The Design and Implementation for LED Driver IC Based on Double-frequency OS-PWM Algorithm

A multi-line constant current LED driver chip based on double-frequency OS-PWM algorithm is presented in this paper. The low refresh rate, low gray level color cast, ghost, the first dim line and open road cross problems which are all commonly seen in fine pitch LED display are focused in this chip. The refresh rate is increased by scrambling the display period evenly through OS-PWM algorithm without changing total gray level. The different levels of optimization are provided to achieve uniformity in low gray level. The enough time is left for the capacitor to be discharged to solve the first dim line problem. An open detect module is inbuilt for eliminating open road cross problem. The test results proved that the design of the chip is correct and reasonable.