CCM-PFC
ICE3PCS02G
Functional Description
Version 2.0 8 5 May 2010
3 Functional
Description
3.1 General
The ICE3PCS02G is a 8-pins control IC for power
factor correction converters. It is suitable for wide range
line input applications from 85 to 265 VAC with overall
efficiency above 90%. The IC supports converters in
boost topology and it operates in continuous
conduction mode (CCM) with average current con trol.
The IC operates with a cascaded control; the inner
current loop and the outer voltage loop. The inner
current loop of the IC controls the sinusoidal profile for
the average input current. It uses the dependency of
the PWM duty cycle on the line input voltage to
determine th e corresponding input current. This means
the average input current follows the input voltage as
long as the device operates in CCM. Under light load
condition, depending on the choke inductance, the
system may enter into discontinuous conduction mode
(DCM) resulting in a higher harmonics b ut still meeting
the Class D requirement of IEC 1000-3-2.
The outer voltage loop con trols the output bulk voltage,
integrated digitally with in the IC. Depending on the lo ad
condition, internal PI compensation output is converted
to an appropriate DC voltage which controls the
amplitude of the average input current.
The IC is equipped with various protection features to
ensure safe operating condition for both the system
and device.
3.2 Power Supply
An internal under voltage lockout (UVLO) block
monitors the VCC power supply. As soon as it exceeds
12.0V and voltage at pin 6 (VSENSE) >0.5V, the IC
begins operating its gate dr ive and performs its startup
as shown in Figure 3.
If VCC drops below 11V, the IC is off. The IC will then
be consuming typically 1.4mA, whereas consuming
6.4mA during normal operatio n
The IC can be turn ed off and fo rced into st andby mode
by pulling down the voltage at pin 6 (VSENSE) below
0.5V.
Figure 3 State of Operation respect to VCC
3.3 Start-up
During power up when the Vout is less th an 95% of the
rated level, internal voltage loop output increases from
initial voltage under the soft-start control. This results in
a controlled linear increase of the input current from 0A
thus reducing the stress in the external c omponents.
Once Vout has reached 95% of the rated level, the soft-
start control is released to achieve good regulation and
dynamic response in normal operation.
3.4 Frequency Setting and External
Synchronization
The IC can provide external switching frequency
setting by an external resistor RFREQ and the online
synchronization by external pulse signal at FREQ pin.
3.4.1 Frequency Setting
The switching frequency of the PFC converter can be
set with an external resistor RFREQ at FREQ pin as
shown Figure 2. The pin voltage at VFREQ is typical 1V.
The corresponding capacitor for the oscillator is
integrated in the device and the RFREQ/frequency is
given in Figure 4. The recommended operating
frequency range is from 21kHz to 250kHz. As an
example, a RFREQ of 67k at pin FREQ will set a
switching frequency FSW of 65kHz typically.