BD9524MUV_10 Datasheet, PDF (12/21 Pages) Rohm – Main Power Supply IC for Note PC (Linear Regulator Integrated)

BD9524MUV
Technical Note
4. MOSFET Selection
VIN
main switch
L
Co
VOUT
Loss on the main MOSFET
Pmain=PRON+PGATE+PTRAN
=
VOUT
VIN
×RON×IOUT²+Ciss×f×VDD+
VIN²Ã—Crss×IOUT×f
IDRIVE
・・・(10)
(Ron: On-resistance of FET; Ciss: FET gate capacitance;
f: Switching frequency Crss: FET inverse transfer function;
I_DRIVE: Gate peak current)
synchronous switch
Loss on the synchronous MOSFET
Psyn=PRON+PGATE
=
VIN-VOUT
VIN
×RON×IOUT²+Ciss×f×VDD ・・・(11)
5. Setting Detection Resistance (Detect ILIMIT at the peak current)
(A) High accuracy current detective circuit (use the low resistance)
VIN
L
R
IL
VOUT
Co
The over current protection function detects the output ripple
current peak value. This parameter (setting value) is
determined as in formula (13) below.
ILMIT= ^65mV(typ) [A]・・・(12)
R
(R: Detection resistance)
OCP
65mV
Current limit
(B) Low loss current detective circuit (use the DCR value of inductor)
VIN
IL
L
RL
r
C
VOUT
Co
When the over current protection is detected by DCR of inductor L,
this parameter (setting value) is determined as in formula (13)
below.
(Application circuit:P18)
ILMIT=65mV(typ)×
r×C
L
[A]・・・(13)
L
OCP
(RL= _r×C )
(RL: the DCR value of inductor)
65mV
Current limit
(C) Low loss current detective circuit (the DCR value of inductor : high)
VIN
IL
L (1-k)RL kRL
R1
R2
C
ILIMIT=
65mV(typ)
k×RL
[A]・・・(14)
VOUT
R2
L
( k= _R1+R2 , _RL = kR1C )
Co
(RL: the DCR value of inductor)
65mV
Current limit
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12/20
2010.03 - Rev.C