NCP1060, NCV1060, NCP1063, NCV1063
www.onsemi.com
23
Jittering
OSC
Foldback
SKIP
CS comparator
DRV stage
COMP
S
R
Q
Q
V
COMP(REF)
R
COMP(UP)
I
COMPskip
Figure 41. Skip Cycle Schematic
Ilimit and OPP Function
The function makes the integrated circuit more flexible. The current drawn out of LIM/OPP pin defines the current set point.
Figure 42. Ipk set−point dependence on I
LMOP
current
0
100
200
300
400
500
600
700
800
900
0
50
100
150
200
250
300
350
Current set point [mA]
I
LMOP
[
m
A]
NCP1060
NCP1063
There are several known ways to implement Over Power
Protection (OPP), all suffering from particular problems.
These problems range from the added consumption burden
on the converter or the skip−cycle disturbance brought by
the current−sense offset. A way to reduce the power
capability at high line is to capitalize on the negative voltage
swing present on the auxiliary diode anode. During the
power switch on−time, this point dips to –NV
in
, N being the
turns ratio between the primary winding and the auxiliary
winding. The negative plateau on auxiliary winding will
have an amplitude dependant on the input voltage. Resistors
R
OPPU
and R
OPPL
(Figure 43) define current drawn from
LIM/OPP and the negative voltage on auxiliary winding.
The negative voltage is tied up with bulk voltage, so the
higher the bulk voltage is, the deeper is the negative voltage
on auxiliary winding, the higher current is drawn from
LIM/OPP pin and the lower the peak current is. During the
internal MOSFET off period, voltage on auxiliary winding
is positive, but the IC ignores the LIM/OPP current. The
positive LIM/OPP current has no influence on proper IC
function.
