LM1084IS-12 National Semiconductor, LM1084IS-12 Datasheet - Page 10

• Manufacturer Part Number: LM1084IS-12
• Description: 5A Low Dropout Positive Regulators
• Manufacturer: National Semiconductor

www.national.com
APPLICATION NOTE
Figure 6 shows the voltages and currents which are present
in the circuit.
Once the devices power is determined, the maximum allow-
able (
The LM1084 has different temperature specifications for two
different sections of the IC: the control section and the output
section. The Electrical Characteristics table shows the junc-
tion to case thermal resistances for each of these sections,
while the maximum junction temperatures (T
section is listed in the Absolute Maximum section of the
datasheet. T
(max)
follows:
The required heat sink is determined by calculating its re-
quired thermal resistance (
(
(
TROL SECTION) +
(
SECTION) +
If thermal compound is used,
C/W. If the case is soldered to the heat sink, then a
be estimated as 0 C/W.
After,
lower of the two
ate heat sink.
If PC board copper is going to be used as a heat sink, then
Figure 7 can be used to determine the appropriate area
(size) of copper foil required.
JA (max)
JA (max)
JA
JA
HA (max)
HA (max)
HA (max)
HA (max)
FIGURE 7. Heat sink thermal Resistance vs Area
(max, CONTROL SECTION) = (125˚C - T
(max, OUTPUT SECTION) = (150˚C - T
is 150˚C for the output section.
JA (max)
HA (max)
should be calculated separately for each section as
FIGURE 6. Power Dissipation Diagram
= T
) =
=
) should also be calculated twice as follows:
) =
J(max)
R(max)
JA (max)
) is calculated as:
JA
JA
CH
(max, OUTPUT SECTION) - (
is calculated for each section, choose the
)
(max, CONTROL SECTION) - (
HA (max)
/P
is 125˚C for the control section, while T
D
− (
CH
= T
)
JC
J(max)
values to determine the appropri-
+
HA (max)
CH
CH
− T
)
can be estimated at 0.2
).
A(max)
(Continued)
DS100946-64
/P
D
A(max)
J(max)
A(max)
DS100946-16
JC
(OUTPUT
) for each
)P
JC
)/P
D
CH
(CON-
D
can
J -
10