BD3539FVM,BD3539NUX

Technical Note

10/11

www.rohm.com

2009.10 - Rev.A

© 2009 ROHM Co., Ltd. All rights reserved.

●

Heat loss

Thermal design must be conducted with the operation under the conditions listed below (which are the guaranteed

temperature range requiring consideration on appropriate margins etc);

1: Ambient temperature Ta: 100℃ or lower

2:Chip junction temperature Tj: 150℃ or lower

The chip junction temperature Tj can be considered as follows:

Because package with FIN is used at IC bottom side, package power changes considerably by copper foil area, which is

connected. Please radiate heat by taking enough area for board surface or using many through hole to inner layer pattern.

Most of heat loss in BD3539FVM/NUX occurs at the output N-channel FET. The power lost is determined by multiplying the

voltage between VIN and Vo by the output current. As this IC employs the power PKG, the thermal derating characteristics

significantly depends on the pc board conditions. When designing, care must be taken to the size of a pc board to be used.

VDDQ)×Io(Ave)

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Heat dissipation characteristics [Tc]

◎

MSOP8

●

Heat dissipation characteristics [Ta]

◎

MSOP8

◎

VSON008X2030

①

Calculation based on IC surface

temperature Tc, mounted on a board

Tj=Tc+θj-c×W

②

Calculation based on ambient temperature Ta

Tj=Ta+θj-a×W

With no heat sink

1-layer board(copper foil area:70×70mm

4-layer board(copper foil area:70×70mm

PCB size: 70×70×1.6mm

θ

j-a:VSON008X2030 516.5℃/W

242.7℃/W

142.5℃/W

＜

Reference example＞

θ

j-a:MSOP-8

212.8℃/W

322.6℃/W

With no heat sink

1-layer board(copper foil area :70×70mm

2.72W

[W]

0

25

75

100

125

50

1.0

0.5

0

3.0

2.5

150

[℃]

1-layer board

θ

ja=46.0℃/W

2.0

1.5

Ambient Temperature [Ta]

PCB size:70×70×1.6mm

(Board copper foil area: :70×70mm

<Reference example>

θ

j-c:MSOP-8 46.0℃/W

[W]

0

25

75

100

125

150

50

[℃]

Ambient Temperature [Ta]

0.5

0.25

0

1.0

0.75

(1) 877.2mW

(2) 515.0mW

(3) 242.0mW

(1) 4-layer board（copper foil area : 5505mm

Every layer has copper foil area,θja=142.5℃/W

(2) 1-layer board

θ

ja=242.7℃/W

(3) With no heat sink

θ

ja=516.5℃/W

(1) 587.4mW

[mW]

0

25

75

100

125

50

200

100

0

600

500

150

[℃]

(1) 1-layer board

θ

ja=212.8℃/W

(2) with no heat sink

θ

ja=322.6℃/W

400

300

Ambient Temperature [Ta]

(2) 387.4mW

= 0.375(W)

Power consumption(W) = 1.5(V)-0.75(V) ×0.5(A)

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