Datasheet

LT3507A
21
3507af
Figure 12. Subtracting the Current When the Switch Is On (12a) from the Current When the Switch Is Off (12b)
Reveals the Path of the High Frequency Switching Current (12c)
APPLICATIONS INFORMATION
Figure 13. Power Path Components and Topside Layout
V
IN
SW
I
OUT
– I
IN
I
IN
I
IN
I
IN
I
OUT
I
OUT
I
OUT
I
IN
GND
(12a Switch On)
V
IN
V
SW
C1 D1 C2
3507A F12
L1
SW
GND
(12c High Frequency Switching Loop)
V
IN
SW
GND
(12b Switch Off)
I
C1
THERMAL CONSIDERATIONS
The high output current capability of the LT3507A will
require careful attention to power dissipation of all the
components to insure a safe thermal design. The PCB
must provide heat sinking to keep the LT3507A cool.
The exposed pad on the bottom of the package must be
soldered to a ground plane. This ground should be tied
to other copper layers below with thermal vias; these lay-
ers will spread the heat dissipated by the LT3507A. Place
additional vias near the catch diodes. Adding more copper
to the top and bottom layers and tying this copper to the
internal planes with vias can reduce thermal resistance
further. With these steps, the thermal resistance from die
(or junction) to ambient can be reduced to θ
JA
= 34°C/W
or less (QFN). With 100 LFPM airflow, this resistance can
fall by another 25%. Further increases in airflow will lead
to lower thermal resistance.