LM3549SQ/NOPB

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An LED driver is an electrical device that regulates power to an LED or a string of LEDs. The LM3549SQ/NOPB is a quiescent-current peak current-mode controller designed for offline application. It is suited for the AC-DC power supplies in isolated and non-isolated applications, featuring wide-range universal input and an adjustable output voltage and current. In this article, we will discuss the applications and working principles of the LM3549SQ/NOPB.

Applications

The LM3549SQ/NOPB offers several advantages in a wide range of applications, such as:

• Driving high-power LED strings in general lighting applications
• Driving line-powered LED lighting systems
• Driving LED strips in LED lighting, display panel backlighting, and decorative lighting applications
• High-efficiency step-down converters, as well as buck and boost converters for telecommunications applications

Working Principle

The LM3549SQ/NOPB uses a peak current control-mode technique to regulate the output current by controlling the duty-cycle. The peak current control method is based on the behavior of a current-mode converter connected to a fixed inductor. The circuitry basically employs a voltage-feedback regulator and a current-feedback regulator, with a duty-cycle modulator. The voltage-feedback and current-feedback regulators monitor and regulate both the output voltage and the inductor current.

The LM3549SQ/NOPB IC is an application-specific integrated circuit (ASIC) that integrates all of the necessary components to achieve the desired performance. It includes a power MOSFET, an inductor, and an output capacitor, as well as the current sense resistors. The power MOSFET regulates the output power based on the duty cycle of the PWM signal. The other components work together to provide an output voltage that is regulated relative to a reference voltage.

The operation of the LM3549SQ/NOPB can be divided into three phases: the on-time phase, the off-time phase, and the soft-start phase. During the on-time phase, the inductor current (IL) increases by a linear rate and the output power is delivered to the load. During the off-time phase, the current level begins to decrease at the same rate. During the soft-start phase, the current level starts to slowly increase, so that it can make the output voltage slowly ramp up to a regulated level.

The LM3549SQ/NOPB provides several other features, such as a built-in over-voltage protection, a programmable hiccup-mode over-current protection, and a programmable auto-restart functionality. These features help to provide a robust system that is reliable and safe to use. In addition, the IC features a wide 4V to 60V operating voltage range, a high switching frequency of up to 1MHz, and a low start-up current of only 10µA.

Conclusion

The LM3549SQ/NOPB is a powerful IC designed to drive high-power LEDs in several different applications, such as general lighting, line-powered LED lighting systems, LED strip lighting, display panel backlighting, and decorative lighting. It utilizes a peak current control-mode technique to regulate the output current, and offers several features, such as over-voltage protection, over-current protection, and auto-restart functionality. The LM3549SQ/NOPB is also suitable for use in high-efficiency step-down converters, as well as buck and boost converters in telecommunications applications.

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