bd9180gul ROHM Co. Ltd., bd9180gul Datasheet - Page 9

• Manufacturer Part Number: bd9180gul
• Description: 1ch High Efficiency Step-down Switching Regulator
• Manufacturer: ROHM Co. Ltd.

●Switching regulator efficiency
●Consideration on permissible dissipation and heat generation
As R
dissipation as above, thermal design must be carried out with sufficient margin allowed.
As this IC functions with high efficiency without significant heat generation in most applications, no special consideration is
needed on permissible dissipation or heat generation. In case of extreme conditions, however, including lower input voltage,
higher output voltage, heavier load, and/or higher temperature, the permissible dissipation and/or heat generation must be
carefully considered.
Efficiency ŋ may be expressed by the equation shown below:
η=
Efficiency may be improved by reducing the switching regulator power dissipation factors P
Dissipation factors:
1) ON resistance dissipation of inductor and FET：PD(I
2) Gate charge/discharge dissipation：PD(Gate)
3) Switching dissipation：PD(SW)
4) ESR dissipation of capacitor：PD(ESR)
5) Operating current dissipation of IC：PD(IC)
1)PD(I
2)PD(Gate)=Cgs×f×V (Cgs[F]：Gate capacitance of FET,f[H]：Switching frequency,V[V]：Gate driving voltage of FET)
3)PD(SW)=
4)PD(ESR)=I
5)PD(IC)=Vin×I
For dissipation, only conduction losses due to DC resistance of inductor and ON resistance of FET are considered. Because
the conduction losses are considered to play the leading role among other dissipation mentioned above including gate
charge/discharge dissipation and switching dissipation.
ONP
V
1.0
0.8
0.6
0.4
0.2
is greater than R
OUT
2
Vin×Iin
0
R)=I
0
0.51W
×I
OUT
Fig.32 Thermal derating curve
Vin
OUT
RMS
25
If V
2
2
Ambient temperature:Ta [℃]
×(R
CC
×C
2
×ESR (I
CC
×100[%]=
50
I
OUT
COIL
RSS
I
=3.3V, V
(I
(VCSP50L1)
DRIVE
CC
ONN
VCSP50L1(1.1 × 1.6mm □ )
ROHM standard 1 layer board
Board size ： 50mm × 58mm
=0.3A, for example,
×I
R
75
+R
[A]：Circuit current.)
θ j-a=245.0 ℃ /W
ON
D=V
P=0.3
OUT
in this IC, the dissipation increases as the ON duty becomes greater. With the consideration on the
ON
RMS
=0.342+0.215
=0.557[Ω]
=0.57×0.6+(1-0.57)×0.5
OUT
100
) (R
P
×f
OUT
OUT
Pin
[A]：Ripple current of capacitor,ESR[Ω]：Equivalent series resistance.)
2
=1.875V, R
×0.557≒50.13[mW]
/V
125
COIL
CC
×100[%]=
(C
=1.875/3.3=0.57
[Ω] ： DC resistance of inductor, R
RSS
150
[F]：Reverse transfer capacitance of FET,I
ONP
=0.6Ω, R
P
OUT
P
OUT
2
R)
+P
ONN
D
9/14
α
=0.5Ω
×100[%]
P=I
R
D：ON duty (=V
R
R
R
I
OUT
ON
COIL
ONP
ONN
OUT
=D×R
：Output current
ON
：ON resistance of P-channel MOS FET
：ON resistance of N-channel MOS FET
：DC resistance of coil
2
[Ω] ： ON resistance of FET, I
×R
ONP
ON
+(1-D)R
OUT
DRIVE
/V
CC
D
ONN
α as follows:
[A]：Peak current of gate.)
)
OUT
[A] ： Output current.)