Datasheet

LT1965 Series
15
1965fb
For more information www.linear.com/LT1965
applications inForMation
The following tables list thermal resistance for several
different board sizes and copper areas. All measurements
were taken in still air on a 2-layer 1/16" FR-4 board with
one ounce copper.
Table 1. Measured Thermal Resistance for DFN Package
Copper Area Thermal Resistance
Topside* Backside Board Area (Junction-to-Ambient)
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
50mm
2
2500mm
2
2500mm
2
70°C/W
*Device is mounted on topside
Table 2. Measured Thermal Resistance for MSOP Package
Copper Area Thermal Resistance
Topside* Backside Board Area (Junction-to-Ambient)
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
50mm
2
2500mm
2
2500mm
2
68°C/W
*Device is mounted on topside
Table 3. Measured Thermal Resistance for DD-Pak Package
Copper Area Thermal Resistance
Topside* Backside Board Area (Junction-to-Ambient)
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
Measured Thermal Resistance for TO-220 Package
Thermal Resistance (Junction-to-Case) = 3°C/W
Calculating Junction Temperature
Example: Given an output voltage of 2.5V, an input volt
-
age 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:
I
OUT(MAX)
• (V
IN(MAX)
– V
OUT
) + I
GND
V
IN(MAX)
where:
I
OUT(MAX)
= 500mA
V
IN(MAX)
= 3.465V
I
GND
at (I
OUT
= 500mA, V
IN
= 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:
T
JMAX
= 85°C + 33.22°C = 118.22°C
Protection Features
The LT
1965 regulators incorporate several protection
features that makes them ideal for use in battery-powered
circuits. In addition to the normal protection features
associated with monolithic regulators, such as current
limiting and thermal limiting, the devices also protect
against reverse-input voltages, reverse-output voltages
and reverse output-to-input voltages.
Current-limit protection and thermal overload protection
protect the device against current overload conditions
at its output. For normal operation, do not exceed the
maximum rated junction temperature of 125°C (LT1965E,
LT1965I) or 150°C (LT1965H).
Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.