bd91361muv ROHM Co. Ltd., bd91361muv Datasheet - Page 11

• Manufacturer Part Number: bd91361muv
• Description: Single-chip Type With Built-in Fet Switching Regulators
• Manufacturer: ROHM Co. Ltd.

●Consideration on permissible dissipation and heat generation
BD91361MUV
© 2010 ROHM Co., Ltd. All rights reserved.
www.rohm.com
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
With the consideration on the dissipation as above, thermal design must be carried out with sufficient margin allowed.
ONH
4
3
2
1
0
is greater than R
0
①3.56W
②2.21W
③0.70W
④0.34W
If V
CC
I
25
OUT
=3.3V, V
Ambient temperature:Ta [℃]
Fig.29 Thermal derating curve
=4A, for example,
R
P=4
ON
D=V
ONL
50
2
=0.0327+0.0250
=0.0577[Ω]
=0.545×0.06+(1-0.545)×0.055
(VQFN020V4040)
OUT
×0.0577=0.2309[W]
OUT
in this IC, the dissipation increases as the ON duty becomes greater.
=1.8V, R
① 4 layers (Copper foil area : 5505mm
② 4 layers (1
(2
③ 1 layer (Copper foil area : 10.29m
④ IC only.
/V
nd
copper foil in each layers.
θ j-a=35.1 ℃ /W
and 3
θ j-a=56.6 ℃ /W
θ j-a=178.6 ℃ /W
θ j-a=367.6 ℃ /W
75
CC
=1.8/3.3=0.545
rd
copper foil area: 5505m
ONH
st
and 4
100
=60mΩ, R
th
copper foil area : 10.29m
105
125
2
)
2
)
ONL
2
)
11/17
=55mΩ
2
150
)
P=I
R
D
R
R
I
OUT
ON
ONH
ONL
OUT
=D×R
: ON duty (=V
: ON resistance of Highside MOS FET
: ON resistance of Lowside MOS FET
: Output current
2
×R
ONP
ON
+(1-D)R
OUT
ONN
/V
CC
)
Technical Note
2010.06 - Rev.A