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LM2854 PC Board Layout

8 LM2854 PC Board Layout

The demo board is based on a small 1.15” × 0.64” × 0.062” (29 mm × 16 mm × 1.6 mm) FR4 laminate

PCB with two layers of two ounce copper. The top and bottom side layouts can be seen in Figure 10 and

Figure 11. When looking at the top layer, pin 1 of the LM2854 is on the upper left.

The PCB layout of the LM2854 evaluation board was designed to occupy as little board space as possible,

while still following sound layout guidelines and techniques. The input capacitor, Cin, is placed as close as

possible to the PVIN and PGND pins to minimize stray resistance and inductance between Cin and the

LM2854. Likewise, the AVIN bypass capacitor is placed as close as possible to the AVIN and AGND pins.

PGND and AGND are connected to each other and the ground plane at a single point, the exposed pad of

the LM2854.

Also, in order to help conduct heat to the ground plane and away from the LM2854, a 3 × 3 via array is

used to electrically and thermally connect the exposed pad to the ground plane (instead of a single via).

Additional ground plane vias are located close to the three PGND pins and in the localized ground plane

emanating away from the exposed pad.

Finally, the FB pin trace is intentionally kept as short as possible and routed away from the SW node to

minimize any EMI pickup.

Figure 10. LM2854 Top Side PCB Layout

Figure 11. LM2854 Bottom Side PCB Layout, Viewed from Top

SNVA358B–August 2008–Revised May 2013 AN-1880 LM2854 1MHz Buck Regulator Demo Board

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