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ICE2QS03G Datasheet(PDF) 11 Page - Infineon Technologies AG |
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ICE2QS03G Datasheet(HTML) 11 Page - Infineon Technologies AG |
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11 / 19 page  Quasi-Resonant PWM Controller ICE2QS03G Functional Description Version 2.1 11 February 5, 2010 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 VBL(3.0V), the internal bias is reset again and the PWM section is disabled until next time regultaion siganl increases beyond the VBH threshold. If working in Active Burst Mode the feedback signal is changing like a saw tooth between 3.0V and 3.6V 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 one comparator. As the current limit is 34% during Active Burst Mode a certain load is needed so that feedback voltage can exceed VLB (4.5V). After leaving active busrt mode, maximum current can now be provided to stabilize VO. 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 9 Signals in Active Burst Mode 3.6 Protection Functions The IC provides full protection functions. The following table summarizes these protection functions. Table 2 Protection features During operation, the VCC voltage is continuously monitored. In case of an under- or an over-voltage, the IC is reset and the main power switch is then kept off. After the VCC voltage falls below the threshold VVCCoff, the startup cell is activated. The VCC capacitor is then charged up. Once the voltage exceeds the threshold VVCCon, the IC begins to operate with a new soft-start. In case of open control loop or output over load, the feedback voltage will be pulled up . After a blanking time of 24ms, the IC enters auto-restart mode. The blanking time here enables the converter to provide a high power in case the increase in VFB is due to a sudden load increase. During off-time of the power switch, the voltage at the zero-crossing pin is monitored for output over-voltage detection. If the voltage is higher than the preset threshold vZCOVP, the IC is latched off after the preset blanking time. If the junction temperature of IC exceeds 140 0C, the IC enter into autorestart mode. If the voltage at the current sensing pin is higher than the preset threshold vCSSW during on-time of the power switch, the IC is latched off. This is short-winding protection. During latch-off protection mode, when the VCC voltage drops to 10.5V,the startup cell is activated and the VCC voltage is charged to 18V then the startup cell is shut down again and repeats the previous procedure. There is also a maximum on time limitation inside ICE2QS03G. Once the gate voltage is high longer than tOnMAx, it is turned off immediately. VFBEB VFBBOn VFBLB V FB t VCSB 1.0V VCS VVCCoff V VCC t t VO t VFBBOff Max. Ripple < 1% Blanking Window (tBEB) Current limit level during Active Burst Mode Leaving Active Burst Mode Entering Active Burst Mode VCC Overvoltage Auto Restart Mode VCC Undervoltage Auto Restart Mode Overload/Open Loop Auto Restart Mode Over temperature Auto Restart Mode Output Overvoltage Latched Off Mode Short Winding Latched Off Mode |
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