BD9109FVM-TR Rohm Semiconductor, BD9109FVM-TR Datasheet - Page 21

• Manufacturer Part Number: BD9109FVM-TR
• Description: IC REG SW 0.8A 3.3VOUTPUT 8-MSOP
• Manufacturer: Rohm Semiconductor
• Type: Step-Down (Buck)r
• Series: -r

Specifications of BD9109FVM-TR

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 3.3V
• Current - Output: 800mA
• Frequency - Switching: 1MHz
• Voltage - Input: 4.5 ~ 5.5 V
• Operating Temperature: -25°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Power - Output: 587.4mW
• Output Voltage: 3.3 V
• Output Current: 0.8 A
• Input Voltage: 4.5 V to 5.5 V
• Switching Frequency: 1 MHz
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

●Selection of components externally connected
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3. Selection of input capacitor (Cin)
V
1. Selection of inductor (L)
2. Selection of output capacitor (C
CC
* Current exceeding the current rating of the inductor results in magnetic saturation of the inductor, which decreases efficiency.
* Select the inductor of low resistance component (such as DCR and ACR) to minimize dissipation in the inductor for
As the output rise time must be designed to fall within the soft-start time, the capacitance of output capacitor should be
determined with consideration on the requirements of equation (5):
In case of BD9109FVM, for instance, and if V
Inappropriate capacitance may cause problem in startup. A 10 μF to 100 μF ceramic capacitor is recommended.
A low ESR 10μF/10V ceramic capacitor is recommended to reduce ESR dissipation of input capacitor for better efficiency.
Fig.96 Output capacitor
Fig.97 Input capacitor
Co≦
Co≦
better efficiency.
The inductor must be selected allowing sufficient margin with which the peak current may not exceed its current rating.
I
If V
L
CC
L=
V
Fig.95 Output ripple current
=5V, V
CC
T
1m×(2-0.8)
L
V
SS
L
CC
(5-3.3)×3.3
0.24×5×1M
Cin
×(I
IL
L
3.3
OUT
limit
V
OUT
Co
=3.3V, f=1MHz, ΔI
-I
OUT
Co
VOUT
ESR
Co
)
≒364 [μF]
ΔI
V
L
V
OUT
=4.675μ → 4.7[μH]
OUT
O
・・・(5)
)
*Rating of the capacitor should be determined allowing sufficient margin
Output capacitor should be selected with the consideration on the stability region
and the equivalent series resistance required to smooth ripple voltage.
Output ripple voltage is determined by the equation (4)：
ΔV
(ΔI
Input capacitor to select must be a low ESR capacitor of the capacitance
sufficient to cope with high ripple current to prevent high transient voltage. The
ripple current IRMS is given by the equation (6):
against output voltage. Less ESR allows reduction in output ripple voltage.
L
=0.3×0.8A=0.24A, for example,(BD9109FVM)
When VCC is twice the Vout, I
I
< Worst case > I
If V
I
L
OUT
RMS
RMS
: Output ripple current, ESR: Equivalent series resistance of output capacitor)
CC
=ΔI
=I
=0.8×
=5V, V
OUT
OUT
L
×ESR [V]・・・(4)
=3.3V, I
×
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.
OUT
Tss: Soft-start time
I
limit
√
√
21/28
V
3.3(5-3.3)
=3.3V, and I
RMS(max.)
: Over current detection level, 2A(Typ)
OUT
OUT
5
ΔI
(ΔI
ΔI
(V
=0.8A, and T
L
V
L
L=
L
=0.3×I
=
CC
: Output ripple current, and f: Switching frequency)
CC
-V
(V
(V
=0.38[A
OUT
OUTmax.=
OUT
RMS
CC
CC
ΔI
L×V
)
-V
-V
max. [A]・・・(2)
=
L
SS
OUT
OUT
×V
[A]・・・(6)
RMS
CC
I
=1ms,
OUT
0.8A, (BD9109FVM)
CC
2
)×V
)×V
×f
]
×f
OUT
OUT
[H]・・・(3)
[A]・・・(1)
Technical Note
2009.05 - Rev.A