With the proviso to locate the controller as close as possible to the power MOSFETs to minimize gate driver trace runs, the components related to the analog and feedback signals as well as current sensing are considered in the following:
- Separate power and signal traces, and use a ground plane to provide noise shielding.
- Place all sensitive analog traces and components
related to COMP, FB, ISNS+, and RT away from
high-voltage switching nodes such as SW, HO, LO,
or CBOOT to avoid mutual coupling. Use internal
layer or layers as ground plane or planes. Pay
particular attention to shielding the feedback
(FB) and current sense (ISNS+ and VOUT) traces
from power traces and components.
- Locate the upper and lower feedback resistors (if required) close to the FB pin, keeping the FB trace as short as possible. Route the trace from the upper feedback resistor to the required output voltage sense point at the load.
- Route the ISNS+ and VOUT sense traces as
differential pairs to minimize noise pickup and
use Kelvin connections to the applicable shunt
resistor (if shunt current sensing is used) or to
the sense capacitor (if inductor DCR current
sensing is used).
- Minimize the loop area from the VCC and VIN pins
through their respective decoupling capacitors to the PGND pin. Locate these
capacitors as close as possible to the LM5148.