bd9137muv ROHM Co. Ltd., bd9137muv Datasheet - Page 8

• Manufacturer Part Number: bd9137muv
• Description: High Efficiency Step-down Switching Regulator
• Manufacturer: ROHM Co. Ltd.

●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.
As R
the dissipation as above, thermal design must be carried out with sufficient margin allowed.
ONH
is greater than R
1.0
3.0
2.0
4.5
4.0
If V
0
0
②2.21W
①3.56W
③0.70W
④0.34W
CC
I
OUT
=3.3V, V
Fig.26 Thermal derating curve
=3A, for example,
25
R
P=3
ON
D=V
Ambient temperature:Ta [℃]
2
=0.0447+0.0319
=0.0766[Ω]
=0.545×0.082+(1-0.545)×0.07
ONL
OUT
×0.0766＝0.6894[W]
(VQFN020V4040)
OUT
50
=1.8V, R
in this IC, the dissipation increases as the ON duty becomes greater. With the consideration on
/V
CC
① 4 layers (copper foil area : 5505mm
② 4 layers (1st,4thcopper foil area : 10.29mm
③ 1 layer (copper foil area :10.29mm
④IC only
=1.8/3.3=0.545
75
(copper foil in each layers)
θj-a=35.1℃/W
(2nd ,3rd copper foil area : 5505mm
θj-a=56.6℃/W
θj-a=178.6℃/W
θj-a=367.6℃/W
ONH
=82mΩ, R
100
105
125
ONL
=70mΩ
2
2
8/16
)
2
)
)
150
2
)
P=I
R
D：ON duty (=V
R
R
I
OUT
ON
ONH
ONL
OUT
=D×R
：Output current
：ON resistance of Lowside MOS FET
：ON resistance of Highside MOS FET
2
×R
ONP
ON
+(1-D)R
OUT
/V
CC
ONN
)