An Introduction to LM3464 LED Driver with Dynamic Headroom Control
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The document provides an introduction to the LM3464 LED driver chip, including its key features, internal block diagram, application information, and a typical application circuit. The LM3464 has 4 output channels to drive LEDs, wide input voltage range, individual current regulation, and utilizes dynamic headroom control and PWM dimming to maximize efficiency. It also has protections such as overtemperature, undervoltage, and thermal shutdown.
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An Introduction to LM3464 LED Driver with Dynamic Headroom Control
- 5. Application Information Adjusting Voltage Headroom with Resistors Setting LED Current
- 6. Typical Performance Characteristics Effifciency (%) Current Sense Voltage (VSE1) Shutdown Current (EN pin = 0V) Operating Current
- 11. Typical Application Circuit Cascade Operation with Thermal Foldback Control
- 14. LM3464 4 Channel LED Driver Evaluation Board
Notas do Editor
- Welcome to the training module on An Introduction to LM3464 LED Driver with Dynamic Headroom Control
- This training module will introduce LM3464 LED Driver with Dynamic Headroom Control and its application circuit
- The LM3464 is a 4-channel high voltage current regulator that provides a simple solution for LED lighting applications. The LM3464 provides four individual current regulator channels and works in conjunction with external N-channel MOSFETs and sense resistors to give accurate driving current for every LED string. Additionally, the Dynamic Headroom Control (DHC) output can be interfaced to the external power supply to adjust the LED supply voltage to the lowest level that is adequate to maintain all the string currents in regulation, yielding the optimal overall efficiency.
- The operation of the LM3464 upon startup can be divided into several phases according to the change of the rail voltage. The LM3464 is a linear current regulator with four output channels designed for LED lighting systems with wide input voltage range, high speed PWM and thermal foldback dimming control interface. The incorporation of the Dynamic Headroom Control (DHC) technology controls the output voltage of the primary power source and keeps the overall efficiency of the system always maximum. Linear current regulation secures high accuracy output current, LED and system reliability. High speed PWM dimming provides the flexibility of brightness control while maintaining colour temperature of the light. The thermal foldback feature enables the LM3464 to manage the temperature of the LED heat sink or system chassis with a simple NTC/PTC temperature sensor. The thermal foldback input can also be used as an analog dimming control input to adapt to other sensors easily, such as ambient light sensor.
- This page gives application information for defining voltage headroom and setting LED current. The voltage headroom is the rail voltage margin that reserve for precision linear current regulation under steady state. Under steady state, the voltage headroom is always minimized by the LM3464 to reduce power losses on the MOSFETs till one of the drain voltage (VDRx) of the MOSFETs equals the voltage on VDHC pin (0.9V typical). For setting LED current, The LED current regulating mechanism of the LM3464 driver stage contains four individual LED current regulators. Every LED current regulator is composed of an external MOSFET (Q1-Q4), a current sensing resistor (RISNS1-RISNS4) and an amplifier inside the LM3464 that monitors the feedback voltage from the current sensing resistor, The integrated amplifier compares the voltage across current sensing resistors (RISNS1-RISNS4) to a 200mV typical reference voltage and controls the gate voltage of the MOSFETs (Q1-Q4) to realize linear current regulations
- This page shows typical performance characteristics curves taken at VIN = 48V with configuration in typical application for driving twelve power LEDs with four output channels active and output current per channel = 350 mA. TA = 25°C
- Dynamic Headroom Control is a technology that aims at maximizing the overall system efficiency by altering the supply voltage to the LED(s) dynamically in respect to the characteristics of the LED(s). In the LM3464, DHC is facilitated by connecting a resistor in between the OutP pin of the LM3464 and the voltage feedback node of the primary power supply (AC/DC)
- In order to ensure good operation stability of the entire system, the response of the LM3464 circuitry must be set slower than the primary power supply. The response of the LM3464is decided by the value of the capacitor CDHC. In general, a higher capacitance CDHC will result in slower response of the LM3464 driver stage.
- The thermal foldback function of the LM3464 helps in reducing the average LED currents and prolonging the LED lifetime under high temperature. The Thermal pin of the LM3464 is an analog input for thermal foldback control that accepts DC voltage from 0V to VCC.
- The LM3464 provides a DIM pin that accepts TTL logic level signal for PWM dimming. When the DIM pin is pulled low, all LED current regulators will turn off while maintaining VCC regulator and part of the internal circuitries operating. External pull up resistor is required if the DIM pin is driven by open collector / drain driver. The PWM dimming control can coexist with thermal foldback by applying PWM dimming control signal and thermal control signal to the DIM and Thermal pins concurrently.
- The LM3464 can be cascaded to expand the number of output channel. Bases on the master-slave architecture, one of the LM3464 in the system must be set to master mode and the rest must be set to slave mode. This page shows an example application circuit that features eight output channels
- Here is a typical Application Circuit with Fly-Back AC/DC Converter, it shows the circuit of powering the LM3464 LED driver circuitry with an off-the-shelf fly-back AC/ DC converter. In this application, output voltage feedback of the AC/DC converter is mainly governed by a voltage reference IC, LM431 and a voltage divider consists of R1 and R2. The LM3464 influences the output voltage of the AC/DC converter by sinking current from the junction of the voltage divider (R1 and R2) to realize dynamic headroom control.
- When LEDs are connected to the LM3464 driver stage through long cables, the parasitic components of the cable harness and MOSFETS may resonant and eventually lead to unstable system operation. In applications with over 1 meter cables between the LM3464 driver stage and LED light engine, a 4.7kΩ resistor should be added across the GDx pins to GND
- This evaluation board demonstrates the system efficiency and LED current regulation accuracy of the LM3464 LED driver typical application circuit as a 50W LED lighting system. The evaluation board can adapt to different types of primary power supplies with changes of value of a few components only
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