BD9486F Datasheet, PDF (17/37 Pages) Rohm – 1ch Boost up type White LED Driver for large LCD

BD9486F
Datasheet
●3.2.6 UVLO Setting
Under Voltage Lock Out pin is the input voltage of the power stage. IC starts boost operation if UVLO is more than
3.0V(typ.) and stops if lower than 2.7V(typ.).
The UVLO pin is high impedance, because the internal resistance is not connected to a certain bias.
So, the bias by the external components is required, because the open connection of this pin is not a fixed potential.
Detection voltage is set by dividing resistors R1 and R2. The resistor values can be calculated by the formula below.
○UVLO detection equation
As VIN decreases, R1 and R2 values are set in the following formula by the VIN_DET that UVLO detects.
R1  R2[kΩ]  ^{(VINDET[V]  2.7[V])} [kΩ]
2.7[V]
○UVLO release equation
R1 and R2 setting is decided by the equation above. The equation of UVLO
release voltage is as follows.
VIN_CAN

3.0V

(R1[kΩ]  R2[kΩ])
R2[kΩ]
[V]
【setting example】
If the normal input voltage, VIN is 24V, the detect voltage of UVLO is 18V, R2 is
30kΩ, R1 is calculated as follows.
Figure 26. UVLO setting example
R1  R2[k] ^{(VINDET[V]  2.7[V])}  30[k] ^{(18[V]  2.7[V])}  170.0 [k]
2.7[V]
2.7[V]
By using these R1 and R2, the release voltage of UVLO, VIN_CAN, can be calculated too as follows.
VIN_CAN

3.0[V] 
(R1[k]  R2[k])
R2[k]

3.0[V] 
170[k]  30[k]
30[k]
[V]　
20.0
[V]
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