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BD9134MUV Datasheet(PDF) 10 Page - Rohm |
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BD9134MUV Datasheet(HTML) 10 Page - Rohm |
10 / 18 page Technical Note 10/17 BD9134MUV www.rohm.com 2009.05 - Rev.A ○ c 2009 ROHM Co., Ltd. All rights reserved. ● 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. P=IOUT 2×RON RON=D×RONP+(1-D)RONN D:ON duty (=VOUT/VCC) RONH:ON resistance of Highside MOS FET RONL:ON resistance of Lowside MOS FET IOUT:Output current If VCC=5V, VOUT=3.3V, RONH=82mΩ, RONL=70mΩ IOUT=3A, for example, D=VOUT/VCC=3.3/5.0=0.66 RON=0.66×0.082+(1-0.66)×0.07 =0.05412+0.0238 =0.07792[Ω] P=3 2×0.07792=0.70128[W] As RONH is greater than RONL 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. 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 2) copper foil in each layers. θ j-a=35.1℃/W ② 4 layers (Copper foil area : 10.29m 2) copper foil in each layers. θ j-a=103.3℃/W ③ 4 layers (Copper foil area : 10.29m 2) θ j-a=178.6℃/W ④ IC only. 105 |
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