10.1 Layout Guidelines

1. Keep the input switching current loop as small as possible.
2. Keep the SW node as physically small and short as possible to minimize parasitic capacitance and inductance and to minimize radiated emissions. Kelvin connections must be brought from the output to the feedback pin of the device.
3. Keep analog and non-switching components away from switching components.
4. Make a single point connection from the signal ground to power ground.
5. Do not allow switching current to flow under the device.
6. Keep the pattern lines for VIN and PGND broad.
7. Exposed pad of device must be connected to PGND with solder (DDA package only).
8. VREG5 capacitor must be placed near the device, and connected PGND.
9. Output capacitor must be connected to a broad pattern of the PGND.
10. Voltage feedback loop must be as short as possible, and preferably with ground shield.
11. Lower resistor of the voltage divider, which is connected to the VFB pin, must be tied to SGND.
12. Providing sufficient via is preferable for VIN, SW and PGND connection.
13. PCB pattern for VIN, SW, and PGND must be as broad as possible.
14. VIN capacitor mus be placed as near as possible to the device.

10.2 Layout Examples

Figure 19. PCB Layout

Figure 20. DRC Package PCB Layout

10.3 Thermal Considerations

This 8-pin DDA package incorporates an exposed thermal pad that is designed to be directly to an external heartsick. The thermal pad must be soldered directly to the printed-circuit board (PCB). After soldering, the PCB can be used as a heartsick. In addition, through the use of thermal vias, the thermal pad can be attached directly to the appropriate copper plane shown in the electrical schematic for the device, or alternatively, can be attached to a special heartsick structure designed into the PCB. This design optimizes the heat transfer from the integrated circuit (IC).

For additional information on the exposed thermal pad and how to use the advantage of its heat dissipating abilities, see PowerPAD™ Thermally Enhanced Package (SLMA002) and PowerPAD™ Made Easy (SMLA004).

Figure 21 shows the exposed thermal pad dimensions for this package.

Figure 21. Thermal Pad Dimensions