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BD9489F Datasheet, PDF (22/39 Pages) Rohm – DCDC converter with current mode | |||
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BD9489F
Datasheet
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]
ï½
VOUT[V] ï´ IOUT[A]
VIN[V] ï´ ï¨[%]
ãï½
40[V] ï´ 0.48[A]
24[V] ï´ 90[%]
ï½
0.89
[A]
If the switching frequency, fSW = 200kHz, and the inductor, L=100μH, the ripple current of the inductor L (ÎIL[A]) can be
calculated as follows.
ÎIL
ï½
(VOUT [V] ï VIN[V]) ï´ VIN[V]
L[H] ï´ VOUT [V] ï´ fSW [Hz]
ãï½
100
(40[V] ï 24[V]) ï´ 24[V]
ï´10ï6[H] ï´ 40[V] ï´ 200 ï´103[Hz]
ï½
0.48
[A]
Therefore the inductor peak current, Ipeak is
Ipeak
ï½ IIN[A] ï«
ïIL[A] ã[A]
2
ï½
0.89[A] ï«
0.48[ A ]
2
ï½ 1.13
[A ] â¦calculation result of the peak current
If Rcs is assumed to be 0.3â¦
VCS peak ï½ Rcs ï´ Ipeak ï½ 0.3[ï] ï´1.13[A] ï½ 0.339 [V] ï¼ï¼ 0.4V
â¦Rcs value confirmation
The above condition is met.
And Ipeak_det, the current OCP works, is
Ipeak _ det
ï½
0.4[ V ]
0.3[ï]
ï½ 1.33
[A]
If the current rating of the used parts is 2A,
Ipeak ï¼ï¼ Ipeak _ det ï¼ï¼ The current rating ï½ 1.13[A ] ï¼ï¼ 1.33[A ] ï¼ï¼ 2.0[A ] â¦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
ï½
IIN[A] ï
ïIL[A] [A]
2
ï½
1.13[A] ï
0.48[ A ]
ï½
0.65[ A ]
ï¾ï¾
0
This inequality implies that the operation is continuous current mode.
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TSZ22111ã»15ã»001
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TSZ02201-0F1F0C100250-1-2
29.Oct 2014 Rev.002
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