ZHCSJY0B June 2012 – June 2019 LMR12015 , LMR12020
PRODUCTION DATA.
The diagram of Figure 43 is also useful for analyzing the flow of continuous current vs. the flow of pulsating currents. The circuit paths with current flow during both the on-time and off-time are considered to be continuous current, while those that carry current during the on-time or off-time only are pulsating currents. Preference in routing should be given to the pulsating current paths, as these are the portions of the circuit most likely to emit EMI. The ground plane of a PCB is a conductor and return path, and it is susceptible to noise injection just like any other circuit path. The path between the input source and the input capacitor and the path between the catch diode and the load are examples of continuous current paths. In contrast, the path between the catch diode and the input capacitor carries a large pulsating current. This path should be routed with a short, thick shape, preferably on the component side of the PCB. Multiple vias in parallel should be used right at the pad of the input capacitor to connect the component side shapes to the ground plane. A second pulsating current loop that is often ignored is the gate drive loop formed by the SW and BOOST pins and boost capacitor CBOOST. To minimize this loop and the EMI it generates, keep CBOOST close to the SW and BOOST pins.