ncp1608 ON Semiconductor, ncp1608 Datasheet - Page 20

• Manufacturer Part Number: ncp1608
• Description: Critical Conduction Mode Pfc Controller Utilizing A Transconductance Error Amplifier
• Manufacturer: ON Semiconductor

and rapid operating point changes respectively, while FPP
protects the system against floating feedback pin
Overcurrent Protection (OCP)
inductor peak current and limits the driver on time if the
voltage of the CS pin exceeds V
inductor peak current is programmed by adjusting R
The inductor peak current is calculated using Equation 18:
probability of switching noise inadvertently triggering the
overcurrent limit. This filter blanks out the CS signal for a
duration of t
RC filter is connected between R
DRV
UVP and OVP protect the system from low bulk voltages
The dedicated CS pin of the NCP1608 senses the
An internal LEB filter (Figure 45) reduces the
R
3. FPP Protection: The FB pin is floating. R
sense
pulls down the FB voltage below V
comparator detects an UVP fault and the drive
and error amplifier are disabled.
C
Figure 45. OCP Circuitry with Optional
bulk
LEB
. If additional filtering is necessary, a small
Condition 2
Condition 1
optional
V
External RC Filter
out
I
L(peak)
CS
+
R
R
R
LEB
V
out1
out2
sense
Condition 3
ILIM
sense
C
+
COMP
ILIM
Control
Figure 44. Open Feedback Loop Protection
and the CS pin.
. The maximum
V
ILIM
FB
UVP
+
−
. The UVP
R
OCP
FB
(eq. 18)
FB
http://onsemi.com
sense
+
E/A
+
V
V
V
.
+
+
−
Control
V
OVP
+
−
−
UVP
+
g
REF
20
UVP
m
OVP
conditions. If FPP is not implemented and a manufacturing
error causes the FB pin to float, then V
the coupling within the system and the surrounding
environment. The coupled V
regulation limits (i.e. V
controller to deliver excessive power. The result is that V
increases until a component fails due to the voltage stress.
Shutdown Mode
standby mode of operation. To shutdown the controller, the
FB pin is forced to less than V
for shutdown (Figure 46), the designer must ensure that no
significant leakage current exists in the shutdown circuitry.
Any leakage current affects the output voltage regulation.
Shutdown
The NCP1608 enables the user to set the controller in a
(Enable EA)
Clamp
V
EAH
Figure 46. Shutting Down the PFC Stage
POK
V
out
UVP
R
R
out2
out1
< V
UVP
FB
FB
. When using the FB pin
Fault
< V
may be within the
FB
REF
1
2
3
4
is dependent on
) and cause the
NCP1608
8
7
6
5
out