BD9394FP Datasheet, PDF (19/31 Pages) Rohm – White LED Driver for large LCD Panels (DCDC Converter type)

BD9394FP, BD9394EFV
Datasheet
【Setting Example】
Output voltage=VOUT[V]=56V
LED total current=IOUT[A]=100mA×4ch=0.40A
DCDC input voltage=VIN[V]=14V
DCDC efficiency=η[%]=90%
Total required average input current IIN:
I
IN
[
A]
=
V_OUT [V ]× I_OUT [ A]
V_IN [V ]×η[%]
　=
56[V ]× 0.40[A]
14[V ]×90[%]
=
1.78
[ A]
When, DCDC switching frequency =fsw[Hz]=200kHz
Inductor L[H]=33uH,
Inductor ripple current ΔIL[A]:
ΔIL
=
(V_OUT [V ] − V_IN [V ]) × V_IN [V ]
L[H ] × V_OUT [V ] × f _SW [Hz ]
　=
(56[V ] − 14[V ]) ×14[V ]
33 ×10 ^−6 [H ] × 56[V ] × 200 × 10 ³[Hz ]
= 1.59
[ A]
Thus, IL peak current Ipeak becomes
Ipeak
=
I _IN [ A] +
∆IL[ A] _{[　A] = 1.78[ A] +} 1.59[ A]
2
2
=
2.58
…Peak current calculation result
[ A]
RCS resistor value when set at 0.1ohm
VCS _peak = Rcs × Ipeak = 0.10[Ω ] × 2.58[ A] = 0.258 [V ] < 0.45V …RCS resistor consideration
and satisfy the condition.
In addition、OCP detection current I_OCP at this time is
I _OCP
=
0.45[V ]
0.1[Ω]
=
4.5
[ A]
If parts used (FET,INDUCTOR、DIODE etc)’s current capacity<5A,
I _peak < I _OCP < ^{Rated current of components}
= 2.58[ A] < 4.5[ A] < 5[ A]
Thus, there is no problem of parts selection as the above condition is satisfied.
In addition、IL ripple current minimum limit Imin is
…DCDC current capacity consideration
Im in
=
I _IN
[ A]
−
∆IL[ A] _{[ A]}
2
=
1.78[ A]
−
0.795[ A]
=
0.985[ A]
>
0　
Thus、will not become discontinuous mode。
To select DC/DC components, give consideration to IC variations as well as individual component variations, and
then conduct thorough verification on practical systems.
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TSZ22111・15・001
19/28
TSZ02201-0F1F0C100180-1-2
09.Nov.2012 Rev.002