BD8964FVM-TR Rohm Semiconductor, BD8964FVM-TR Datasheet - Page 8

• Manufacturer Part Number: BD8964FVM-TR
• Description: IC SWITCHING REG W/MOSFET MSOP8
• Manufacturer: Rohm Semiconductor
• Series: -r
• Type: Step-Down (Buck), PWM - Current Moder

Specifications of BD8964FVM-TR

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1 V ~ 1.8 V
• Current - Output: 1.2A
• Frequency - Switching: 1MHz
• Voltage - Input: 4 V ~ 5.5 V
• Operating Temperature: -25°C ~ 85°C
• Mounting Type: *
• Package / Case: *
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

●Switching regulator efficiency
●Consideration on permissible dissipation and heat generation
© 2009 ROHM Co., Ltd. All rights reserved.
BD8964FVM
www.rohm.com
If V
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
current.)
2)PD(Gate)=Cgs×f×V (Cgs[F]：Gate capacitance of FET, f[Hz]：Switching frequency, V[V]：Gate driving voltage of FET)
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
on the dissipation as above, thermal design must be carried out with sufficient margin allowed.
OUT
3)PD(SW)=
η=
P=I
R
D：ON duty (=V
R
R
R
I
OUT
CC
ON
COIL
ONP
ONN
=0.8A, for example,
=5V, V
OUT
ONP
=D×R
V
：Output current
D=V
R
P =0.8
2
：ON resistance of P-channel MOS FET
：ON resistance of N-channel MOS FET
：DC resistance of coil
OUT
R)=I
ON
Vin×Iin
2
×(R
is greater than R
=0.3×0.35+(1-0.3)×0.25
OUT
=0.105+0.175
=0.28[Ω]
≒275.2[mW]
×I
OUT
ONP
OUT
OUT
COIL
Vin
RMS
/V
2
=1.5V, R
×(0.15+0.28)
+(1-D)R
2
CC
×(R
CC
2
+R
2
×C
OUT
×ESR (I
=1.5/5=0.3
×100[%]=
COIL
ON
(I
RSS
I
/V
CC
DRIVE
)
ONN
COIL
CC
+R
×I
[A]：Circuit current.)
OUT
)
ONN
ON
=0.15Ω, R
RMS
) (R
×f
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
ONP
(C
×100[%]=
[Ω]：DC resistance of inductor, R
RSS
=0.35Ω, R
[F]：Reverse transfer capacitance of FET, I
ONN
P
OUT
P
2
=0.25Ω
OUT
R)
8/13
+P
D
α
×100[%]
ON
[Ω]：ON resistance of FET, I
1000
800
600
400
200
0
0
①587.4mW
②387.5mW
25
DRIVE
50
D
Fig. 24
α as follows:
[A]：Peak current of gate.)
①using an IC alone
②mounted on glass epoxy PCB
θj-a=322.6℃/W
θj-a=212.8℃/W
75
85
100
Technical Note
2009.05 - Rev.A
OUT
125
[A]：Output
150