BD9394FP Datasheet, PDF (18/31 Pages) Rohm – White LED Driver for large LCD Panels (DCDC Converter type)

BD9394FP, BD9394EFV
Datasheet
●・OCP Settings/DCDC Components’ Current Capacity Selection Method
One of the function of CS pin - when its pin voltage>0.45 it stops the DCDC. Thus, RCS resistor value
need to be checked after the peak current flow through the inductor is calculated. Furthermore, DCDC external
components’ current capacity needs to be greater than peak current flowing through this inductor.
（Inductor peak current Ipeak calculation method）
Firstly, ripple voltage which occurs at the CS pin is decided depending on the DCDC application conditions.
The conditions when made as below;
Output voltage=VOUT[V]
LED total current=IOUT[A]
DCDC input voltage=VIN[V]
DCDC efficiency =η[%]
Total required average input current IIN:
Inductor
ripple
I _IN =
current
V_OUT [V ]× I_OUT [ A]
IL[^VAI]Nw^[Vhi^]c^×h ^ηoc^[%cu^]rs at
[ A]
inductor
L[H]
during
DCDC drive operation with switching frequency=fsw[Hz] is as follows
ΔIL = ^{(VOUT [V ] − VIN [V ]) × VIN [V ]} [ A]
Therefore, IL’s peak ^Lcu^[Hrre^]n^×t ^VIp_Oe_Ua_Tk^[Vca^]n^×b^fe_SWca^[l^Hcu^zl^]ated using below equation
Ipeak
=
I _IN [ A] +
∆IL[ A]
2
[ A]L(1)
(Resistor RCS connected to CS pin selection method)
This Ipeak flows in RCS and generates voltage. (refer to time chart
diagram on the right). This voltage value, VCSpeak can be calculated as below
VCS _peak = Rcs × Ipeak [V ]
This VCSpeak when reach 0.45V, will stop the DCDC output.
Thus when selecting RCS value, below condition needs to be met.
Rcs[Ω] × Ipeak [ A] < 0.45[V ]
(DCDC Components’ Current Capacity Selection Method)
When OCP reach detection voltage CS=0.45V, Iocp current
I _OCP
=
0.45[V ]
Rcs[Ω]
[ A]L(2)
Ipeak current (1)、I_OCP current (2)、and components’ MAX current capacity needs to satisfy the following
I _peak < I _OCP < ^{Rated current of components}
Above condition needs to be satisfied when selecting DCDC application parts eg. FET, inductor, diode etc.
Furthermore, continuous mode is recommended for normal DCDC applications. Inductor’s ripple current MIN limit value,
lmin becoming
Im
in
=
I _IN
[ A]
−
∆IL[ A] _[
2
A]
>
0
Is a condition to be met. If this is not met, it is called discontinuous mode.
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TSZ22111・15・001
18/28
TSZ02201-0F1F0C100180-1-2
09.Nov.2012 Rev.002