Datasheet

LT3092
13
3092fb
APPLICATIONS INFORMATION
interface, heat sink resistance or circuit board-to-ambient
as the application dictates. Consider all additional, adjacent
heat generating sources in proximity on the PCB.
Surface mount packages provide the necessary heat
sinking by using the heat spreading capabilities of the
PC board, copper traces and planes. Surface mount heat
sinks, plated through-holes and solder fi lled vias can also
spread the heat generated by power devices.
Junction-to-case thermal resistance is specifi ed from the
IC junction to the bottom of the case directly, or the bottom
of the pin most directly, in the heat path. This is the lowest
thermal resistance path for heat fl ow. Only proper device
mounting ensures the best possible thermal fl ow from this
area of the package to the heat sinking material.
Note that the Exposed Pad of the DFN package and the
Tab of the SOT-223 package are electrically connected
to the output (V
OUT
).
The following tables list thermal resistance as a function
of copper areas in a fi xed board size. All measurements
were taken in still air on a four-layer FR-4 board with 1oz
solid internal planes and 2oz external trace planes with a
total fi nished board thickness of 1.6mm.
PCB layers, copper weight, board layout and thermal vias
affect the resultant thermal resistance. Please reference
JEDEC standard JESD51-7 for further information on high
thermal conductivity test boards. Achieving low thermal
resistance necessitates attention to detail and careful layout.
Figure 8. Connect Two LT3092s for Higher Current
Figure 9. Parallel Devices
3092 F08
1.33 1.33
300 300
I
OUT
I
OUT
, 300mA
+
–
LT3092
10µA 10µA
+
–
LT3092
20k20k
IN IN
SET SETOUTOUTOUTOUT
3092 F09
I
OUT
I
OUT
, 400mA
+
–
LT3092
10µA
+
–
LT3092
10µA
R
2.5
R
x
50k
40m*
40m*
*40m PC BOARD TRACE
1V
IN IN
SET SET
R
VR
x
IN MAX
=
()
•
%90