BD9285F ROHM [Rohm], BD9285F Datasheet - Page 24

• Manufacturer Part Number: BD9285F
• Description: Boost 1channel white LED driver For large LCDs
• Manufacturer: ROHM [Rohm]

Figure 30. the output capacitor circuit
3.5.2. Inductor selection
3.5.3. Output capacitance Cout selection
3.5.4. MOSFET selection
3.5.5. Rectifying diode selection
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TSZ22111・15・001
BD9285F
Figure 29. the waveform and the circuit of
inductor current
I
L
V
IN
* The current exceeding the rated current value of inductor flown through the coil causes magnetic saturation, results
R
Though there is no problem if the absolute maximum rating is larger than the rated current of the inductor L, or is
larger than the sum of the tolerance voltage of C
capacitance (injected charge) needs to be selected to achieve high-speed switching.
* To reduce inductor loss and improve efficiency, inductor with low resistance components (DCR, ACR) needs to be
A schottky barrier diode which has current ability higher than the rated current of L, the reverse voltage larger than the
tolerance voltage of C
L
CS
* Rating of capacitor needs to be selected to have adequate margin against output voltage.
* To use an electrolytic capacitor, adequate margin against allowable current is also necessary. Be aware that the
LED current is larger than the set value transitionally in case that LED is provided with PWM dimming especially .
* One with over current protection setting or higher is recommended.
* The selection of one with small on resistance results in high efficiency.
I
in decreasing in efficiency. Inductor needs to be selected to have such adequate margin that peak current does not
exceed the rated current value of the inductor.
L
selected
V
IN
R
L
CS
R
C
C
V
OUT
ESR
OUT
ΔI
OUT
L
OUT
V
OUT
, and the low forward voltage VF especially needs to be selected.
Output ripple voltage ⊿ V
Output capacitor needs to be selected in consideration of equivalent series
resistance required to even the stable area of output voltage or ripple voltage. Be
aware that set LED current may not be flown due to decrease in LED terminal
voltage if output ripple component is high.
Where
L: the coil inductance [H]
Vin: the input voltage [V]
Iout: the output load current (the summation of LED current) [A]
Iin: the input current [A]
If in the continuous current mode, Please set ⊿ IL to 30% - 50% of the output
load current.
where, R
The inductor value affects the input ripple current. The equality in the section
3.5.1 is as following.
Δ
Δ
Ipeak
V
I
IN
IL
OUT
ESR
OUT
is the equivalent series resistance of Cout.
V
24/36
(
and the rectifying diode V
ILMAX
V
L
OUT
V
I
OUT
[
IN
H
IN
[
[
V
[
]
[
A
V
V
]
]
]
V
]
OUT
OUT
R
I
OUT
V
ESR
is determined by Equation (4):
[%]
IL
IN
[
V
2
[
[
[
V
]
A
A
C
Vout: the DCDC output voltage [V]
Fsw: the oscillation frequency [Hz]
]
])
]
OUT
1
f
SW
[
[
V
A
A
[
IN
]
]
Hz
F
I
[
. The product with small gate
V
OUT
]
]
TSZ02201-0F1F0C100030-1-2
[
A
f
1
SW
]
[
V
]
・・・・・
11.Jul.2012 Rev.001
Datasheet
(4)