BD8963EFJ(2010) Ver la hoja de datos (PDF) - ROHM Semiconductor

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BD8963EFJ
(Rev.:2010)

Low Noise High-efficiency Switching Regulator with Built-in Power MOSFET

ROHM Semiconductor 

BD8963EFJ

Technical Note

●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.

4

⑤3.76W

3

① IC only

θj-a=249.5℃/W

②1 layers（copper foil area:0mm×0mm）

θj-a=153.2℃/W

③2 layers（copper foil area:15mm×15mm）

θj-a=113.6℃/W

④2 layers（copper foil area:70mm×70mm）

θj-a=59.2℃/W

⑤4 layers（copper foil area:70mm×70mm）

θj-a=33.3℃/W

(when mounted on a board 70mm×70mm×1.6mm

Glass-epoxy PCB with termal Via)

P=IOUT2×RON

RON=D×RONP+(1-D)RONN

D：ON duty (=VOUT/VCC)

RCOIL：DC resistance of coil

RONP：ON resistance of P-channel MOS FET

RONN：ON resistance of N-channel MOS FET

IOUT：Output current

④2.11W

2

③1.10W

1

②0.82W

①0.50W

0

0

25

50

75 85 100

125

150

Ambient temperature:Ta [℃]

Fig.24 Thermal derating curve

(HTSOP-J8)

Ex.)VCC=5V, VOUT=1.1V, RONP=0.145Ω, RONN=0.08Ω

IOUT=3A, for example,

D=VOUT/VCC=1.1/5=0.22

RON=0.22×0.145+(1-0.22)×0.08

=0.0319+0.0624

=0.0943[Ω]

P=32×0.0943=0.8487[W]

As RONP is greater than RONN in this IC, the dissipation increases as the ON duty becomes greater.

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

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9/17

2010.06 - Rev.A

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