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FAN102MY Fiches technique(PDF) 10 Page - Fairchild Semiconductor |
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FAN102MY Fiches technique(HTML) 10 Page - Fairchild Semiconductor |
10 / 14 page © 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com FAN102 Rev. 1.0.1 10 Functional Description The proprietary topology of FAN102 enables most simplified circuit design for battery charger applications. Without secondary feedback circuitry, the CV and CC control are achieved accurately. As shown in Figure 24, with the frequency-hopping PWM operation, EMI problems can be solved by using minimized filter components. FAN102 also provides many protection functions. The VDD pin is equipped with over-voltage protection and under-voltage lockout. Pulse-by-pulse current limiting and CC control ensure over-current protection at heavy loads. The GATE output is clamped at 15V to protect the external MOSFET from over- voltage damage. Also, the internal over-temperature- protection function shuts down the controller with latch when overheated. Figure 24. Frequency Hopping Startup Current The startup current is 10µA. Low startup current allows a startup resistor with a high resistance and a low- wattage to supply the startup power for the controller. A 1.5MΩ, 0.25W, startup resistor and a 10µF/25V VDD hold-up capacitor are sufficient for an AC-to-DC power adapter with a wide input range (100VAC to 240VAC) Operating Current The operating current has been reduced to 3.5mA. The low operating current results in higher efficiency and reduces the VDD hold-up capacitance requirement. Once FAN102 enters “deep“ green mode, the operating current is reduced to 1.2mA, which assists the power supply in meeting the power conservation requirements. Green-Mode Operation Figure 25 shows the characteristics of the PWM frequency vs. the output voltage of the error amplifier (VCOMV). The FAN102 uses the positive, proportional, output load parameter (VCOMV) as an indication of the output load for modulating the PWM frequency. In heavy load conditions, the PWM frequency is fixed at 42KHz. Once VCOMV is lower than VN, the PWM frequency starts to linearly decrease from 42KHz to 550Hz, providing further power savings and meeting international power conservation requirements. Figure 25. Green Mode Frequency vs. VCOMV Constant Voltage (CV) and Constant Current (CC) Operation An innovative technique allows the FAN102 to accurately achieve CV / CC characteristic output without secondary-side voltage or current-feedback circuitry. A feedback signal for CV / CC operation from the reflected voltage across the primary auxiliary winding is proportional to secondary winding, so provides the controller the feedback signal from secondary side and achieves constant voltage output property. In constant- current-output operation, this voltage signal is detected and examined by the precise constant current regulation controller, which then determines the on-time of the MOSFET to control input power and provide constant current output property. With feedback voltage VCS across the current-sense resistor, the controller can obtain input power of power supply. Therefore, the region of constant current output operation can be adjusted by the current-sense resistor. Temperature Compensation Built-in temperature compensation provides better constant voltage regulation at different ambient temperatures. This internal compensation current is a positive temperature coefficient (PTC) current that can compensate the forward-voltage drop of the secondary diode of varying with temperature. This variation causes output voltage rising at high temperature. Leading-Edge Blanking (LEB) Each time the power MOSFET switches on, a turn-on spike occurs at the sense resistor. To avoid premature termination of the switching pulse, a leading-edge blanking time is built in. Conventional RC filtering can be omitted. During this blanking period, the current- limit comparator is disabled and cannot switch off the gate driver. |
Numéro de pièce similaire - FAN102MY |
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Description similaire - FAN102MY |
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