Datasheet
LT3080
14
3080fc
Table 2. MSE Package, 8-Lead MSOP
COPPER AREA
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
TOPSIDE* BACKSIDE BOARD AREA
2500mm
2
2500mm
2
2500mm
2
55°C/W
1000mm
2
2500mm
2
2500mm
2
57°C/W
225mm
2
2500mm
2
2500mm
2
60°C/W
100mm
2
2500mm
2
2500mm
2
65°C/W
*Device is mounted on topside
Table 3. DD Package, 8-Lead DFN
COPPER AREA
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
TOPSIDE* BACKSIDE BOARD AREA
2500mm
2
2500mm
2
2500mm
2
60°C/W
1000mm
2
2500mm
2
2500mm
2
62°C/W
225mm
2
2500mm
2
2500mm
2
65°C/W
100mm
2
2500mm
2
2500mm
2
68°C/W
*Device is mounted on topside
Table 4. ST Package, 3-Lead SOT-223
COPPER AREA
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
TOPSIDE* BACKSIDE BOARD AREA
2500mm
2
2500mm
2
2500mm
2
48°C/W
1000mm
2
2500mm
2
2500mm
2
48°C/W
225mm
2
2500mm
2
2500mm
2
56°C/W
100mm
2
2500mm
2
2500mm
2
62°C/W
*Device is mounted on topside
Table 5. Q Package, 5-Lead DD-Pak
COPPER AREA
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
TOPSIDE* BACKSIDE BOARD AREA
2500mm
2
2500mm
2
2500mm
2
25°C/W
1000mm
2
2500mm
2
2500mm
2
30°C/W
125mm
2
2500mm
2
2500mm
2
35°C/W
*Device is mounted on topside
T Package, 5-Lead TO-220
Thermal Resistance (Junction-to-Case) = 3°C/W
Calculating Junction Temperature
Example: Given an output voltage of 0.9V, a V
CONTROL
voltage of 3.3V ±10%, an IN voltage of 1.5V ±5%, output
current range from 1mA to 1A and a maximum ambient
temperature of 50°C, what will the maximum junction
temperature be for the DFN package on a 2500mm
2
board
with topside copper area of 500mm
2
?
of the connections between the regulator and the load.
The data sheet specification for load regulation is Kelvin
sensed at the pins of the package. Negative side sensing
is a true Kelvin connection, with the bottom of the voltage
setting resistor returned to the negative side of the load
(see Figure 7). Connected as shown, system load regula-
tion will be the sum of the LT3080 load regulation and the
parasitic line resistance multiplied by the output current.
It is important to keep the positive connection between
the regulator and load as short as possible and use large
wire or PC board traces.
Thermal Considerations
The LT3080 has internal power and thermal limiting cir-
cuitry designed to protect it under overload conditions.
For continuous normal load conditions, maximum junc-
tion temperature must not be exceeded. It is important
to give consideration to all sources of thermal resistance
from junction to ambient. This includes junction-to-case,
case-to-heat sink interface, heat sink resistance or circuit
board-to-ambient as the application dictates. Additional
heat sources nearby must also be considered.
For surface mount devices, heat sinking is accomplished
by using the heat spreading capabilities of the PC board
and its copper traces. Surface mount heat sinks and plated
through-holes can also be used to spread the heat gener-
ated by power devices.
Junction-to-case thermal resistance is specified from the
IC junction to the bottom of the case directly below the
die. This is the lowest resistance path for heat flow. Proper
mounting is required to ensure the best possible thermal
flow from this area of the package to the heat sinking
material. For the TO-220 package, thermal compound is
strongly recommended for mechanical connections to a
heat sink. A thermally conductive spacer can be used for
electrical isolation as long as the added contribution to
thermal resistance is considered. Note that the Tab or
Exposed Pad (depending on package) is electrically
connected to the output.
The following tables list thermal resistance for several
different copper areas given a fixed board size. All mea-
surements were taken in still air on two-sided 1/16” FR-4
board with one ounce copper.
applicaTions inForMaTion