When using the adjustable version, special care must be
taken as to the location of the feedback resistors and the
associated wiring. Physically locate both resistors near the
IC, and route the wiring away from the inductor, especially an
open core type of inductor.
Application Information (Continued)
Layout is very important in switching regulator designs. Rap-
idly switching currents associated with wiring inductance can
generate voltage transients which can cause problems. For
minimal inductance and ground loops, the wires indicated by
heavy lines (in Figure 2 and Figure 3) should be wide
printed circuit traces and should be kept as short as
possible. For best results, external components should be
located as close to the switcher IC as possible using ground
plane construction or single point grounding.
LLP Package Devices
The LM2674 is offered in the 16 lead LLP surface mount
package to allow for increased power dissipation compared
to the SO-8 and DIP.
The Die Attach Pad (DAP) can and should be connected to
PCB Ground plane/island. For CAD and assembly guide-
lines refer to Application Note AN-1187 at http://
power.national.com.
If open core inductors are used, special care must be
taken as to the location and positioning of this type of induc-
tor. Allowing the inductor flux to intersect sensitive feedback,
IC ground path, and COUT wiring can cause problems.
23
www.national.com
NSC [ National Semiconductor ]
