BD9420F Datasheet, PDF (17/31 Pages) Rohm – White LED Driver for large LCD Panels (DCDC Converter Type)

BD9420F
【Setting example】
Output=VOUT[V]=40V
LED 1ch current=120mA, total LED current IOUT[A]=120mA×6ch=0.72A
DCDC input voltage=VIN [V] =24V
DCDC efficiency=η[%]=90%
Mean input current IIN required for the whole system is given by the following equation:
Datasheet
DCDC switching frequency=fsw[Hz]=200kHz
Inductor [H]=33μH
The inductor ripple current ΔIL [A] is given by the following equation:
ΔIL

(V_OUT [V ]  V_IN [V ])  V_IN [V ]
L[H ]  V_OUT [V ]  f _SW [Hz ]
　
(40[V ]  24[V ])  24[V ]
33 10 ^6 [H ]  40[V ]  200 10 ³[Hz ]
 1.45
[ A]
As a result, the peak current Ipeak of IL is given by the following equation.
When RCS resistance is set to 0.1ohm, the VCS peak voltage will be given by the following equation:
Consequently, the result meets the condition.
Furthermore, I_OCP current at which OCP is detected is given by the following equation:
I _OCP

0.4[V ]
0.1[]

4.0
[ A]
So must select the component of about 5A in order to meet the above result.
I _peak  I _OCP  Max. Current tolerance for component
Particularly, To select DC/DC components, give consideration to IC variations as well as individual component
variations, and then conduct thorough verification on practical systems..
The lower limit value of coil ripple current Imin is given by the following equation, the component will not be put into
discontinuous mode.
I min I _IN [ A]
IL[ A] _{[ A] 1.33[ A] 0.73[ A] 0.60[A] 0}
2
※For the selection of DC/DC components, please also consider the inaccuracy of each componentts.
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TSZ22111 • 15 • 001
17/28
TSZ02201-0F1F0C100300-1-2
31.Jan.2014 Rev.002