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SI9140CQ датащи(PDF) 11 Page - Vishay Siliconix |
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SI9140CQ датащи(HTML) 11 Page - Vishay Siliconix |
11 / 15 page Si9140 Vishay Siliconix FaxBack 408-970-5600, request 70026 S-58034—Rev. G, 15-Mar-99 www.siliconix.com 11 FIGURE 4. 1.5-V Converter for GTL+ Bus @ 5 A Figure 4 is a schematic diagram of a converter which produces 1.5 V for a GTL bus. Each of these dc-to-dc converters has four major sections: • PWM Controller-regulates the output voltage • Switch and Synchronous Rectification MOSFETs-delivers the power to the load • Inductor-filters and stores the energy • Input/Output Capacitor-filters the ripple The functions of each circuit are explained in detail below. Design equations are provided to optimize each application circuit. PWM CONTROLLER There are generally two types of controllers, voltage mode or current mode. In voltage mode control, an error voltage is generated by comparing the output voltage to the reference voltage. The error voltage is then compared to an artificial ramp, and the result is the duty cycle necessary to regulate the output voltage. In current mode, an actual inductor current is used, in place of the artificial ramp, to sense the voltage across the current sense resistor. The logic and timing sequence for voltage mode control is shown in Figure 5. The Si9140 offers voltage mode control, which is better suited for applications requiring both fast transient response and high output current. Current mode control requires a current sense resistor to monitor the inductor current. A 10-m Ω sense resistor in a 10-A design will dissipate 1 W, decreasing efficiency by 3.5%. Such a design would require a 2-W resistor to satisfy derating criteria, besides requiring additional board space. Voltage mode control is a second-order LC system and has a faster natural transient response compared to current mode control (first-order RC system). Current mode has the advantage of providing an inherently good line regulation. But the situations where line voltage is fixed, as in the point-of-use conversion for microprocessors, this feature is wasted. Current mode control also provides automatic pulse-to-pulse current limiting. This feature requires a current sense resistor as stated above. These characteristics make voltage mode control ideal for high-end microprocessor power supplies. FIGURE 5. Voltage Mode Logic and Timing Diagram The error amplifier of the PWM controller plays a major role in determining the output voltage, stability, and the transient response of the power supply. In the Si9140, the non-inverting input of the error amplifier is available for use with an external precision reference for tighter tolerance regulation. With a two-pair lead-lag compensation network, it is easy to create a stable 100-kHz closed loop converter with the Si9140 error amplifier. |
Аналогичный номер детали - SI9140CQ |
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Аналогичное описание - SI9140CQ |
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