ICE2QR0665G_14 Datasheet, PDF (14/27 Pages) Infineon Technologies AG – Off-Line SMPS Quasi-Resonant PWM Controller with integrated 650V CoolMOS? and startup cell in DSO-16/12

CoolSET™Q1
ICE2QR0665G
Functional Description
Figure 8 V_CS-max versus I_ZC
3.5
Active Burst Mode Operation
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 Entering Active Burst Mode Operation
For determination of entering Active Burst Mode operation, three conditions apply:
 the feedback voltage is lower than the threshold of V_FBEB (1.25V). Accordingly, the peak current sense
voltage across the shunt resistor is 0.17V;
 the up/down counter is N_{ZC_ABM} (7) and
 a certain blanking time t_BEB (24ms).
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 mis-
triggering 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 During Active Burst Mode Operation
After entering the Active Burst Mode the feedback voltage rises as V_OUT starts to decrease due to the inactive
PWM section. One comparator observes the feedback signal if the voltage level V_FBBOn (3.6V) is exceeded. In
that case the 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 f_sB (52kHz, typical) and an analog comparator. Turn-off is resulted
if the voltage across the shunt resistor at CS pin hits the threshold V_csB (0.34V). A turn-off can also be triggered
if the duty ratio exceeds the maximal duty ratio D_maxB (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_FBBOff (3.0V), the internal bias is reset again and the PWM section is disabled
until next time regulation signal increases beyond the V_FBBOn (3.6V) threshold. If working in Active Burst Mode
the feedback signal is changing like a saw tooth between V_FBBOff and V_FBBOn shown in Figure 9.
3.5.3 Leaving Active Burst Mode Operation
The feedback voltage immediately increases if there is a high load jump. This is observed by a comparator. As
the current limit is 34% during Active Burst Mode a certain load is needed so that feedback voltage can exceed
V_FBLB (4.5V). After leaving active burst mode, maximum current can now be provided to stabilize V_O. In addition,
Data Sheet
14
V2.1, 2014-04-01