10.1 Layout Guidelines

The LM5007 regulation and overvoltage comparators are very fast, and as such respond to short-duration noise pulses. Layout considerations are therefore critical for optimum performance:

1. Minimize the area of the high di/dt switching current loop consisting of the VIN and SW pins, freewheeling power diode, and input ceramic capacitor. Keep the input capacitor(s) close to the VIN pin of the LM5007. Place the cathode of the freewheeling diode close to the SW pin and and its anode near the return terminal of the input capacitor as illustrated in Figure 10. Route a short, direct connection to the RTN pin using polygon copper pours under the IC.
2. Place the inductor close to the SW pin of the LM5007. Minimize SW node copper area to reduce radiated noise related to high dv/dt.
3. Locate C_BST, R_CL, R_ON and C_VCC components as physically close as possible to their respective pins, thereby minimizing noise pickup in the printed-circuit tracks.
4. Locate the VOUT sense trace away from noise sources such as inductors. Place both feedback resistors close to the FB pin to minimize the length of the FB trace.
5. Place a solid GND plane on layer 2 of the PCB.

If the internal dissipation of the LM5007 converter produces excessive junction temperatures during normal operation, optimal use of the PCB ground plane can help considerably to dissipate heat. The exposed pad on the bottom of the WSON-8 package can be soldered to a ground plane on the PCB, and that plane should extend out from beneath the IC to help dissipate the heat. Additionally, the use of wide PCB traces for power connection can also help conduct heat away from the IC. Judicious positioning of the LM5007 converter within the end product, along with use of any available air flow (forced or natural convection), can help reduce the operating junction temperature.