BD9470AEFV Datasheet, PDF (24/39 Pages) Rohm – White LED driver for medium sized and large sized LCD back light

BD9470AFM・BD9470AEFV
●UVLO setting procedure
UVLO pin for step-up DC/DC power supply. If the UVLO pin voltage reaches 3.0V (Typ.) or more, the IC will start step-up
operation. If it reaches 2.7V (Typ.) or less, the IC will stop the step-up operation.
UVLO pin is the high impedance type and no pull-down resistor inside, resulting in unstable potential in the open-circuit
state. To avoid this problem, be sure to set input voltage with the use of a resistive divider.
While the VIN voltage to be detected is set by the use of resistive dividers R1 and R2 as described below, resistance
setting will be made by the following equation.
○UVLO setting procedure
Assume that VIN is reduced and detected,
UVLO is “VINDET”, R1 and R2 setting will be made by the following equation:
R1 = R2[kΩ]× ^{(VINDET [V ] − 2.7[V ])} [kΩ]　
2.7[V ]
○UVLO release voltage setting equation
When R1 and R2 setting is determined by the equation shown above,
UVLO release voltage will be given by the following equation.
VIN _CAN
=
3.0V
×
(R1[kΩ] + R2[kΩ])
R2[kΩ]
[V ]　
VIN
ON/OFF
+
- ^2.7V/3.0V
R1
UVLO
R2
CUVLO
Figure 28. Block diagram of UVLO
○Setting example
Assuming that the normal VIN operating voltage is 24V, UVLO detection voltage is 18V, and R2 resistance is 30kΩ, R1
resistance setting is made by the following equation
R1 = R2[kΩ]× ^{(VINDET [V ] − 2.7[V ])} = 30[kΩ]× ^{(18[V ] − 2.7[V ])} = 170 [kΩ]
2.7[V ]
2.7[V ]
And, when UVLO release voltage VINCAN setting is made with R1 and R2, it will be given by the following equation
VIN_CAN
=
3.0[V ]×
(R1[kΩ] + R2[kΩ])
R2[kΩ]
= 3.0[V ]× ^{30[kΩ] +170[kΩ][}V ]　= 20
30[kΩ]
[V ]
To select DC/DC components, give consideration to IC variations as well as individual component variations, and then
conduct thorough verification on actual systems.
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TSZ02201-0F10C1002000-1-2
19.Oct.2013 Rev.003