BD9111NV_14 Datasheet, PDF (11/25 Pages) Rohm – Synchronous Buck Converter with Integrated FET

BD9111NV
Datasheet
4. Switching Regulator Efficiency
Efficiency η may be expressed by the equation shown below:
    ^{VOUT  IOUT} 100  ^POUT 100  ^POUT 100
%
V_IN  I_IN
P_IN
P_OUT  Pd
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 ²R)  I_OUT ²  (R_COIL  R_ON )
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)  C_gs  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  IOUT  f}
I _DRIVE
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)  V_IN  I_CC
Where:
ICC is the circuit current.
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