LM1085IS-3.3 National Semiconductor, LM1085IS-3.3 Datasheet - Page 9

• Manufacturer Part Number: LM1085IS-3.3
• Description: Linear Voltage Regulator IC
• Manufacturer: National Semiconductor

Specifications of LM1085IS-3.3

• No. Of Pins: 3
• Output Current: 3A
• Termination Type: SMD
• Mounting Type: Through Hole
• Voltage Regulator Type: LDO Linear
• Peak Reflow Compatible (260 C): No
• Current Rating: 3A
• Output Voltage Max: 3.3V
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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 LM1085 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
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)
(max, OUTPUT SECTION) = (150˚C - T
FIGURE 7. Heat sink thermal Resistance vs Area
(max, CONTROL SECTION) = (125˚C - T
is 150˚C for the output section.
JA(max)
HA(max)
=
should be calculated separately for each section as
= T
should also be calculated twice as follows:
=
FIGURE 6. Power Dissipation Diagram
=
JA
R(max)
JA(max)
J(max)
JA
(max, OUTPUT SECTION) - (
) is calculated as:
CH
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
)
values to determine the appropriate
J(max
+
HA(max)
CH
− T
CH
)
A(max)
).
can be estimated at 0.2
(Continued)
DS100947-64
)/P
D
A(max)
J(max)
A(max)
DS100947-16
JC
)/P
(OUTPUT
) for each
JC
)/P
D
CH
(CON-
D
can
J -
9
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