ncp1652 ON Semiconductor, ncp1652 Datasheet - Page 26

• Manufacturer Part Number: ncp1652
• Description: Power Factor Controllers
• Manufacturer: ON Semiconductor

resistor at the I
between the primary peak and primary average currents.
The gain of the current sense amplifier, A
Equation 5.
during the main switch turn on due to parasitic capacitance
and inductance. This spike may cause incorrect operation of
the PWM Comparator. Filtering the current sense signal will
inevitably change the shape of the current pulse. The
NCP1652 incorporates LEB circuitry to block the first
200 ns (typical) of each current pulse. This removes the
leading edge spikes without altering the current signal
waveform.
and timing capacitor in pF is given by Equation 6.
The gain of the low frequency current buffer is set by the
The current sense signal is prone to leading edge spikes
The relationship between the oscillator frequency in kHz
AVG
pin, R
A
C
CA
T
IAVG
+
C
R
+
T
IAVG
I
AVG
C
47000
. R
RI
T
4k
f
AVG
IAVG
Figure 64. Oscillator Ramp and Control Circuitry
sets the scaling factor
VDD
CA
, is given by
(eq. 5)
(eq. 6)
http://onsemi.com
VDD
+
−
26
x 1.2
+
Oscillator
frequency and the gain of the multiplier. The oscillator ramp
is generated by charging the timing capacitor on the CT Pin,
C
tightly controlled during manufacturing to achieve a
controlled and repeatable oscillator frequency. The current
source turns off and C
pull down transistor once the oscillator ramp reaches its peak
voltage, V
turns off and the charging current source turns on once the
oscillator ramp reaches its valley voltage, V
Figure 64 shows the resulting oscillator ramp and control
circuitry.
frequency, reducing the controller EMI signature and
allowing the use of a smaller EMI filter. The frequency
modulation or jitter is typically ±5% of the oscillator
frequency.
4.0 V / 0.1 V
T
The oscillator controls the switching frequency, f, the jitter
A low frequency oscillator modulates the switching
, with a 200 mA current source. This current source is
CT(peak)
, typically 4.0 V. The pull down transistor
Oscillator
T
To PWM
comparator
To PWM skip
comparator
is immediately discharged with a
CT(valley)
.