Design Of Constant Current Driving Chip For Adjustable Light LED By Single-line Transmission

As a recognized fourth-generation light source,LED has the advantages of long aging,high luminous efficiency,green and widely used in the lighting,decoration and display areas.Decorative or display LED mainly has full-color display,adjustable gray scale,constant current drive and other characteristics.With the decorative system continues to increase the scale,improving the accuracy of data transmission,farther transmission distance and low power design become the focus of research.The chip uses a single-wire cascade way to improve the capability of anti-jamming.There is a problem of time and length loss due to data forwarding which seriously reducing the transmission distance.we design a data transfer circuit to ensure the transmission distance length is no longer limited by the number of chip cascade.A new scheme of bit-by-bit separation PWM improve the visual refresh rate and reduce the flashing sense of the display.In addition,the chip integrates a bandgap reference circuit,power-on reset circuit,RC oscillator circuit,linear constant current drive circuit,over-temperature protection circuit,data clock synchronization circuit,all-digital pulse width modulation circuit.Among them,the bandgap reference circuit with curvature compensation has better temperature characteristics;power-on reset circuit ensure its reliability and use low power design;RC oscillator circuit using high-order temperature compensation improves the oscillation frequency stability;drive circuit using linear constant current structure,in which the error amplifier uses a two-stage structure to obtain higher gain and bandwidth,improves the output drive current stability;over-temperature protection circuit can stop the work of the circuit when the temperature is higher than the threshold to protect the chip life;data loss trim circuit,data clock synchronization circuit and pulse width modulation circuit are all digital design.Finally completed the production of the layout.The chip based on the Newtang Technology NUVOTON 0.35?m BCDMOS process,using Cadence Specter and Verilog_XL tools for the overall circuit simulation verification.The working voltage of the chip is 3.3V ~ 6V,the working temperature is-25 ? ~ 120 ?,the standard working current is 17 mA,the current temperature coefficient is 50 ppm,and the power supply voltage regulation rate is 0.18%.When the temperature exceeds 135 ?,the over-temperature protection circuit will stop the chip work.Simulation results show that the chip achieves to compensate the loss of data and design a three-channel 256-level dimming full color display which meets the design expectations.