BD9415FS Datasheet, PDF (13/34 Pages) Rohm – White LED Driver for 4Ch Large LCD Panels (DC/DC converter type)

BD9415FS
3.2.2 LED Current Setting (VREF pin, Sx pin)
First, VREF pin voltage is determined. When performing Analog dimming, be careful of VREF pin input range(0.2 to 2.5V)
and decide typical voltage.
In BD9415FS, LED constant current is controlled by Sx pin voltage as a reference point. Sx pin is controlled to become
one fifth of the voltage of VREF pin voltage. In the case of VREF=1V, it is set to Sx=0.2V.
Therefore, when the resistance to Sx pin versus GND is set to "RS", the relationship between RS, VREF and ILED is as
follows
R_S [ohm] 
V_VREF [V ]
I _LED [ A]  5
3.2.3 LED Short Detection Voltage Setting (LSP terminal)
The voltage of LED short detection can be arbitrarily set up with LSP
pin voltage. It is possible to change the LED short detection voltage,
please input (0.8V to 3.0V) to LSP pin.
About LED short detection voltage, if "VLEDshort" and LSP pin
voltage are set to "VLSP", it is as follows
LSP
COMP ₊
-
REG90=9V
4V
R3
R1
2800k _LSP
R4
1200k
CLSP _R2
3700k LEDx
V_LSP

VLED_SHORT [V ]
6.7
800k
Figure 14. LSP setting example
Since the setting range of a LSP pin is set to 0.8V to 3.0V, VLEDshort can be set up in 5.36V to 20.1V.
○ Equation of setting LSP detect Voltage
When the detection voltage VLSP of LSP is set up by resistance division of R1 and R2 using REG90,
it becomes like the following formula.

R2[k] R4[k] REG90[V ] R3  4[V ] R1[k]

LED_SHORT  _{ (R1[k] R3[k] R2  R4  R2[k] R4[k] R1[k]  R3[k]}  6.7
[V ]　(2)
【Setting example】
Assuming that LSP is approximated by Equation (1) in order to set LSP detection voltage to 6V, R1 comes to 68kΩ. and
R2 comes to 7.6kΩ.
When calculating LSP detection voltage taking into account internal IC resistance by Equation (2), it will be given as:
LED_SHORT


(68[k]

7.6[k] 1200[k]  9[V ]  2800[k]  4[V ]  68[k]
2800[k]  7.6[k]  1200[k]  7.6[k] 1200[k]  68[k]

2800[k]


6.7

6.078[V
]　(2)
*Also including the variation in IC, please also take the part variation in a set into consideration for an actual constant
setup, and inquire enough to it.
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