BD8964FVM_15 Datasheet, PDF (11/25 Pages) Rohm – Synchronous Buck Converter with Integrated FET

BD8964FVM
Datasheet
4. Switching Regulator Efficiency
Efficiency η may be expressed by the equation shown below:

V_OUT
V_IN


I_OUT
I _IN
100
P_OUT
P_IN
100
P_OUT
P_OUT  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  I_OUT ²  R_COIL  R_ON 
Where:
R_COIL is the DC resistance of inductor
R_ON is the ON-Resistance of FET
I_OUT is the Output current
(2) Gate charge/discharge dissipation：Pd(Gate)
Pd Gate  C_gs  f V ²
Where:
C_gs 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

V_IN ²
 C_RSS  I _OUT
I _DRIVE

f
Where:
C_RSS is the reverse transfer capacitance of FET
I_DRIVE is the peak current of gate
(4) ESR dissipation of capacitor：Pd(ESR)
Pd ESR  I _RMS ²  ESR
Where:
I_RMS is the ripple current of capacitor
ESR is the equivalent series resistance
(5) Operating Current Dissipation of IC：Pd(IC)
Pd IC  V_IN  I _CC
Where:
I_CC is the circuit current
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