Technical Note

BD9151MUV

9/16

www.rohm.com

2009.08 - Rev.A

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

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Consideration on permissible dissipation and heat generation

As BU9151MUV functions with high efficiency without significant heat generation in most applications, no special consideration

is needed on permissible dissipation or heat generation. In case of extreme conditions, however, including lower input voltage,

higher output voltage, heavier load, and/or higher temperature, the permissible dissipation and/or heat generation must be

carefully considered.

For dissipation, only conduction losses due to DC resistance of inductor and ON resistance of FET are considered. Because

the conduction losses are considered to play the leading role among other dissipation mentioned above including gate

charge/discharge dissipation and switching dissipation.

=0.1485+0.081

=0.2295[Ω]

=0.0972+0.1152

=0.2124[Ω]

P=0.4

With the consideration on the dissipation as above, thermal design must be carried out with sufficient margin allowed.

Fig.32 Heat radiation characteristics (VQFN020V4040)

0

25

50

75

100

125

150

0

2.0

3.0

4.0

②

2.21W

①

3.56W

1.0

③

0.70W

④

0.34W

①

4 層基板(表層放熱銅箔 5505mm

(各層に銅箔積層)

θ

j-a=35.1℃/W

②

4 層基板(表層放熱銅箔 10.29mm

(2,3 層に銅箔積層 5505mm

θ

j-a=103.3℃/W

③

1 層基板(表層放熱銅箔 10.29mm

θ

j-a=178.6℃/W

④

IC 単体時

θ

j-a=367.6℃/W

105

Ambient Temperature :Ta [℃]

①

4 layers (copper foil area : 5505mm

(copper foil in each layers)

θ

j-a=35.1℃/W

②

4 layers (copper foil area : 10.29mm

(copper foil in 2-3 layers: 5505mm

θ

j-a=103.3℃/W

③

1 layer (copper foil area : 10.29mm

θ

j-a=178.6℃/W

④

IC only

θ

j-a=367.6℃/W