BD9415FS Datasheet, PDF (18/34 Pages) Rohm – White LED Driver for 4Ch Large LCD Panels (DC/DC converter type)

BD9415FS
【setting example】
Output voltage = VOUT [V] = 40V
LED total current = IOUT [A] = 0.48A
DCDC input voltage of the power stage = VIN [V] = 24V
Efficiency of DCDC=η [%]=90%
Averaged input current IIN is calculated as follows.
I _IN
 ^{VOUT [V ]  IOUT [ A]}
V_IN [V ] [%]

40[V ]  0.48[A]
24[V ]  90[%]
 0.89[A]　
If the switching frequency, fSW = 200kHz, and the inductor, L=100μH, the ripple current of the inductor L (ΔIL [A]) can be
calculated as follows.
IL

(V_OUT [V ] V_IN [V ]) V_IN [V ]
L[H ] V_OUT [V ]  f_SW[Hz]

100
(40[V ] 
10^6[H ] 
24[V
40[V
])  24[A]
]  200 10³[Hz]

0.48[
A]　
Therefore the inductor peak current, IPEAK is
I _PEAK

I_IN [ A] 
IL[A][_{A]  0.89[A] }
2
0.48[ A]
2
 1.13[A]　
…calculation result of the peak current
If RCS is assumed to be 0.3Ω
VCS_PEAK  R_CS  I_PEAK  0.3[] 1.13[A]  0.339[V ]  0.45[V ]
…RCS value confirmation
The above condition is met.
And IPEAK_DET, the current OCP works, is
I _{PEAK _ DET}

0.45[V ]
0.3[]
 1.35[A]
If the current rating of the used parts is 2A,
I_peak  I_{peak _ det}  The current raying  1.33[A] 1.35[A]  2.0[A] …current rating confirmation of DCDC
parts
This inequality meets the above relationship. The parts selection is proper.
And IMIN, the bottom of the IL ripple current, can be calculated as follows.
I _MIN

I_IN [ A] 
IL[ A] _{[ A]}
2
 1.13[A]  0.48[A] 
0.65[A]  0　
This inequality implies that the operation is continuous current mode.
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TSZ22111・15・001
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TSZ02201-0F2F0C100140-1-2
23.May.2016 Rev.001