BD9132MUV_14 Datasheet, PDF (12/26 Pages) Rohm – Synchronous Buck Converter with Integrated FET

BD9132MUV
5. Consideration on Permissible Dissipation and Heat Generation
Since 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. This
is because conduction losses are the most significant among other dissipation mentioned above such as gate
charge/discharge dissipation and switching dissipation.
4.0
①3.56W
3.0
2.0
① 4 layers (Copper foil area : 5505mm²)
copper foil in each layers.
θj-a=35.1°C/W
② 4 layers (Copper foil area : 10.29m²)
copper foil in each layers.
θj-a=103.3°C/W
③ 1 layers (Copper foil area : 10.29m²)
θj-a=178.6°C/W
④IC only.
θj-a=367.6°C/W
②1.21W
1.0
③0.70W
④0.34W
0
0 25 50
75 100105 125 150
Ambient Temperature: Ta [°C]
Figure 27. Thermal Derating Curve
(VQFN020V4040)
P  I_OUT ²  R_ON
R_ON  D  R_ONH  1  DR_ONL
where:
D is the ON duty (=VOUT/VCC).
RONH is the ON-Resistance of High Side MOSFET.
RONL is the ON-Resistance of Low Side MOSFET.
IOUT is the Output current.
If VCC=3.3V, VOUT=1.8V, RONH=82mΩ, RONL=70mΩ
IOUT=3A, for example,
D  V_OUT / V_CC  1.8 / 3.3  0.545
R_ON  0.545 0.082 1 0.545 0.07
 0.0447 0.0319
 0.0766 
P  3²  0.0766  0.6894 W 
Since RONP is greater than RONN in this IC, the dissipation increases as the ON duty increases. Taking into consideration the
dissipation stated above, thermal design must be carried out with sufficient margin.
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TSZ22111・15・001
12/22
TSZ02201-0J3J0AJ00140-1-2
03.Oct.2014 Rev.002