LT1965IDD-1.8-PBF(RevA) Ver la hoja de datos (PDF) - Linear Technology
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LT1965IDD-1.8-PBF Datasheet PDF : 20 Pages
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LT1965 Series
APPLICATIONS INFORMATION
The following tables list thermal resistance for several
different board sizes and copper areas. All measurements
were taken in still air on 1/16" FR-4 board with one ounce
copper.
Table 1. Measured Thermal Resistance for DFN Package
Copper Area
Topside*
Backside
2500mm2
1000mm2
225mm2
100mm2
50mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
*Device is mounted on topside
Board Area
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
Thermal Resistance
(Junction-to-Ambient)
60°C/W
62°C/W
65°C/W
68°C/W
70°C/W
Table 2. Measured Thermal Resistance for MSOP Package
Copper Area
Topside*
Backside
2500mm2
2500mm2
1000mm2
2500mm2
225mm2
2500mm2
100mm2
2500mm2
50mm2
2500mm2
Board Area
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
Thermal Resistance
(Junction-to-Ambient)
55°C/W
57°C/W
60°C/W
65°C/W
68°C/W
*Device is mounted on topside
Table 3. Measured Thermal Resistance for DD-PAK Package
Copper Area
Topside*
Backside
2500mm2
1000mm2
125mm2
2500mm2
2500mm2
2500mm2
*Device is mounted on topside
Board Area
2500mm2
2500mm2
2500mm2
Thermal Resistance
(Junction-to-Ambient)
25°C/W
30°C/W
35°C/W
Calculating Junction Temperature
Example: Given an output voltage of 2.5V, an input voltage
range of 3.3V ± 5%, an output current range of 0mA to
500mA and a maximum ambient temperature of 85°C,
what will the maximum junction temperature be?
The power dissipated by the device equals:
IOUT(MAX) • (VIN(MAX) – VOUT) + IGND • VIN(MAX)
where:
IOUT(MAX) = 500mA
VIN(MAX) = 3.465V
IGND at (IOUT = 500mA, VIN = 3.465V) = 8.2mA
So,
P = 500mA(3.465V – 2.5V) + 8.2mA(3.465V) = 0.511W
Using a DFN package, the thermal resistance will be in
the range of 60°C/W to 70°C/W depending on the cop-
per area. So the junction temperature rise above ambient
approximately equals:
0.511W • 65°C/W = 33.22°C
The maximum junction temperature equals the maximum
ambient temperature plus the maximum junction tempera-
ture rise above ambient or:
TJMAX = 85°C + 33.22°C = 118.22°C
Measured Thermal Resistance for TO-220 Package
Thermal Resistance (Junction-to-Case) = 3°C/W
1965fa
15
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