BD8964FVM-TR Rohm Semiconductor, BD8964FVM-TR Datasheet - Page 9

• 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

●Selection of components externally connected
© 2009 ROHM Co., Ltd. All rights reserved.
BD8964FVM
www.rohm.com
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 better efficiency.
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 BD8964FVM, 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.
The inductor must be selected allowing sufficient margin with which the peak current may not exceed its current rating.
Fig.26 Output capacitor
Fig.27 Input capacitor
If V
I
L
Co≦
Co≦
CC
V
=5V, V
Fig.25 Output ripple current
L=
CC
V
L
T
1m×(2-0.8)
L
CC
SS
IL
L
(5-1.5)×1.5
0.24×5×1M
Cin
×(I
OUT
1.5
limit
V
OUT
=1.5V, f=1MHz, ΔI
Co
-I
OUT
Co
VOUT
ESR
Co
ΔI
)
≒800[μF]
V
V
L
OUT
OUT
=4.375μ → 4.7[μH]
O
・・・(5)
)
L
=0.3×0.8A=0.24A, for example,
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
*Rating of the capacitor should be determined allowing sufficient margin against
output voltage. Less ESR allows reduction in output ripple voltage.
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 (5):
L
OUT
If V
I
< Worst case > I
When Vcc is twice the V
I
: Output ripple current, ESR: Equivalent series resistance of output capacitor)
RMS
RMS
=ΔI
CC
OUT
=I
=0.8×
=5.0V, V
L
OUT
×ESR [V]・・・(4)
=1.5V, 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.
×
Tss: Soft-start time
I
limit
9/13
√
√
OUT
OUT
V
5(5-1.5)
: Over current detection level, 2A(Typ)
RMS(max.)
OUT
=1.5V, and I
ΔI
ΔI
(ΔI
5
=0.8A, and T
L
L
(V
L=
L
V
=
=0.3×I
: Output ripple current, and f: Switching frequency)
CC
CC
OUT
-V
(V
(V
, I
=0.67[A
OUT
OUT
CC
CC
RMS
OUTmax.=
L×V
ΔI
-V
-V
)
max. [A]・・・(2)
SS
L
=
OUT
OUT
×V
=1ms,
CC
[A]・・・(5)
RMS
CC
)×V
)×V
×f
I
OUT
0.8A
2
×f
]
OUT
OUT
[A]・・・(1)
[H]・・・(3)
Technical Note
2009.05 - Rev.A