BD9102FVM_13 Datasheet, PDF (15/29 Pages) Rohm – Synchronous Buck Converter Integrated FET

BD9102FVM BD9104FVM
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
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_RMS²  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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