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BD8964FVM-TR

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

ROHM Semiconductor 

BD8964FVM

Datasheet

4. Switching Regulator Efficiency

Efficiency η may be expressed by the equation shown below:



VOUT

VIN





IOUT

I IN

100

POUT

PIN

100

POUT

POUT  Pd

100

%

Efficiency may be improved by reducing the switching regulator power dissipation factors Pdα as follows:

Dissipation factors:

(1) ON-Resistance dissipation of inductor and FET：Pd(I2R)

  Pd I 2 R  IOUT 2  RCOIL  RON 

Where:

RCOIL is the DC resistance of inductor

RON is the ON-Resistance of FET

IOUT is the Output current

(2) Gate charge/discharge dissipation：Pd(Gate)

Pd Gate  Cgs  f V 2

Where:

Cgs is the gate capacitance of FET

f is the switching frequency

V is the gate driving voltage of FET

(3) Switching dissipation：Pd(SW)

  Pd SW



VIN 2

 CRSS  I OUT

I DRIVE



f

Where:

CRSS is the reverse transfer capacitance of FET

IDRIVE is the peak current of gate

(4) ESR dissipation of capacitor：Pd(ESR)

Pd ESR  I RMS 2  ESR

Where:

IRMS is the ripple current of capacitor

ESR is the equivalent series resistance

(5) Operating Current Dissipation of IC：Pd(IC)

Pd IC  VIN  I CC

Where:

ICC is the circuit current

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22.Jan.2015 Rev.003

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