LT3080EST datasheet(13/26 Pages) LINER

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LT3080

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Table 2. MSE Package, 8-Lead MSOP

COPPER AREA

THERMAL RESISTANCE

(JUNCTION-TO-AMBIENT)

TOPSIDE*

BACKSIDE

BOARD AREA

2500mm2

55°C/W

1000mm2

2500mm2

57°C/W

225mm2

2500mm2

60°C/W

100mm2

2500mm2

65°C/W

*Device is mounted on topside

Table 3. DD Package, 8-Lead DFN

COPPER AREA

THERMAL RESISTANCE

(JUNCTION-TO-AMBIENT)

TOPSIDE*

BACKSIDE

BOARD AREA

2500mm2

60°C/W

1000mm2

2500mm2

62°C/W

225mm2

2500mm2

65°C/W

100mm2

2500mm2

68°C/W

*Device is mounted on topside

Table 4. ST Package, 3-Lead SOT-223

COPPER AREA

THERMAL RESISTANCE

(JUNCTION-TO-AMBIENT)

TOPSIDE*

BACKSIDE

BOARD AREA

2500mm2

48°C/W

1000mm2

2500mm2

48°C/W

225mm2

2500mm2

56°C/W

100mm2

2500mm2

62°C/W

*Device is mounted on topside

Table 5. Q Package, 5-Lead DD-Pak

COPPER AREA

THERMAL RESISTANCE

(JUNCTION-TO-AMBIENT)

TOPSIDE*

BACKSIDE

BOARD AREA

2500mm2

25°C/W

1000mm2

2500mm2

30°C/W

125mm2

2500mm2

35°C/W

*Device is mounted on topside

T Package, 5-Lead TO-220

Thermal Resistance (Junction-to-Case) = 3°C/W

Calculating Junction Temperature

Example: Given an output voltage of 0.9V, a VCONTROL

voltage of 3.3V ±10%, an IN voltage of 1.5V ±5%, output

current range from 1mA to 1A and a maximum ambient

temperature of 50°C, what will the maximum junction

temperature be for the DFN package on a 2500mm2 board

with topside copper area of 500mm2?

of the connections between the regulator and the load.

The data sheet speciﬁcation for load regulation is Kelvin

sensed at the pins of the package. Negative side sensing

is a true Kelvin connection, with the bottom of the voltage

setting resistor returned to the negative side of the load

(see Figure 7). Connected as shown, system load regula-

tion will be the sum of the LT3080 load regulation and the

parasitic line resistance multiplied by the output current.

It is important to keep the positive connection between

the regulator and load as short as possible and use large

wire or PC board traces.

Thermal Considerations

The LT3080 has internal power and thermal limiting cir-

cuitry designed to protect it under overload conditions.

For continuous normal load conditions, maximum junc-

tion temperature must not be exceeded. It is important

to give consideration to all sources of thermal resistance

from junction to ambient. This includes junction-to-case,

case-to-heat sink interface, heat sink resistance or circuit

board-to-ambient as the application dictates. Additional

heat sources nearby must also be considered.

For surface mount devices, heat sinking is accomplished

by using the heat spreading capabilities of the PC board

and its copper traces. Surface mount heat sinks and plated

through-holes can also be used to spread the heat gener-

ated by power devices.

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 sinking

material. For the TO-220 package, thermal compound is

strongly recommended for mechanical connections to a

heat sink. A thermally conductive spacer can be used for

electrical isolation as long as the added contribution to

thermal resistance is considered. Note that the Tab or

Exposed Pad (depending on package) is electrically

connected to the output.

The following tables list thermal resistance for several

different copper areas given a ﬁxed board size. All mea-

surements were taken in still air on two-sided 1/16” FR-4

board with one ounce copper.

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