BD9106FVM Rohm, BD9106FVM Datasheet - Page 11

• Manufacturer Part Number: BD9106FVM
• Description: (BD9102FVM / BD9104FVM / BD9106FVM) Output 1.5A or Less High Efficiency Step-down Switching Regulators
• Manufacturer: Rohm

●Switching regulator efficiency
●Consideration on permissible dissipation and heat generation
© 2009 ROHM Co., Ltd. All rights reserved.
BD9102FVM, BD9104FVM, BD9106FVM
www.rohm.com
Efficiency ŋ may be expressed by the equation shown below:
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
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
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.
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.
If V
As R
on the dissipation as above, thermal design must be carried out with sufficient margin allowed.
η=
OUT
P=I
R
D：ON duty (=V
R
R
R
I
I
R
OUT
OUT
CC
ON
COIL
ONP
ONN
ON
[A]：Output current.)
D=V
P=0.8
ONP
V
OUT
=5V, V
2
=D×R
=0.66×0.35+(1-0.66)×0.25
：Output current
=0.8A, for example,
OUT
=0.231+0.085
=0.316[Ω]
≒298[mV]
Vin×Iin
R)=I
：ON resistance of P-channel MOS FET
：ON resistance of N-channel MOS FET
：DC resistance of coil
OUT
is greater than R
2
×(R
×I
2
×(0.15+0.316)
OUT
OUT
ONP
OUT
/V
Vin
RMS
COIL
CC
2
CC
2
+(1-D)R
×(R
=3.3V, R
×C
2
=3.3/5=0.66
×ESR (I
+R
OUT
×100[%]=
RSS
COIL
(I
I
ON
DRIVE
CC
/V
×I
)
×R
[A]：Circuit current.)
ONN
CC
COIL
OUT
ONN
ON
)
RMS
=0.15Ω, R
×f
) (R
in this IC, the dissipation increases as the ON duty becomes greater. With the consideration
P
[A]：Ripple current of capacitor,ESR[Ω]：Equivalent series resistance.)
Pin
OUT
COIL
(C
×100[%]=
[Ω]：DC resistance of inductor, R
ONP
RSS
=0.35Ω, R
[F]：Reverse transfer capacitance of FET,I
P
OUT
ONN
P
OUT
2
R)
11/17
+P
=0.25Ω
D
α
www.DataSheet.co.kr
×100[%]
ON
[Ω]：ON resistance of FET
1000
800
600
400
200
0
0
①587.4mW
②387.5mW
Fig.49 Thermal derating curves
25
Ambient temperature:Ta [℃]
DRIVE
50
D
α as follows:
[A]：Peak current of gate.)
① using an IC alone
② mounted on glass epoxy PCB
θj-a=322.6 ℃ /W
θj-a=212.8 ℃ /W
75
85
100
Technical Note
2009.05 - Rev.A
125
150
Datasheet pdf - http://www.DataSheet4U.net/