The tech-detail-main section includes a detailed description of LED driver applications, particularly focusing on the MAX6972–MAX6975 family of pulse-width modulated (PWM) LED drivers. These drivers are designed for high-speed color and video display boards and support both direct and multiplexed LED driving. Multiplexing allows for more LEDs to be driven with fewer channels, improving efficiency and reducing system costs.
However, improper design of multiplexed LED circuits can lead to unwanted current flows and visual artifacts. This application note explains how these issues arise and provides practical solutions using the MAX6972–MAX6975 drivers. It highlights the importance of managing stray capacitance and ensuring proper discharge paths to prevent flickering or dimming in the display.
A typical multiplexing circuit is illustrated, showing how /MUX0 and /MUX1 control different LED colors via transistors Q1 and Q3. The timing diagram reveals the transition between states, where stray currents can cause problems if not properly managed. The note also discusses the impact of varying forward voltage drops across different colored LEDs, which can affect the performance of the multiplexed system.
To address these issues, resistors R1 and R2 are introduced to provide a discharge path for stray node capacitances, ensuring that the LEDs do not remain forward-biased during transitions. Calculations based on clock frequency and capacitance values help determine the appropriate resistor values for optimal performance. This approach ensures clean transitions and minimizes visible artifacts, making the display system more reliable and visually appealing.
Overall, this document serves as a comprehensive guide for engineers designing multiplexed LED systems, offering insights into best practices and real-world considerations.
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