LT3082 Ver la hoja de datos (PDF) - Linear Technology
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LT3082 Datasheet PDF : 20 Pages
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LT3082
APPLICATIONS INFORMATION
Tables 3 through 5 list thermal resistance as a function
of copper areas in a fixed board size. All measurements
were taken in still air on a 4-layer FR-4 board with 1oz
solid internal planes and 2oz external trace planes with a
total finished board thickness of 1.6mm.
Table 3. DD Package, 8-Lead DFN
COPPER AREA
TOPSIDE* BACKSIDE BOARD AREA
2500mm2 2500mm2 2500mm2
1000mm2 2500mm2 2500mm2
225mm2 2500mm2 2500mm2
100mm2 2500mm2 2500mm2
*Device is mounted on topside
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
25°C/W
25°C/W
28°C/W
32°C/W
Table 4. TS8 Package, 8-Lead SOT-23
COPPER AREA
TOPSIDE* BACKSIDE BOARD AREA
2500mm2 2500mm2 2500mm2
1000mm2 2500mm2 2500mm2
225mm2 2500mm2 2500mm2
100mm2 2500mm2 2500mm2
*Device is mounted on topside
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
54°C/W
54°C/W
57°C/W
63°C/W
Table 5. ST Package, 3-Lead SOT-223
COPPER AREA
TOPSIDE* BACKSIDE BOARD AREA
2500mm2 2500mm2 2500mm2
1000mm2 2500mm2 2500mm2
225mm2
100mm2
2500mm2
2500mm2
2500mm2
2500mm2
*Device is mounted on topside
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
20°C/W
20°C/W
24°C/W
29°C/W
For further information on thermal resistance and using thermal information,
refer to JEDEC standard JESD51, notably JESD51-12.
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.
Demo circuit 1447A’s board layout using multiple inner
VOUT planes and multiple thermal vias achieves 28°C/W
performance for the DFN package.
Calculating Junction Temperature
Example: Given an industrial factory application with an
input voltage of 15V ±10%, an output voltage of 12V ±5%,
an output current of 200mA and a maximum ambient
temperature of 50°C, what would be the maximum junc-
tion temperature for a DFN package?
The total circuit power equals:
PTOTAL = (VIN – VOUT)(IOUT)
The SET pin current is negligible and can be ignored.
VIN(MAX CONTINUOUS) = 16.5 (15V + 10%)
VOUT(MIN CONTINUOUS) = 11.4V (12V – 5%)
IOUT = 200mA
Power dissipation under these conditions equals:
PTOTAL = (16.5 – 11.4V)(200mA) = 1.02W
Junction temperature equals:
TJ = TA + PTOTAL • θJA
TJ = 50°C + (1.02W • 30°C/W) = 80.6°C
In this example, junction temperature is below the maxi-
mum rating, ensuring reliable operation.
3082f
13
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