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BD9483F View Datasheet(PDF) - ROHM Semiconductor

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BD9483F,FV
Datasheet
[setting example]
If DCDC oscillation frequency is 200kHz, we can calculate the RRT as below.
R RT
15000
fsw [kHz]
15000
200[kHz]
75
[k]
3.4.5 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.
UVLO detection equality
As VIN is decreases, R1, R2 value is expressed the following formula by
VIN
the VINdet, the detect voltage of UVLO.
R1
R2[k]
(VIN [V]
DET
2.8[V])
[k]
2.8[V]
UVLO release equality
By using the R1, R2 in the above equality, the release voltage of UVLO can
be expressed as following.
VIN 3.0V(R1[k] R2[k]) [V]
CAN
R2[k]
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
R2[k]
(VIN [V]
DET
2.8[V])
30[k]
(18[V]
2.8[V])
162.9[k]
2.8[V]
2.8[V]
By using these R1, R2, the release voltage of UVLO, VINcan can be calculated too as following.
VINCAN
3.0[V]
R1[k] R2[k]
R2[k]
3.0[V]162.9[k] 30[k][V] 19.29[V]
30[k]
3.4.6 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.
OVP 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 R2[k](VOVPDET[V]3.0[V]) [k]
3.0[V]
Figure 26.
OVP release equality
By using the R1, R2 in the above equality, the release voltage of OVP, VOVPcan can be expressed as following.
VOVP 2.9V(R1[k] R2[k]) [V]
CAN
R2[k]
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© 2012 ROHM Co., Ltd. All rights reserved.
TSZ2211115001
15/29
TSZ02201-0F1F0C100100-1-2
28.Nov.2013 Rev.003
 

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