LT1083 LINER [Linear Technology], LT1083 Datasheet - Page 9

• Manufacturer Part Number: LT1083
• Description: 3A, 5A, 7.5A Low Dropout Positive Fixed Regulators
• Manufacturer: LINER [Linear Technology]

APPLICATIONS
thermal resistance specifications have been developed to
more accurately reflect device temperature and ensure
safe operating temperatures. The data section for these
new regulators provides a separate thermal resistance and
maximum junction temperature for both the Control Sec-
tion and the Power Section . Previous regulators, with a
single junction-to-case thermal resistance specification,
used an average of the two values provided here and
therefore could allow excessive junction temperatures
under certain conditions of ambient temperature and heat
sink resistance. To avoid this possibility, calculations
should be made for both sections to ensure that both
thermal limits are met.
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 sink. Thermal
compound at the case-to-heat sink interface is strongly
recommended. If the case of the device must be electroni-
cally isolated, a thermally conductive spacer can be used
as long as its added contribution to thermal resistance is
considered. Note that the case of all devices in this series
is electronically connected to the ouput.
TYPICAL APPLICATIONS
U
INPUT
28V
INFORMATION
U
10k
U
W
1k
1M
LT1011
U
MR1122
High Efficiency Regulator
+
–
1mH
10,000µF
1N914
28V
+
4N28
For example, using a LT1083-5CK (TO-3, Commercial)
and assuming:
Power dissipation under these conditions is equal to:
Junction temperature will be equal to:
For the Control Section:
For the Power Transistor:
In both cases the junction temperature is below the
maximum rating for the respective sections, ensuring
reliable operation.
10k
10k
V
T
thermal compound.
P
T
T
118 C
118 C < 125 C = T
cial Range)
T
142 C
142 C < 150 C = T
cial Range)
A
CASE-TO-HEAT SINK
J
J
J
IN
D
470
= T
= 75 C 24W (1 C/W 0.2 C/W 0.6 C/W) =
= 75 C 24W (1 C/W 0.2 C/W 1.6 C/W) =
= 75 C
1N914
(max continuous) = 9V, V
= (V
28V
A
IN
IN
LT1083/4/5 TA03
P
– V
LT1083-5 OUT
D
GND
HEAT SINK
(
OUT
HEAT SINK
) (I
LT1083/84/85 Fixed
= 0.2 C/W for K package with
JMAX
JMAX
OUT
= 1 C/W,
) = 24W
(Control Section Commer-
(Power Transistor Commer-
OUTPUT
CASE-TO-HEAT SINK
OUT
= 5V, I
OUT
= 6A,
+
JC
9
)