BD9111NV_14 Datasheet, PDF (12/25 Pages) Rohm – Synchronous Buck Converter with Integrated FET

BD9111NV
Datasheet
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 the conduction losses are the most significant among other dissipations mentioned above, such as gate
charge/discharge dissipation and switching dissipation.
①3.9W
4.0
3.0
2.0
②0.90W
1.0
③0.64W
0
0 25 50 75 100105 125 150
Ambient Temperature: Ta [°C]
Figure 27. Thermal Derating Curve
(SON008V5060)
①for SON008V5060
JEDEC 4 layer board 76.2mmx114.3mmx1.6mm
θj-a=32.1°C/W
②for SON008V5060
ROHM standard 1 layer board 70mmx70mmx1.6mm
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
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
IOUT is the Output current
If VCC=5V, VOUT=3.3V, RONP=0.2Ω, RONN=0.16Ω
IOUT=2A, for example,
D  V_OUT /V_CC  3.3 / 5.0  0.66
R_ON  0.66 0.20  1  0.66 0.16
 0.132  0.0544
 0.1864 
P  2²  0.1864 0.7456 W 
Since RONP is greater than RONN in this IC, the dissipation increases as the ON duty becomes greater. Taking into
consideration the dissipation shown above, thermal design must be carried out with allowable sufficient margin.
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