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BD9483F Datasheet, PDF (15/32 Pages) Rohm – White LED Driver for large LCD Panels (DCDC Converter type) | |||
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BD9483F,FV
Datasheet
[setting example]
If DCDC oscillation frequency is 200kHz, we can calculate the RRT as below.
R RT
ï½
15000
fsw [kHz]
ï½
15000
200[kHz]
ï½
75
[kï]
â3.4.5 how to set UVLO
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.
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.
The resistor value can be calculated by the below formula.
âUVLO detection equality
As VIN is decreases, R1, R2 value is expressed the following formula by
VIN
the VINdet, the detect voltage of UVLO.
R1
ï½
R2[kï]
ï´
(VIN [V]
DET
ï
2.8[V])
[kï]
2.8[V]
âUVLO release equality
By using the R1, R2 in the above equality, the release voltage of UVLO can
be expressed as following.
VIN ï½ 3.0Vï´ (R1[kï] ï« R2[kï]) [V]
CAN
R2[kï]
ON/ OFF
+
2.8V/3.0V
-
R1
UVLO
R2
CUVLO
Figure 25.
[setting example]
If the normal input voltage, VIN is 24V, the detect voltage of UVLO is 18V, R2 is 30k ohm, R1 is calculated as following.
R1
ï½
R2[k]ï´
(VIN [V]
DET
ï
2.8[V])
ï½
30[kï]
ï´
(18[V]
ï
2.8[V])
ï½
162.9[kï]
2.8[V]
2.8[V]
By using these R1, R2, the release voltage of UVLO, VINcan can be calculated too as following.
VINCAN
ï½
3.0[V]ï´
R1[kï] ï« R2[kï]
R2[kï]
ï½
3.0[V]ï´ 162.9[kï] ï« 30[kï][V]ãï½ 19.29[V]
30[kï]
â3.4.6 how to set OVP
The OVP terminal is the input for over-voltage protection of output voltage.
The OVP pin is high impedance, because the internal resistance to
a certain bias is not connected.
So, the bias by the external components is required, even if OVP
function is not used, because the open connection of this pin is not
fixed the potential.
The resistor value can be calculated by the below formula.
âOVP detection equality
If the VOUT is boosted abnormally, VOVPdet is the detect voltage of
OVP, R1, R2 can be expressed by the following formula.
OVP
+
- 2.9V/3.0V
VOUT
R1
OVP
R2
COVP
R1 ï½ R2[kï]ï´ (VOVPDET[V]ï 3.0[V]) [kï]
3.0[V]
Figure 26.
âOVP release equality
By using the R1, R2 in the above equality, the release voltage of OVP, VOVPcan can be expressed as following.
VOVP ï½ 2.9Vï´ (R1[kï] ï« R2[kï]) [V]
CAN
R2[kï]
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TSZ02201-0F1F0C100100-1-2
28.Nov.2013 Rev.003
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