ICE2QS03G_14 Datasheet, PDF (14/24 Pages) Infineon Technologies AG – Active burst mode for low standby power

Quasi-Resonant PWM controller
ICE2QS03G
Functional Description
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 ICE2QS03G, 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_{ZC_FS}, the amount of current exceeding this threshold is used to
generate an offset to decrease the maximum limit on V_CS. Since the ideal curve shown in Figure 8 is a
nonlinear one, a digital block in ICE2QS03G is implemented to get a better control of 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_CS versus the ZC current is shown in
Figure 9.
Figure 9 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.
Data Sheet
14
V2.3, 2014-03-06