BD9479FV ROHM [Rohm], BD9479FV Datasheet - Page 20

• Manufacturer Part Number: BD9479FV
• Description: White LED Driver for large LCD Panels (DCDC Converter type)
• Manufacturer: ROHM [Rohm]

www.rohm.com
© 2012 ROHM Co., Ltd. All rights reserved.
TSZ22111・15・001
BD9479FV
● ● ● ● Selection of inductor L
● ● ● ● Selection of output capacitor C
I
L
I
L
V
IN
Select an inductor with an adequate margin so that peak current will not exceed the rated current of the inductor.
※ If a current in excess of the rated current of the inductor applies to the coil, the inductor will cause magnetic
※ To reduce power dissipation from and increase efficiency of inductor, select an inductor with low resistance
※ Select capacitor ratings with an adequate margin for output voltage.
※ To use an electrolytic capacitor, an adequate margin should be provided for permissible current. Particularly to
R
V
L
CS
IN
R
L
saturation, resulting in efficiency degradation.
component (DCR or ACR).
CS
apply PWM light modulation to LED, note that a current higher than the set LED current transiently flows.
C
OUT
ΔI
L
V
C
R
OUT
V
OUT
ESR
OUT
OUT
Expressing efficiency as shown by Equation (2), peak input current is given as
Equation (3).
Here,
Basically, make setting of ∆IL to approximately 30% to 50% of the output load
current.
IL
Δ
Δ
shown by Equation (1), the larger the inductor and the higher the switching
frequency, the inductor ripple current ∆IL becomes increasingly lower.
Select a capacitor on the output side taking into account the stability region
of output voltage and equivalent series resistance necessary to smooth
ripple voltage. Note that higher output ripple voltage may result in a drop in
LED pin voltage, making it impossible to supply set LED current.
The output ripple voltage ∆V
Here, R
MAX
The value of inductor has significant influence on the input ripple current. As
V
V
IL
V
OUT
OUT
L：Inductor value[H]
V
I
IN
IN
IN
I
：input current[A]
：input voltage[V]
IN
ESR
(
V
I
I
20/26
L
ILMAX
OUT
OUT
IN
Δ
Equivalent series resistance of C
V
2
IL
・・・・・
OUT
V
IN
V
R
)
OUT
ESR
V
f
SW
IN
V
IN
I
C
OUT
[
OUT
OUT
1
A
V
I
F
OUT
SW
OUT
]
・・・・・
is given by Equation (4).
：output total current[A]
：Oscillation frequency[Hz]
：DC/DC output voltage[V]
I
OUT
Δ
TSZ02201-0F1F0C100020-1-2
2
(2)
IL
f
1
SW
・・・・・
OUT
[
V
]
.
・・・・・
9.Aug.2012 Rev.001
(1)
Datasheet
(3)
(4)