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LM27341 bảng dữ liệu(PDF) 10 Page - Texas Instruments |
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LM27341 bảng dữ liệu(HTML) 10 Page - Texas Instruments |
10 / 42 page RSENSE PWM Logic Driver Switch 0.15: FB Error Amplifier SYNC Freq. Foldback Amplifier - + VREF 1.0V + - 1.13V - + OVP Comparator - + 0.53V + - Thermal Shutdown Current Limit LDO EN PVIN AVIN BOOST SW L C3 C2 VOUT GND Under Voltage Lockout Corrective Ramp ISENSE Reset Pulse PWM Comparator Error Signal Oscillator Internal Compensation Soft Start + Current Sense Amplifier D2 D1 iL R1 R2 LM27341, LM27342, LM27341Q, LM27342Q SNVS497D – NOVEMBER 2008 – REVISED FEBRUARY 2010 www.ti.com Block Diagram Figure 31. APPLICATION INFORMATION THEORY OF OPERATION The LM27341/LM27342 is a constant-frequency, peak current-mode PWM buck regulator IC that delivers a 1.5 or 2A load current. The regulator has a preset switching frequency of 2 MHz. This high frequency allows the LM27341/LM27342 to operate with small surface mount capacitors and inductors, resulting in a DC-DC converter that requires a minimum amount of board space. The LM27341/LM27342 is internally compensated, which reduces design time, and requires few external components. The following operating description of the LM27341/LM27342 will refer to the Block Diagram (Figure 31) and to the waveforms in Figure 32. The LM27341/LM27342 supplies a regulated output voltage by switching the internal NMOS switch at a constant frequency and varying the duty cycle. A switching cycle begins at the falling edge of the reset pulse generated by the internal oscillator. When this pulse goes low, the output control logic turns on the internal NMOS switch. During this on-time, the SW pin voltage (VSW) swings up to approximately VIN, and the inductor current (iL) increases with a linear slope. The current-sense amplifier measures iL, which generates an output proportional to the switch current typically called the sense signal. The sense signal is summed with the regulator’s corrective ramp and compared to the error amplifier’s output, which is proportional to the difference between the feedback voltage (VFB) and VREF. When the output of the PWM comparator goes high, the switch turns off until the next switching cycle begins. During the switch off-time (tOFF), inductor current discharges through the catch diode D1, which forces the SW pin (VSW) to swing below ground by the forward voltage (VD1) of the catch diode. The regulator loop adjusts the duty cycle (D) to maintain a constant output voltage. 10 Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Links: LM27341 LM27342 LM27341Q LM27342Q |
Số phần tương tự - LM27341_14 |
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Mô tả tương tự - LM27341_14 |
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