ICE2QR0665_10 INFINEON [Infineon Technologies AG], ICE2QR0665_10 Datasheet - Page 10

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

versus various input bus voltage can be calculated, which is
shown in
Figure 6
According to the typical application circuit, when MOSFET
is turned on, a negative voltage proportional to bus voltage
will be coupled to auxiliary winding. Inside CoolSET
an internal circuit will clamp the voltage on ZC pin to nearly
0V. As a result, the current flowing out from ZC pin can be
calculated as
When this current is higher than I
exceeding this threshold is used to generate an offset to
decrease the maximum limit on V
shown in
CoolSET
maximum output power. Additional advantage to use digital
circuit is the production tolerance is smaller compared to
analog solutions. The typical maximum limit on V
the ZC current is shown in
Figure 7
3.5
At light load condition, the IC enters Active Burst Mode
operation to minimize the power consumption. Details
Version 2.3
I
ZC
0.9
0.8
0.7
0.6
1
0.9
0.8
0.7
0.6
80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400
1
=
300
V
------------------------
R
®
Figure
Figure 6
BUS
ZC1
- Q1 is implemented to get a better control of
Variation of the VCS limit voltage according to
the I
500
Active Burst Mode Operation
V
N
ZC
N
CS-max
6.
P
700
a
current
is a nonlinear one, a digital block in
versus I
900
Figure
1100
Vin(V)
Iz c(uA)
ZC
ZC_1
1300
7.
CS
. Since the ideal curve
, the amount of current
1500
1700
1900
CS
®
versus
- Q1,
2100
[5]
10
about Active Burst Mode operation are explained in the
following paragraphs.
3.5.1
For determination of entering
operation, three conditions apply:
•
•
•
Once all of these conditions are fulfilled, the Active
Burst Mode flip-flop is set and the controller enters
Active Burst Mode operation. This multi-condition
determination for entering Active Burst Mode operation
prevents mistriggering of entering Active Burst Mode
operation, so that the controller enters Active Burst
Mode operation only when the output power is really
low during the preset blanking time.
3.5.2
After entering the Active Burst Mode the feedback
voltage rises as V
inactive PWM section. One comparator observes the
feedback signal if the voltage level V
exceeded. In that case the internal circuit is again
activated by the internal bias to start with swtiching.
Turn-on of the power MOSFET is triggered by the
timer. The PWM generator for Active Burst Mode
operation composes of a timer with a fixed frequency of
50kHz, typically, and an analog comparator. Turn-off is
resulted by comparison of the voltage signal v
internal threshold, by which the voltage across the
shunt resistor V
also be triggered by the maximal duty ratio controller
which sets the maximal duty ratio to 50%. In operation,
the output flip-flop will be reset by one of these signals
which come first.
If the output load is still low, the feedback signal
decreases as the PWM section is operating. When
feedback signal reaches the low threshold V
the internal bias is reset again and the PWM section is
disabled until next time regultaion siganl increases
beyond the V
Mode the feedback signal is changing like a saw tooth
between 3.0V and 3.6V shown in
3.5.3
The feedback voltage immediately increases if there is a high
load jump. This is observed by one comparator. As the
current limit is 34% during Active Burst Mode a certain load
is needed so that feedback voltage can exceed V
After leaving active busrt mode, maximum current can now
be provided to stabilize V
will be set to 1 immediately after leaving Active Burst
the feedback voltage is lower than the threshold of
V
voltage across the shunt resistor is 0.17;
the up/down counter is 7; and
a certain blanking time (t
FBEB
(1.25V). Accordingly, the peak current sense
Entering Active Burst Mode Operation
During Active Burst Mode Operation
Leaving Active Burst Mode Operation
BH
csB
threshold. If working in Active Burst
is 0.34V, accordingly. A turn-off can
OUT
O
starts to decrease due to the
. In addition, the up/down counter
Functional Description
BEB
).
CoolSET
Figure
Active Burst Mode
ICE2QR0665
April 27, 2010
8.
BH
(3.6V) is
LB
1
BL
®
with an
(3.0V),
(4.5V).
- Q1