LT1764A LINER [Linear Technology], LT1764A Datasheet - Page 11

• Manufacturer Part Number: LT1764A
• Description: 1.1A, Low Noise, Low Dropout Linear Regulator
• Manufacturer: LINER [Linear Technology]

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
*Device is mounted on topside
Table 2. Measured Thermal Resistance for MSOP Package
*Device is mounted on topside
Table 3. Measured Thermal Resistance for DD-PAK Package
*Device is mounted on topside
Measured Thermal Resistance for TO-220 Package
Thermal Resistance (Junction-to-Case) = 3°C/W
2500mm
1000mm
2500mm
1000mm
2500mm
1000mm
Topside*
Topside*
Topside*
225mm
100mm
225mm
100mm
125mm
50mm
50mm
Copper Area
Copper Area
Copper Area
2
2
2
2
2
2
2
2
2
2
2
2
2
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
Backside
Backside
Backside
2
2
2
2
2
2
2
2
2
2
2
2
2
Board Area
Board Area
Board Area
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2
2
2
2
2
2
2
2
2
2
2
2
2
(Junction-to-Ambient)
(Junction-to-Ambient)
(Junction-to-Ambient)
Thermal Resistance
Thermal Resistance
Thermal Resistance
60°C/W
62°C/W
65°C/W
68°C/W
70°C/W
55°C/W
57°C/W
60°C/W
65°C/W
68°C/W
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:
where:
So,
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:
The maximum junction temperature equals the maximum
ambient temperature plus the maximum junction tempera-
ture rise above ambient or:
I
I
V
I
P = 500mA(3.465V – 2.5V) + 8.2mA(3.465V) = 0.511W
0.511W • 65°C/W = 33.22°C
T
OUT(MAX)
OUT(MAX)
GND
JMAX
IN(MAX)
at (I
= 85°C + 33.22°C = 118.22°C
= 3.465V
OUT
• (V
= 500mA
= 500mA, V
IN(MAX)
– V
OUT
IN
= 3.465V) = 8.2mA
) + I
GND
• V
IN(MAX)
LT1965
11
1965f