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LM3674 数据表(PDF) 10 Page - Texas Instruments |
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LM3674 数据表(HTML) 10 Page - Texas Instruments |
10 / 26 page VOUT TIME (200 ns/DIV) 200 mA/DIV IL VSW 2V/DIV 10 mV/DIV AC Coupled VIN = 3.6V VOUT = 1.5V IOUT = 400 mA -VOUT L VIN-VOUT L LM3674 SNVS405G – DECEMBER 2005 – REVISED APRIL 2015 www.ti.com 7.3 Feature Description 7.3.1 Circuit Operation During the first portion of each switching cycle, the control block in the LM3674 turns on the internal PFET switch. This allows current to flow from the input through the inductor to the output filter capacitor and load. The inductor limits the current to a ramp with a slope of: (1) by storing energy in a magnetic field. During the second portion of each cycle, the controller turns the PFET switch off, blocking current flow from the input, and then turns the NFET synchronous rectifier on. The inductor draws current from ground through the NFET to the output filter capacitor and load, which ramps the inductor current down with a slope of: (2) The output filter stores charge when the inductor current is high, and releases it when the inductor current is low, smoothing the voltage across the load. The output voltage is regulated by modulating the PFET switch-on time to control the average current sent to the load. The effect is identical to sending a duty-cycle modulated rectangular wave formed by the switch and synchronous rectifier at the SW pin to a low-pass filter formed by the inductor and output filter capacitor. The output voltage is equal to the average voltage at the SW pin. 7.3.2 PWM Operation During PWM operation, the converter operates as a voltage-mode controller with input voltage feed-forward. This allows the converter to achieve excellent load and line regulation. The DC gain of the power stage is proportional to the input voltage. To eliminate this dependence, feed-forward inversely proportional to the input voltage is introduced. While in PWM mode, the output voltage is regulated by switching at a constant frequency and then modulating the energy per cycle to control power to the load. At the beginning of each clock cycle, the PFET switch is turned on and the inductor current ramps up until the comparator trips and the control logic turns off the switch. The current limit comparator can also turn off the switch in case the current limit of the PFET is exceeded. Then the NFET switch is turned on and the inductor current ramps down. The next cycle is initiated by the clock turning off the NFET and turning on the PFET. Figure 18. PWM Operation 10 Submit Documentation Feedback Copyright © 2005–2015, Texas Instruments Incorporated Product Folder Links: LM3674 |
类似零件编号 - LM3674_15 |
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类似说明 - LM3674_15 |
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