NCP1060, NCP1063
www.onsemi.com
21
Frequency Foldback
The reduction of no−load standby power associated with
the need for improving the efficiency, requires to change the
traditional fixed−frequency type of operation. This device
implements a switching frequency foldback when the
COMP current passes above a certain level, I
COMPfold
, set
around 68 mA. At this point, the oscillator enters frequency
foldback and reduces its switching frequency.
The internal peak current set−point is following the
COMP current information until its level reaches I
Freeze
.
Below this value, the peak current setpoint is frozen to 30%
of the I
PK(0)
. The only way to further reduce the transmitted
power is to diminish the operating frequency down to F
min
(25 kHz typically). This value is reached at a COMP current
level of I
COMPfold(end)
(100 mA typically). Below this point,
if the output power continues to decrease, the part enters skip
cycle for the best noise−free performance in no−load
conditions. Figure 37 and Figure 38 depict the adopted
scheme for the part.
Figure 37. By observing the current on the COMP pin, the controller reduces its
switching frequency for an improved performance at light load.
0
10
20
30
40
50
60
70
80
90
100
110
50 60 70 80 90 100
Frequency [kHz]
I
COMP
[mA]
NCP1060
NCP1063
Figure 38. Ipk set−point is frozen at lower power demand.
0
100
200
300
400
500
600
700
800
900
40 50 60 70 80 90 100 110
Current set point [mA]
I
COMP
[mA]
NCP1060
NCP1063
