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CS5308 データシート(PDF) 11 Page - ON Semiconductor |
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CS5308 データシート(HTML) 11 Page - ON Semiconductor |
11 / 31 page CS5308 http://onsemi.com 11 APPLICATIONS INFORMATION Overview The CS5308 DC/DC controller from ON Semiconductor was developed using the Enhanced V2 topology to meet requirements of low voltage, high current loads with fast transient requirements. Enhanced V2 combines the original V2 topology with peak current−mode control for fast transient response and current sensing capability. The addition of an internal PWM ramp and implementation of fast−feedback directly from VCORE has improved transient response and simplified design. The CS5308 includes VTT monitoring, VTTPGD, PWRGD, and MOSFET gate drivers to provide a “fully integrated solution” to simplify design, minimize circuit board area, and reduce overall system cost. Two advantages of a multi−phase converter over a single−phase converter are current sharing and increased apparent output frequency. Current sharing allows the designer to use less inductance in each phase than would be required in a single−phase converter. The smaller inductor will produce larger ripple currents but the total per phase power dissipation is reduced because the RMS current is lower. Transient response is improved because the control loop will measure and adjust the current faster in a smaller output inductor. Increased apparent output frequency is desirable because the off− time and the ripple voltage of the two−phase converter will be less than that of a single−phase converter. Fixed Frequency Multi−Phase Control In a multi−phase converter, multiple converters are connected in parallel and are switched on at different times. This reduces output current from the individual converters and increases the apparent ripple frequency. Because several converters are connected in parallel, output current can ramp up or down faster than a single converter (with the same value output inductor) and heat is spread among multiple components. The CS5308 controller uses two−phase, fixed frequency, Enhanced V2 architecture to measure and control currents in individual phases. Each phase is delayed 180° from the previous phase. Normally, GATE(H) transitions to a high voltage at the beginning of each oscillator cycle. Inductor current ramps up until the combination of the current sense signal, the internal ramp and the output voltage ripple trip the PWM comparator and bring GATE(H) low. Once GATE(H) goes low, it will remain low until the beginning of the next oscillator cycle. While GATE(H) is high, the Enhanced V2 loop will respond to line and load variations. On the other hand, once GATE(H) is low, the loop can not respond until the beginning of the next PWM cycle. Therefore, constant frequency Enhanced V2 will typically respond to disturbances within the off−time of the converter. The Enhanced V2 architecture measures and adjusts the output current in each phase. An additional input (CSn) for inductor current information has been added to the V2™ loop for each phase as shown in Figure 9. The triangular inductor current is measured differentially across RS, amplified by CSA and summed with the Channel Startup Offset, the Internal Ramp, and the Output Voltage at the non−inverting input of the PWM comparator. The purpose of the Internal Ramp is to compensate for propagation delays in the CS5308. This provides greater design flexibility by allowing smaller external ramps, lower minimum pulse widths, higher frequency operation, and PWM duty cycles above 50% without external slope compensation. As the sum of the inductor current and the internal ramp increase, the voltage on the positive pin of the PWM comparator rises and terminates the PWM cycle. If the inductor starts a cycle with higher current, the PWM cycle will terminate earlier providing negative feedback. The CS5308 provides a CSn input for each phase, but the CSREF and COMP inputs are common to all phases. Current sharing is accomplished by referencing all phases to the same CSREF and COMP pins, so that a phase with a larger current signal will turn off earlier than a phase with a smaller current signal. |
同様の部品番号 - CS5308 |
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同様の説明 - CS5308 |
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