BD9120HFN Rohm, BD9120HFN Datasheet - Page 31

• Manufacturer Part Number: BD9120HFN
• Description: (BD9106FVM - BD9120HFN) Synchronous Buck Converter Integrated FET
• Manufacturer: Rohm

BD9106FVM BD9107FVM BD9109FVM BD9110NV BD9120HFN
© 2012 ROHM Co., Ltd. All rights reserved.
TSZ22111･15･001
●Switching Regulator Efficency
●Consideration on Permissible Dissipation and Heat Generation
www.rohm.com
If V
1000
800
600
400
200
I
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
2)PD(Gate)=Cgs×f×V
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.
As R
OUT
η=
3)PD(SW)=
0
CC
R
0
①587.4mW
②387.5mW
=0.8A, for example,
ON
=5V, V
consideration on the dissipation as above, thermal design must be carried out with sufficient margin allowed.
Fig.93 Thermal derating curve
D=V
V
ONP
P=0.8
=0.66×0.35+(1-0.66)×0.25
=0.231+0.085
2
≒298[mV]
OUT
R)=I
=0.316[Ω]
Vin×Iin
25
Ambient temperature:Ta [℃]
OUT
is greater than R
×I
OUT
OUT
2
OUT
×(0.15+0.316)
RMS
/V
Vin
50
=3.3V, R
2
CC
CC
(MSOP8)
×(R
2
2
×C
×ESR (I
=3.3/5=0.66
①mounted on glass epoxy PCB
②Using an IC alone
×100[%]=
75
θj-a=212.8℃/W
θj-a=322.6℃/W
COIL+
(I
RSS
I
CC
2
DRIVE
85
COIL
[A]：Circuit current.)
(Cgs[F]：Gate capacitance of FET,f[H]：Switching frequency,V[V]：Gate driving voltage of FET)
×I
100
R
OUT
ON
=0.15Ω, R
RMS
) (R
ONN
×f
125
P
[A]：Ripple current of capacitor,ESR[Ω]：Equivalent series resistance.)
OUT
Pin
COIL
in this IC, the dissipation increases as the ON duty becomes greater.
150
[Ω]：DC resistance of inductor, R
ONP
×100[%]=
(C
RSS
=0.35Ω, R
1.0
0.5
1.5
0
[F]：Reverse transfer capacitance of FET、I
0
①1.15W
②0.63W
Fig.94 Thermal derating curve
25
ONN
P
OUT
Ambient temperature:Ta [℃]
P
2
=0.25Ω
OUT
R)
50
31/40
+P
(HSON8)
D
① mounted on glass epoxy PCB
② Using an IC alone
α
www.DataSheet.co.kr
θj-a=133.0℃/W
θj-a=195.3℃/W
75
85
×100[%]
100
ON
[Ω]：ON resistance of FETI
125
P=I
R
D：ON duty (=V
R
R
R
I
OUT
ON
COIL
ONP
ONN
OUT
=D×R
：Output current
150
：ON resistance of P-channel MOS FET
：ON resistance of N-channel MOS FET
：DC resistance of coil
2
×(R
ONP
COIL
0.5
1.5
1.0
0
+(1-D)×R
0
TSZ02201-0J3J0AJ00090-1-2
DRIVE
+R
①0.90W
②0.64W
OUT
D
α as follows:
Fig.95 Thermal derating curve
ON
25
/V
[A]：Peak current of gate.)
)
Ambient temperature:Ta [℃]
CC
ONN
02.MAR.2012 Rev.001
)
(SON008V5060)
50
OUT
① for SON008V5060
② Using an IC alone
[A]：Output current.)
θj-a=138.9℃/W
θj-a=195.3℃/W
ROHM standard 1layer board
75
Datasheet
100
105
With the
125
150
Datasheet pdf - http://www.DataSheet4U.net/