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BD9151MUV Datasheet(PDF) 9 Page - Rohm |
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BD9151MUV Datasheet(HTML) 9 Page - Rohm |
9 / 17 page Technical Note BD9151MUV 9/16 www.rohm.com 2009.08 - Rev.A © 2009 ROHM Co., Ltd. All rights reserved. ● 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. If VCC=3.3V, VOUT1=1.8V, VOUT2=1.2V, RONH1=0.27Ω, RONL1=0.18Ω, RONH2=0.27Ω, RONL2=0.18Ω IOUT1=0.4A, IOUT2=0.8A, for example, D1=VOUT1/VCC=1.8/3.3=0.55 D2=VOUT2/VCC=1.2/3.3=0.36 RON1=0.55×0.27+(1-0.55)×0.18 =0.1485+0.081 =0.2295[Ω] RON2=0.36×0.27+(1-0.36)×0.18 =0.0972+0.1152 =0.2124[Ω] P=0.4 2×0.2295+0.82×0.2124=0.173[W] As RONH is greater than RONL in BU9151MUV, 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. Fig.32 Heat radiation characteristics (VQFN020V4040) P=IOUT 2×RON RON=D×RONH+(1-D)RONL D:ON Duty(=VOUT/VCC) RONH:ON resistance of High side MOS FET RONL:ON resistance of Low side MOS FET IOUT:Output current 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 2) (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) (2,3 層に銅箔積層 5505mm 2) θ j-a=103.3℃/W ③ 1 層基板(表層放熱銅箔 10.29mm 2) 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 2) (copper foil in each layers) θ j-a=35.1℃/W ② 4 layers (copper foil area : 10.29mm 2) (copper foil in 2-3 layers: 5505mm 2) θ j-a=103.3℃/W ③ 1 layer (copper foil area : 10.29mm 2) θ j-a=178.6℃/W ④ IC only θ j-a=367.6℃/W |
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