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Consideration on permissible dissipation and heat generation

As this IC 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.

=0.0447+0.0319

=0.0766[Ω]

P=3

With the

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

Fig.26 Thermal derating curve

(VQFN020V4040)

Ambient temperature:Ta [℃]

0

25

50

75

100

125

150

0

2.0

3.0

4.0

②

1.21W

①

3.56W

1.0

③

0.70W

④

0.34W

①

4 layers (Copper foil area : 5505mm

copper foil in each layers.

θ

j-a=35.1℃/W

②

4 layers (Copper foil area : 10.29m

copper foil in each layers.

θ

j-a=103.3℃/W

③

4 layers (Copper foil area : 10.29m

θ

j-a=178.6℃/W

④

IC only.

θ

j-a=367.6℃/W

105