BD9285F ROHM [Rohm], BD9285F Datasheet - Page 19

• Manufacturer Part Number: BD9285F
• Description: Boost 1channel white LED driver For large LCDs
• Manufacturer: ROHM [Rohm]

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© 2012 ROHM Co., Ltd. All rights reserved.
TSZ22111・15・001
BD9285F
●3.4.5. how to set UVLO
The resistor value can be calculated by the below formula, if the VIN voltage is monitored, and that is divided by the
resistor R1, R2 like the below diagram.
Under voltage lock out pin for the input voltage of the power stage. More than 3.0V(typ.), IC starts boost operation and
stops lower than 2.8V(typ.).
The UVLO pin is high impedance, because the internal resistance to a certain bias is not connected.
○ ○ ○ ○ UVLO detection equality
○ ○ ○ ○ UVLO release equality
[setting example]
By using these R1, R2, the release voltage of UVLO, VINcan can be calculated as following.
So, the bias by the external components is required, even if UVLO function is not used, because the open connection of
this pin is not fixed the potential.
If VIN decreases, R1, R2 value is expressed the following formula by
the VINdet, the detect voltage of UVLO.
By using the R1, R2 in the above equality, the release voltage of UVLO
can be expressed as following.
If the normal input voltage, VIN is 24V, the detect voltage of UVLO is 18V,
R2 is 30k ohm, R1 is calculated as following.
VIN
R
1
CAN
R
VIN
R
[ 2
1
k
3
CAN
[ 0 .
R
]
V
[ 2
(
]
k
VIN
3
0 .
(
]
R
V
DET
[ 1
(
VIN
2
k
[
(
[ 8 .
V
R
R
]
]
[ 2
V
[ 1
DET
k
k
]
R
2
2
R
[
[ 8 .
[ 8 .
V
[ 2
]
]
[ 2
]
V
k
V
k
R
])
]
2
])
[ 2
]
[ 8 .
k
19/36
30
V
3
])
])
[ 0 .
[
k
V
[
[
]
]
V
k
]
(
30
18
]
[
[
k
V
2
]
30
[ 8 .
]
[
Figure 26. UVLO setting example
V
2
k
ON/OFF
163
[ 8 .
]
]
V
[
k
])
TSZ02201-0F1F0C100030-1-2
]
+
-
[
163
V
2.8V/3.0V
]
11.Jul.2012 Rev.001
19
[
k
3 .
UVLO
]
[
CUVLO
V
Datasheet
]
VIN
R1
R2