Datasheet

NCP1028
http://onsemi.com
18
+
-
Vout
+
Vlatch
NTC
V
CC
Q1
Vbulk
Rlower
Rupper
BO
20 ms
RC
To permanent
latch
←
IBO
V
DD
+
-
BO
+
VBO
Figure 31. Adding a comparator on the BO pin offers a way to latch-off the controller.
In Figure 31, Q1 is blocked and does not bother the BO
measurement as long as the NTC and the optocoupler are
not activated. As soon as the secondary optocoupler senses
an OVP condition, or the NTC reacts to a high ambient
temperature, Q1 base is brought to ground and the BO pin
goes up, permanently latching off the controller. Figure 32
depicts the converter behavior in case of total latch-off.
Figure 32. If the BO pin is lifted up to VLATCH, the controller permanently latches off.