ICE2QR0665_10 INFINEON [Infineon Technologies AG], ICE2QR0665_10 Datasheet - Page 7

• Manufacturer Part Number: ICE2QR0665_10
• Description: Off-Line SMPS Quasi-Resonant PWM Controller
• Manufacturer: INFINEON [Infineon Technologies AG]

3
3.1
In ICE2QR0665, a startup cell is integrated into the
depletion CoolMOS
cell consists of a high voltage device and a controller,
whereby the high voltage device is controlled by the
controller. The startup cell provides a pre-charging of
the VCC capacitor till VCC voltage reaches the VCC
turned-on threshold V
operate.
Once the mains input voltage is applied, a rectified
voltage shows across the capacitor C
voltage device provides a current to charge the VCC
capacitor C
certain value, the amplitude of the current through the
high voltage device is only determined by its channel
resistance and can be as high as several mA. After the
VCC voltage is high enough, the controller controls the
high voltage device so that a constant current around
1mA is provided to charge the VCC capacitor further,
until the VCC voltage exceeds the turned-on threshold
V
VCC voltage increase near linearly and the charging
speed is independent of the mains voltage level.
Figure 3
The time taking for the VCC pre-charging can then be
approximately calculated as:
where I
startup cell which is 1.05mA, typically.
Exceeds the VCC voltage the turned-on threshold
V
the IC begins to operate with a soft-start. Due to power
consumption of the IC and the fact that still no energy
from the auxiliary winding to charge the VCC capacitor
before the output voltage is built up, the VCC voltage
drops (Phase II). Once the output voltage is high
enough, the VCC capacitor receives then energy from
the auxiliary winding from the time point t
then will reach a constant value depending on output
load.
Version 2.3
VCCon
VCCon
t
1
=
V
V
V
VCCon
. As shown as the time phase I in Figure 3, the
VCCoff
of at time t
VCC
V
----------------------------------------- -
VCCcharge2
I
VCCon
VCCch
Functional Description
VCC Pre-Charging and Typical
VCC Voltage During Start-up
vcc
VCC voltage at start up
. Before the VCC voltage reaches a
arg
1
, the startup cell is switched off, and
C
is the charging current from the
®
vcc
e2
. As shown in Figure 2, the start
i
VCCon
t1
and the IC begins to
ii
t2
iii
2
bus
on. The VCC
. The high
t
[1]
7
3.2
As shown in
operate with a soft-start. By this soft-start the switching
stresses for the switch, diode and transformer are
minimised. The soft-start implemented in ICE2QR0665
is a digital time-based function. The preset soft-start
time is 12ms with 4 steps. If not limited by other
functions, the peak voltage on CS pin will increase step
by step from 0.32V to 1V finally.
Figure 4
3.3
The PWM controller during normal operation consists of a
digital signal processing circuit including an up/down
counter, a zero-crossing counter (ZC counter) and a
comparator, and an analog circuit including a current
measurement unit and a comparator. The switch-on and -off
time points are each determined by the digital circuit and the
analog circuit, respectively. As input information for the
switch-on determination, the zero-crossing input signal and
the value of the up/down counter are needed, while the
feedback signal V
necessary for the switch-off determination. Details about the
full operation of the PWM controller in normal operation are
illustrated in the following paragraphs.
3.3.1
As mentioned above, the digital signal processing circuit
consists of an up/down counter, a ZC counter and a
comparator. These three parts are key to implement digital
frequency reduction with decreasing load. In addition, a
ringing suppression time controller is implemented to avoid
mistriggering by the high frequency oscillation, when the
output voltage is very low under conditions such as soft start
or output short circuit . Functionality of these parts is
described as in the following.
3.3.1.1
The up/down counter stores the number of the zero crossing
to be ignored before the main power switch is switched on
Vcs_sst
(V)
1.00
0.83
0.66
0.49
0.32
t
on
Soft-start
Normal Operation
Digital Frequency Reduction
Up/down counter
Figure
Maximum current sense voltage during
FB
3
softstart
and the current sensing signal V
4, at the time t
Functional Description
6
CoolSET
9
on
ICE2QR0665
, the IC begins to
April 27, 2010
12
®
Time(ms)
- Q1
CS
are