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Electronic Components Datasheet Search |
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FSCM0565RI Datasheet(PDF) 12 Page - Fairchild Semiconductor |
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FSCM0565RI Datasheet(HTML) 12 Page - Fairchild Semiconductor |
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12 / 20 page 
FSCM0565R 12 control IC are built in one package. This makes it easy for the control IC to detect the heat generation from the SenseFET. When the temperature exceeds approximately 145 °C, the thermal protection is triggered resulting in shutdown of the FPS. 4. Frequency Modulation: EMI reduction can be accomplished by modulating the switching frequency of a switched power supply. Frequency modulation can reduce EMI by spreading the energy over a wider frequency range than the band width measured by the EMI test equipment. The amount of EMI reduction is directly related to the depth of the reference frequency. As can be seen in Figure 21, the frequency changes from 63KHz to 69KHz in 4ms. Figure 21. Frequency Modulation 5. Soft Start: The FSCM0565R has an internal soft start circuit that increases PWM comparator inverting input voltage together with the SenseFET current slowly after it starts up. The typical soft start time is15ms. The pulse width to the power switching device is progressively increased to establish the correct working conditions for transformers, rectifier diodes and capacitors. The voltage on the output capacitors is progressively increased with the intention of smoothly establishing the required output voltage. Preventing transformer saturation and reducing stress on the secondary diode during start up is also helpful. 6. Burst Operation: To minimize power dissipation in standby mode, the FSCM0565R enters into burst mode operation at light load condition. As the load decreases, the feedback voltage decreases. As shown in Figure 22, the device automatically enters into burst mode when the feedback voltage drops below VBL (300mV). At this point switching stops and the output voltages start to drop at a rate dependent on standby current load. This causes the feedback voltage to rise. Once it passes VBH (500mV), switching resumes. The feedback voltage then falls, and the process repeats. Burst mode operation alternately enables and disables switching of the power SenseFET, thereby reducing switching loss in standby mode. Figure 22. Waveforms of Burst Operation T s T s T s D rain Current f s 66kHz 69kHz 63kHz 4ms t V FB Vds 0.3V 0.5V Ids Vo Voset time Switching disabled T1 T2 T3 Switching disabled T4 |
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