LM2637 datasheet(16/17 Pages) NSC

16 / 17 page

Applications Information (Continued)

Try to use 2 oz. copper for the ground plane if tight load

regulation is desired. In the case of dynamic voltage po-

sitioning, this may not be a concern because the loose

load regulation is desired anyway. However, do not for-

get to take into consideration the voltage drop caused by

the ground plane when calculating dynamic voltage po-

sitioning parameters.

Try to keep gate drive traces short. However, do not

make them too short or else the LM2637 may be placed

too close to the FETs and get heated up by them. For the

same reason, do not use wide traces, 10 mil traces

should be enough.

When not employing dynamic voltage positioning, place

the feedback point at the VRM connector pins so as to

have a tight load regulation. If it is an embedded power

supply, place the feedback point at Slot I connector or

wherever closest to the MPU.

Start component placement with the power devices such

as FETs, and inductors.

Do not place the LM2637 directly underneath the FETs

(on the other side of the PCB) when surface mount FETs

are used. Also try to avoid staying too close to the output

inductor, especially when using an open core inductor.

If possible, keep the capacitors some distance away

from the inductors and FET heatsinks so that the capaci-

tors will have a better thermal environment. Keep in

mind that the input capacitors are usually much hotter

than output capacitors.

When

implementing

dynamic

voltage

positioning

through a PCB trace, keep in mind that the PCB trace is

a heat source and try to avoid placing the trace directly

underneath the LM2637.

Try to place a ceramic capacitor as close as possible to

the V

DD pin.

If it is a MPU core supply, try to place the output bulk ca-

pacitors fairly close to the MPU for lower inductance.

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