BD9486F 데이터 시트보기 (PDF) - ROHM Semiconductor

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BD9486F

1ch Boost up type White LED Driver for large LCD

ROHM Semiconductor 

BD9486F

Datasheet

[setting example]

Output voltage = VOUT [V] = 40V

LED total current = IOUT [A] = 0.48V

DCDC input voltage of the power stage = VIN [V] = 24V

Efficiency of DCDC =η[%] = 90%

Averaged input current IIN is calculated as follows.

IIN[A]



VOUT[V]  IOUT[A]

VIN[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.

ΔIL



(VOUT [V]  VIN[V])  VIN[V]

L[H]  VOUT [V]  fSW [Hz]

　

100

(40[V]  24[V])  24[V]

106[H]  40[V]  200 103[Hz]



0.48

[A]

Therefore the inductor peak current, Ipeak is

Ipeak

 IIN[A] 

IL[A] 　[A]

2



0.89[A] 

0.48[ A ]

2

 1.13

[A ] …calculation result of the peak current

If Rcs is assumed to be 0.3Ω

VCS peak  Rcs  Ipeak  0.3[] 1.13[A]  0.339 [V]  0.4V

…Rcs value confirmation

The above condition is met.

And Ipeak_det, the current OCP works, is

Ipeak _ det



0.4[ V ]

0.3[]

 1.33

[A]

If the current rating of the used parts is 2A,

Ipeak  Ipeak _ det  The current rating  1.13[A ]  1.33[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.

IMIN



IIN[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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TSZ02201-0F1F0C100240-1-2

13.Feb.2014 Rev.004

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