BD8966FVM-TR Rohm Semiconductor, BD8966FVM-TR Datasheet - Page 9

• Manufacturer Part Number: BD8966FVM-TR
• Description: IC SWITCHING REG W/MOSFET MSOP8
• Manufacturer: Rohm Semiconductor
• Series: -r
• Type: Step-Down (Buck), PWM - Current Moder

Specifications of BD8966FVM-TR

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1 V ~ 2.5 V
• Current - Output: 800mA
• 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

●Consideration on permissible dissipation and heat generation
●Selection of components externally connected
© 2010 ROHM Co., Ltd. All rights reserved.
BD8966FVM
www.rohm.com
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.
P=I
R
D:ON duty (=V
R
R
R
I
If V
As R
on the dissipation as above, thermal design must be carried out with sufficient margin allowed.
1. Selection of inductor (L)
OUT
ON
COIL
ONP
ONN
I
I
* Current exceeding the current rating of the inductor results in magnetic saturation of the inductor, which decreases
* Select the inductor of low resistance component (such as DCR and ACR) to minimize dissipation in the inductor for
L
OUT
OUT
CC
=D×R
:Output current
D=V
R
P =0.8
efficiency.
The inductor must be selected allowing sufficient margin with which the peak current may not exceed its current rating.
If V
better efficiency.
ONP
:ON resistance of P-channel MOS FET
:ON resistance of N-channel MOS FET
:DC resistance of coil
=5V, V
ON
=0.8A, for example,
=0.105+0.175
=0.28[Ω]
≒275.2[mW]
2
Fig.25 Output ripple current
×(R
CC
=0.3×0.35+(1-0.3)×0.25
OUT
is greater than R
V
=5V, V
L=
2
CC
ONP
×(0.15+0.28)
OUT
COIL
/V
IL
L
OUT
CC
+(1-D)R
=1.5V, R
(5-1.5)×1.5
0.24×5×1M
+R
OUT
=1.5/5=0.3
/V
ON
CC
=1.5V, f=1MHz, ΔI
Co
)
VOUT
ONN
)
ΔI
COIL
L
ONN
=0.15Ω, R
in this IC, the dissipation increases as the ON duty becomes greater. With the consideration
=4.375μ → 4.7[μH]
ONP
L
=0.3×0.8A=0.24A, for example,
=0.35Ω, R
The inductance significantly depends on output ripple current.
As seen in the equation (1), the ripple current decreases as the
inductor and/or switching frequency increases.
Appropriate ripple current at output should be 30% more or less of
the maximum output current.
ONN
9/14
=0.25Ω
ΔI
ΔI
(ΔI
L
L
L=
L
=
=0.3×I
: Output ripple current, and f: Switching frequency)
(V
(V
OUT
CC
CC
L×V
ΔI
-V
-V
max. [A]・・・(2)
1000
800
600
400
200
L
OUT
OUT
×V
CC
0
0
CC
①587.4mW
②387.5mW
)×V
)×V
×f
×f
OUT
OUT
25
50
①using an IC alone
②mounted on glass epoxy PCB
θj-a=322.6℃/W
θj-a=212.8℃/W
[A]・・・(1)
[H]・・・(3)
Fig. 24
75
85
100
Technical Note
2010.04 - Rev.B
125
150