1.

Place the LM3203 on 10.82 mil pads. As a thermal relief,

connect to each pad with a 7 mil wide, approximately 7

mil long traces, and when incrementally increase each

trace to its optimal width. The important criterion is sym-

metry to ensure the solder bumps on the LM3203 re-flow

evenly (see Micro SMD Package Assembly and Use).

2.

Place the LM3203, inductor and filter capacitors close

together and make the trace short. The traces between

these components carry relatively high switching cur-

rents and act as antennas. Following this rule reduces

radiated noise. Place the capacitors and inductor close

to the LM3203. The input capacitor should be placed

right next to the device between PV

3.

Arrange the components so that the switching current

loops curl in the same direction. During the first half of

each cycle, current flows from the input filter capacitor,

through the LM3203 and inductor to the output filter

capacitor and back through ground, forming a current

loop. In the second half of each cycle, current is pulled

up from ground, through the LM3203 by the inductor, to

the output filter capacitor and then back through ground,

forming a second current loop. Routing these loops so

the current curls in the same direction, prevents mag-

netic field reversal between the two half-cycles and re-

duces radiated noise.

4.

Connect the ground pins of the LM3203, and filter ca-

pacitors together using generous component side cop-

per fill as a pseudo-ground plane. Then connect this to

the ground-plane (if one is used) with several vias. This

reduces ground plane noise by preventing the switching

currents from circulating through the ground plane. It

also reduces ground bounce at the LM3203 by giving it

a low impedance ground connection.

5.

Use wide traces between the power components and for

power connections to the DC-DC converter circuit. This

reduces voltage errors caused by resistive losses across

the traces.

6.

Route noise sensitive traces, such as the voltage feed-

back trace, away from noisy traces and components.

The voltage feedback trace must remain close to the

LM3203 circuit and should be routed directly from FB pin

to V

route the feedback trace on another layer and to have a

ground plane between the top layer and the layer on

which the feedback trace is routed. This reduces EMI

radiation on to the DC-DC converter’s own voltage feed-

back trace.

7.

It is recommended to connect BYPOUT pin to V

the output capacitor using a separate trace, instead of

connecting it directly to the FB pin for better noise

immunity.

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