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BD8964FVM-TR

4.0V to 5.5V, 1.2A 1ch Synchronous Buck Converter with Integrated FET

ROHM Semiconductor 

BD8964FVM

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 the DC resistance of inductor and ON-Resistance of FET are considered.

This is because conduction losses are most significant among other dissipations mentioned above such as gate

charge/discharge dissipation and switching dissipation.

1000

800

600 ①587.4mW

400 ②387.5mW

200

0

0 25 50 75 85 100 125 150

Ambient Temperature :Ta[°C]

①mounted on glass epoxy PCB

θj-a=212.8°C/W

②using an IC alone

θj-a=322.6°C/W

  P 

RON

IOUDT

2RRONOPN



1 D

RONN

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

Figure 25 Thermal Derating Curve

(MSOP8)

If VCC=5V, VOUT=1.5V, RCOIL=0.15Ω, RONP=0.35Ω, RONN=0.25Ω

IOUT=0.8A, for example,

D=VOUT/VCC=1.5/5=0.3

RON=0.3 x 0.35+(1-0.3) x 0.25

=0.105+0.175

=0.28[Ω]

P=0.82 x (0.15+0.28) ≈ 275.2[mW]

Since RONP is greater than RONN in this IC, the dissipation increases as the ON duty becomes higher. Taking into

consideration the dissipation shown above, thermal design must be carried out with allowable sufficient margin.

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