BD9560MUV_10 Datasheet, PDF (11/22 Pages) Rohm – Switching Regulator Controller for Graphic Chip Cores

BD9560MUV
Technical Note
4. MOSFET Selection
VIN
main switch
L
Co
VOUT
synchronous switch
5. Setting Detection Resistance
VIN
L
R
IL
VOUT
Co
Loss on the main MOSFET
Pmain=PRON+PGATE+PTRAN
=
VOUT
VIN
×RON×IOUT²+Ciss×f×VDD+
VIN²Ã—Crss×IOUT×f
IDRIVE
・・・(11)
(Ron: On-resistance of FET; Ciss: FET gate capacity;
f: Switching frequency Crss: FET inverse transfer function;
I_DRIVE: Gate bottom current)
Loss on the synchronous MOSFET
Psyn=PRON+PGATE
= ^{VIN-VOUT ×RON×IOUT2+Ciss×f×VDD} ・・・(12)
VIN
The over current protection function detects the output ripple current
bottom value. This parameter (setting value) is determined as in formula
(13) below.
ILMIT= ^VCL×1/16 [A]・・・(13)
R
(VILIM: ILIM voltage; R: Detection resistance)
Current limit
VIN
IL
L RL
r
C
VOUT
Co
Current limit
6. Setting Load Line Slope
VIN
HG
IL
LG
SS
VDAC
LSP
R1
LSM
R1
Amplifier for setting
Load slope
FB ^R2
When it detect the over current protection from DCR of “the coil L”,
this parameter (setting value) is determined as in formula (14) below.
ILMIT=VCL×1/16× ^r×C
L
[A]・・・(14)
L
(RL= _r×C )
(VCL:CL voltage RL:DCR value of the coil)
RSENSE
VOUT
R2
FB =
×RSENSE×IL+ RSENSE×IL+VOUT
R1
R2
= (1+ _R1 ) × RSENSE×IL+VOUT
So that,
R2
SLOPELL = (1+ _R1 ) × RSENSE
(SLOPELL : Load Line Slope)
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11/21
2010.04 - Rev.C