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LM2832 データシート(PDF) 9 Page - Texas Instruments |
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LM2832 データシート(HTML) 9 Page - Texas Instruments |
9 / 34 page 0 0 VIN VD TON t t Inductor Current D = TON/TSW VSW TOFF TSW IL IPK SW Voltage LM2832 www.ti.com SNVS455A – AUGUST 2006 – REVISED APRIL 2013 APPLICATIONS INFORMATION THEORY OF OPERATION The LM2832 is a constant frequency PWM buck regulator IC that delivers a 2.0A load current. The regulator has a preset switching frequency of 1.6MHz or 3.0MHz. This high frequency allows the LM2832 to operate with small surface mount capacitors and inductors, resulting in a DC/DC converter that requires a minimum amount of board space. The LM2832 is internally compensated, so it is simple to use and requires few external components. The LM2832 uses current-mode control to regulate the output voltage. The following operating description of the LM2832 will refer to the Simplified Block Diagram (Figure 23) and to the waveforms in Figure 24. The LM2832 supplies a regulated output voltage by switching the internal PMOS control switch at constant frequency and variable 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 PMOS control 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. IL is measured by the current sense amplifier, which generates an output proportional to the switch current. 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 and VREF. When the PWM comparator output goes high, the output switch turns off until the next switching cycle begins. During the switch off-time, inductor current discharges through the Schottky catch diode, which forces the SW pin to swing below ground by the forward voltage (VD) of the Schottky catch diode. The regulator loop adjusts the duty cycle (D) to maintain a constant output voltage. Figure 24. Typical Waveforms SOFT-START This function forces VOUT to increase at a controlled rate during start up. During soft-start, the error amplifier’s reference voltage ramps from 0V to its nominal value of 0.6V in approximately 600 µs. This forces the regulator output to ramp up in a controlled fashion, which helps reduce inrush current. OUTPUT OVERVOLTAGE PROTECTION The over-voltage comparator compares the FB pin voltage to a voltage that is 15% higher than the internal reference VREF. Once the FB pin voltage goes 15% above the internal reference, the internal PMOS control switch is turned off, which allows the output voltage to decrease toward regulation. UNDERVOLTAGE LOCKOUT Under-voltage lockout (UVLO) prevents the LM2832 from operating until the input voltage exceeds 2.73V (typ). The UVLO threshold has approximately 430 mV of hysteresis, so the part will operate until VIN drops below 2.3V (typ). Hysteresis prevents the part from turning off during power up if VIN is non-monotonic. Copyright © 2006–2013, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Links: LM2832 |
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同様の説明 - LM2832 |
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