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 loop (see Figure 12-1) is important to prevent electrical and magnetic field radiation and high frequency resonant problems. Follow this specific order carefully to achieve the proper layout.
- Place input capacitor as close as possible to PMID pin and GND pin connections and use shortest copper trace connection or GND plane.
- Place inductor input pin to SW pin as close 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. Minimize parasitic capacitance from this area to any other trace or plane.
- Put output capacitor near to the inductor and the device. Ground connections need to be tied to the IC ground with a short copper trace connection or GND plane.
- Route analog ground separately from power ground. Connect analog ground and connect power ground separately. Connect analog ground and power ground together using thermal pad as the single ground connection point. Or using a 0-Ω resistor to tie analog ground to power ground.
- Use single ground connection to tie charger power ground to charger analog ground. Just beneath the device. Use ground copper pour but avoid power pins to reduce inductive and capacitive noise coupling.
- Place decoupling capacitors next to the IC pins and make trace connection as short as possible.
- It is critical that the exposed thermal pad on the backside of the device package be soldered to the PCB ground. Ensure that there are sufficient thermal vias directly under the IC, connecting to the ground plane on the other layers.
- Ensure that the number and sizes of vias allow enough copper for a given current path.
Refer to the BQ25601 and BQ25601D (PWR877) Evaluation Module User's Guide for the recommended component placement with trace and via locations. For the VQFN information, refer to the Quad Flatpack No-Lead Logic Packages Application Report and QFN and SON PCB Attachment Application Report.