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LM3410 Arkusz danych(PDF) 8 Page - Texas Instruments |
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LM3410 Arkusz danych(HTML) 8 Page - Texas Instruments |
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8 / 44 page  Control ILED VO Q1 D1 L1 C1 + - VSW IL IC VIN LM3410 SNVS541F – OCTOBER 2007 – REVISED AUGUST 2010 www.ti.com Application Information THEORY OF OPERATION The LM3410 is a constant frequency PWM, boost regulator IC. It delivers a minimum of 2.1A peak switch current. The device operates very similar to a voltage regulated boost converter except that it regulates the output current through LEDs. The current magnitude is set with a series resistor. This series resistor multiplied by the LED current creates the feedback voltage (190 mV) which the converter regulates to. The regulator has a preset switching frequency of either 525 kHz or 1.60 MHz. This high frequency allows the LM3410 to operate with small surface mount capacitors and inductors, resulting in a DC/DC converter that requires a minimum amount of board space. The LM3410 is internally compensated, so it is simple to use, and requires few external components. The LM3410 uses current-mode control to regulate the LED current. The following operating description of the LM3410 will refer to the Simplified Block Diagram (Figure 4) the simplified schematic (Figure 5), and its associated waveforms (Figure 6). The LM3410 supplies a regulated LED current by switching the internal NMOS 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 NMOS control switch. During this on-time, the SW pin voltage (VSW) decreases to approximately GND, 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 sensed 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 diode D1, which forces the SW pin to swing to the output voltage plus the forward voltage (VD) of the diode. The regulator loop adjusts the duty cycle (D) to maintain a regulated LED current. Figure 5. Simplified Boost Topology Schematic 8 Submit Documentation Feedback Copyright © 2007–2010, Texas Instruments Incorporated Product Folder Links: LM3410 |
Podobny numer części - LM3410_14 |
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Podobny opis - LM3410_14 |
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