ICE2QS03G_14 Datasheet, PDF (15/24 Pages) Infineon Technologies AG – Active burst mode for low standby power

Quasi-Resonant PWM controller
ICE2QS03G
Functional Description
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 10.
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,
the up/down counter will be set to 1 immediately after leaving Active Burst Mode. This is helpful to decrease the
output voltage undershoot.
Figure 10 Signals in Active Burst Mode
Data Sheet
15
V2.3, 2014-03-06