ice2qr4765z Infineon Technologies Corporation, ice2qr4765z Datasheet - Page 10

• Manufacturer Part Number: ice2qr4765z
• Description: Off-line Smps Quasi-resonant Pwm Controller With Integrated 650v Coolmos And Startup Cell In Dip- 7
• Manufacturer: Infineon Technologies Corporation

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 about
Active Burst Mode operation are explained in the following
paragraphs.
3.5.1
For determination of entering Active Burst Mode 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
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
Version 2.0
I
ZC
the feedback voltage is lower than the threshold of
V
voltage across the shunt resistor is 0.17V;
the up/down counter is 7; and
a certain blanking time (t
0.9
0.8
0.7
0.6
FBEB
1
=
300
V
------------------------
R ZC1 N P
®
(1.25V). Accordingly, the peak current sense
OUT
Figure 6
BUS
-Q1 is implemented to get a better control of
Active
500
Active Burst Mode Operation
Entering Active Burst Mode Operation
During Active Burst Mode Operation
starts to decrease due to the inactive PWM
V
N
CS-max
700
a
is a nonlinear one, a digital block in
Burst
versus I
900
Figure
1100
BEB
Iz c(uA)
Mode
ZC
).
1300
ZC_1
7.
CS
. Since the ideal curve
, the amount of current
1500
operation
1700
1900
CS
prevents
versus
2100
[5]
10
section. One comparator observes the feedback signal if the
voltage level V
internal circuit is again activated by the internal bias to start
with switching.
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 52kHz,
typically, and an analog comparator. Turn-off is resulted by
comparison of the voltage signal v
threshold, by which the voltage across the shunt resistor V
is 0.34V, accordingly. A turn-off can 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 comes 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
reset again and the PWM section is disabled until the next
regulation signal increases beyond the V
Active Burst 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 burst mode, maximum current can now
be provided to stabilize V
Leaving Active Burst Mode Operation
BH
(3.6V) is exceeded. In that case the
O
. In addition, the up/down counter
Functional Description
BL
(3.0V), the internal bias is
CoolSET
ICE2QR4765Z
1
with an internal
BH
May 25, 2011
Figure
threshold. In
LB
®
8.
(4.5V).
- Q1
csB