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LM2619 bảng dữ liệu(PDF) 8 Page - Texas Instruments |
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LM2619 bảng dữ liệu(HTML) 8 Page - Texas Instruments |
8 / 21 page EAOUT EANEG 1.5V 5k REF SOFT START SGND PVIN VDD EN PGND SYNC/ MODE FB ZERO CROSSING DETECTOR MOSFET CONTROL LOGIC SHUTDOWN CONTROL OSCILLATOR AND MODE CONTROL SW PFM COMP. OVP COMP. PWM COMP. CURRENT SENSE 6 LM2619 SNVS212B – NOVEMBER 2002 – REVISED MAY 2013 www.ti.com 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 SW 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. Figure 21. Simplified Functional Diagram PWM OPERATION While in PWM (Pulse Width Modulation) 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. Energy per cycle is set by modulating the PFET switch on-time pulse-width to control the peak inductor current. This is done by comparing the signal from the current-sense amplifier with a slope compensated error signal from the voltage-feedback error amplifier. At the beginning of each cycle, the clock turns on the PFET switch, causing the inductor current to ramp up. When the current sense signal ramps past the error amplifier signal, the PWM comparator turns off the PFET switch and turns on the NFET synchronous rectifier, ending the first part of the cycle. If an increase in load pulls the output voltage down, the error amplifier output increases, which allows the inductor current to ramp higher before the comparator turns off the PFET. This increases the average current sent to the output and adjusts for the increase in the load. Before going to the PWM comparator, the error signal is summed with a slope compensation ramp from the oscillator for stability of the current feedback loop. During the second part of the cycle, a zero crossing detector turns off the NFET synchronous rectifier if the inductor current ramps to zero. The minimum on time of the PFET in PWM mode is about 200ns. 8 Submit Documentation Feedback Copyright © 2002–2013, Texas Instruments Incorporated Product Folder Links: LM2619 |
Số phần tương tự - LM2619_15 |
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Mô tả tương tự - LM2619_15 |
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