BD9479FV ROHM [Rohm], BD9479FV Datasheet - Page 18

• 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
● ● ● ● OCP setting / DCDC component current tolerance selection guide
voltage becomes larger than 0.4V.Consequently, it is needed to calculate a peak current flowing through the coil L and then
review the resistance of RCS.Furthermore, a current tolerance for DC/DC components should be larger than that for peak
current flowing through the coil L.The following describes the peak coil current calculation procedure, CS pin connection
resistor RCS selection procedure, and DC/DC component current tolerance selection procedure .
○ ○ ○ ○ Peak coil current Ipeak calculation
for DC/DC application components first, Assuming the conditions as
below:
by the following equation.
equation.
○ ○ ○ ○ CS pin connection resistor RCS selection procedure
stop.Consequently, to select RCS resistance, the following condition
should be met.
○ ○ ○ ○ DC/DC component current tolerance selection procedure
The relation among Ipeak current (Equation (1)), Iocp current (Equation (2)), and Maximum current tolerance for
component should meet the following equation.
frequency fsw [Hz], inductor ripple current ∆IL [A] generated at
(or H) is given by the following equation.
timing chart shown to the right）The voltage VCSpeak is given by the
following equation.
Iocp current needed for OCP detection voltage CS to reach 0.4V is given by the following equation:
The OCP detection function that is one of the functions of the CS pin will stop the DC/DC converter operating ifthe CS pin
Ripple voltage generated at the CS pin is determined by conditions
And then mean input current IIN required for the whole system is given
As a result, the peak current Ipeak of IL is given by the following
If
Further, according to drive operation with the DC/DC converter switching
The current Ipeak flows into RCS to generate voltage.（See the
「output voltage=VOUT[V] 」
「LED total current=IOUT[A] 」
「DCDC input voltage=VIN[V] 」
「DCDC efficiency=η[%] 」
VCSpeak
Δ
Rcs
VCS
I
Ipeak
IL
IN
I
voltage
OCP
peak
V
(
I
V
L
Ipeak
OUT
peak
V
OUT
[
H
IN
I
[
IN
V
]
[
Rcs
Rcs
[
. 0
V
V
[
]
[ 4
]
V
]
[
A
reaches
V
[
I
OUT
V
]
I
OCP
OUT
V
]
Ipeak
]
[%]
]
IN
[
V
[
[
V
IL
A
]
. 0
[
2
A
]
])
[
[ 4
]
f
A
MAX current tolerance
L
SW
0.4V,
[
[V
]
V
V
A
(
[
IN
]
]
]
) 2
Hz
[
[
V
A
]
]
]
L
DC/DC
[
) 1 (
A
]
18/26
output
the inductor L
will
VIN
PGND
TSZ02201-0F1F0C100020-1-2
CS
N
fsw
IL
L
Rcs
9.Aug.2012 Rev.001
VOUT
Datasheet