BD91361MUV_14 Datasheet, PDF (13/27 Pages) Rohm – Synchronous Buck Converter with Integrated FET

BD91361MUV
Datasheet
5. 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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