BD9483F Datasheet, PDF (18/32 Pages) Rohm – White LED Driver for large LCD Panels (DCDC Converter type)

BD9483F,FV
Datasheet
This inequality implies the operation is the continuous current mode.
●3.5.2 Inductor selection
The inductor value affects the input ripple current.
V_IN
I_L
L
ΔIL
V_OUT
ΔIL  ^{(VOUT [V]  VIN [V])  VIN [V]} [A]
L[H]  V_OUT [V]  f_SW [Hz]
I _IN

V_OUT[V] I_OUT[A]
V_IN[V] η[%]
[A]
Ipeak

I _IN [A] 
ΔIL[A]
2
[A]
Where
L: the coil inductance [H]
Vout: the DCDC output voltage [V]
Vin: the input voltage [V]
Iout: the output load current (the summation of LED current) [A]
Iin: the input current [A]
Fsw: the oscillation frequency [Hz]
R_CS
C_OUT
Figure 29.
* The current exceeding the rated current value of inductor flown through the coil causes magnetic saturation, results
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.
* To reduce inductor loss and improve efficiency, inductor with low resistance components (DCR, ACR) needs to be
selected
●3.5.3 Output capacitance Cout selection
V_IN
I_L
L
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.
Output ripple voltage V_OUT is determined by Equation (4):
V_OUT
ΔV_OUT
 ILMAX R _ESR

1
C _OUT

I _OUT
η
¹
f _SW
　[V]　・・・・・
　　(4)
R_ESR
where, R_ESR is the equivalent series resistance of Cout.
R_CS
C_OUT
Figure 30.
* 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.
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