BD9123MUV_14 Datasheet, PDF (14/28 Pages) Rohm – Synchronous Buck Converter with Integrated FET

BD9123MUV
Datasheet
Advantage 3:
(a) Supplied in smaller package due to small-sized power MOS FET incorporated.
・Output capacitor Co required for current mode control: 10µF ceramic capacitor
・Inductor L required for the operating frequency of 1 MHz: 4.7µH inductor
Reduces a Mounting Area Requirement.
VCC
VCC
RPGOOD
CIN
DC/DC
Convertor
RITH
CITH
L
VOUT
CO
L
Co
15mm
RITH
CITH
20mm
Rf Cf
CIN
RPGOOD
Figure 32. Example of Application
5. Switching Regulator Efficiency
Efficiency ŋ may be expressed by the equation shown below:
    ^{VOUT  IOUT} 100  ^POUT 100  ^POUT 100 %
V_IN  L_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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