BD9130NV_14 Datasheet, PDF (12/25 Pages) Rohm – Synchronous Buck Converter with Integrated FET

BD9130NV
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.
①3.9W
4.0
3.0
2.0
①for SON008V5060
JEDEC 4 layer board 76.2x114.3x1.6mm
θj-a=32.1°C/W
②for SON008V5060
ROHM standard 1 layer board 70x70x1.6mm
θj-a=138.9°C/W
③ IC only
θj-a=195.3°C/W
P  I_OUT ²  R_ON
R_ON  D  R_ONP  1  DR_ONN
②0.90W
1.0
③0.64W
0
Ambient temperature: Ta [°C]
0 25 50 75 100105 125 150
Figure 27. Thermal Derating Curve
(SON008V5060)
If VCC=3.3V, VOUT=1.8V, RONP=0.2Ω, RONN=0.16Ω
IOUT=2A, for example,
D V_OUT /V_CC  1.8 / 3.3  0.545
R_ON  0.545 0.20  1  0.545 0.16
 0.109 0.0728
 0.1818  
Where:
D is the ON duty (=VOUT/VCC).
RONP is the ON resistance of P-channel MOS FET.
RONN is the ON resistance of N-channel MOS FET.
P  2²  0.1818 0.7272 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
12/21
TSZ02201-0J3J0AJ00130-1-2
02.Oct.2014 Rev.002