lt3580ems8e-trpbf Linear Technology Corporation, lt3580ems8e-trpbf Datasheet - Page 17

• Manufacturer Part Number: lt3580ems8e-trpbf
• Description: Boost/inverting Dc/dc Converter With 2a Switch, Soft-start, And Synchronization
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
Board layout also has a signifi cant effect on thermal re-
sistance. The exposed package ground pad is the copper
plate that runs under the LT3580 die. This is a good thermal
path for heat out of the package. Soldering the pad onto
the board reduces die temperature and increases the power
capability of the LT3580. Provide as much copper area as
possible around this pad. Adding multiple feedthroughs
around the pad to the ground plane will also help. Figures
9 and 10 show the recommended component placement
for the boost and SEPIC confi gurations, respectively.
Layout Hints for Inverting Topology
Figure 11 shows recommended component placement for
the dual inductor inverting topology. Input bypass capacitor,
C1, should be placed close to the LT3580, as shown. The
load should connect directly to the output capacitor, C2,
Figure 8. High Speed “Chopped” Switching Path for Boost Topology
V
IN
C1
LT3580
GND
SW
L1
FREQUENCY
SWITCHING
HIGH
PATH
for best load regulation. You can tie the local ground into
the system ground plane at the C3 ground terminal.
The cut ground copper at D1’s cathode is essential to
obtain low noise. This important layout issue arises due
to the chopped nature of the currents fl owing in Q1 and
D1. If they are both tied directly to the ground plane be-
fore being combined, switching noise will be introduced
into the ground plane. It is almost impossible to get rid
of this noise, once present in the ground plane. The solu-
tion is to tie D1’s cathode to the ground pin of the LT3580
before the combined currents are dumped in the ground
plane as drawn in Figure 2, Figure 12 and Figure 13. This
single layout technique can virtually eliminate high
frequency “spike” noise, so often present on switching
regulator outputs.
D1
C2
LOAD
3580 F08
V
OUT
LT3580
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