.
- Ensure that there are sufficient thermal vias directly under bumps of the power FETs, connecting to copper on other layers.
- The via size and number should be enough for a given current path.
- Route BATP and BATN away from switching nodes such as SW and CFLY+, CFLY–.
Refer to the EVM design and Figure 61 for the recommended component placement with trace and via locations.