The switching node rise and fall times
should be minimized for lowest switching loss. Proper layout of the components to
minimize high frequency current path loop (see Figure 11-1) is important to prevent electrical and magnetic field radiation and high
frequency resonant problems. Follow this specific order carefully to achieve the
proper layout.
- For lowest switching noise during forward/charge mode, place the
decoupling capacitor CPMID1 and then bulk capacitor CPMID2 positive terminals as
close as possible to PMID pin. Place the capacitor ground terminal close to the
GND pin using the shortest copper trace connection or GND plane on the same
layer as the IC. See Figure 11-2.
- For lowest switching noise during
reverse/OTG mode, place the CSYS1 and CSYS2 output capacitors' positive
terminals near the SYS pin. The capacitors' ground terminals must be via'd down
through multiple vias to an all ground internal layer that returns to IC GND pin
through multiple vias under the IC. See Figure 11-2.
- Since REGN powers the internal gate drivers, place the CREGN
capacitor positive terminal close to REGN pin to minimize switching noise. The
capacitor's ground terminal must be via'd down through multiple vias to an all
ground internal layer that returns to IC GND pin through multiple vias under the
IC. See Figure 11-2.
- Place the CVBUS and CBAT capacitors positive terminals as close
to the VBUS and BAT pins as possible. The capacitors' ground terminals must be
via'd down through multiple vias to an all ground internal layer that returns to
IC GND pin through multiple vias under the IC. See Figure 11-2.
- Place the inductor input pin near
the positive terminal of the SYS pin capacitors. Due to the PMID capacitor
placement requirements, the inductor's switching node terminal must be via'd
down with multiple via's to a second internal layer with a wide trace that
returns to the SW pin with multiple vias. See Figure 11-3. Using multiple vias ensures that the via's additional
resistance is negligible compared to the inductor's dc resistance and therefore
does not impact efficiency. The vias additional series inductance is negligible
compared to the inductor's inductance.
- Place the BTST capacitor on the
opposite side from the IC using vias to connect to the BTST pin and SW node. See
Figure 11-4.
- A separate analog GND plane for non-power related resistors and
capacitors is not required if those components are placed away from the power
components traces and planes.
- Ensure that the I2C SDA and SCL lines are routed away from the SW node.
Additionally, it is important that the
PCB footprint and solder mask for the BQ25622E cover the entire
length of each of the pins. GND, SW, PMID, SYS and BAT pins extend further into the
package than the other pins. Using the entire length of these pins reduces parasitic
resistance and increases thermal conductivity from the package into the board.