BD9130NV_14 Datasheet, PDF (11/25 Pages) Rohm – Synchronous Buck Converter with Integrated FET

BD9130NV
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.
www.rohm.com
© 2012 ROHM Co., Ltd. All rights reserved.
TSZ22111・15・001
11/21
TSZ02201-0J3J0AJ00130-1-2
02.Oct.2014 Rev.002