Abstract
A low flicker dimmable four-channel LED driver with precise current balancing is proposed in this paper. It is able to achieve highly linear dimming and low lighting flicker at the same time by utilizing a new matrix-style digital pulsewidth modulation (DPWM) along with LED string rotation. Only one LED string needs to be modulated to reduce the total LED current variation and switching loss. To avoid color shift and reduce the effect of subharmonic flicker, a fourth-order common centroid layout is applied to match the current-controlling MOSFETs for precise current balancing. Low-voltage and high-temperature protection circuits as well as a temperature-compensated relaxation oscillator are all integrated to complete the driver design and reduce the overall cost for practical applications. The chip is designed in a TSMC 0.25-μm 1P3M 60-V high-voltage CMOS process with a chip size of 1.76 × 1.37 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The current mismatch among LED strings is measured to be only ±0.28% along with four times reduction in lighting flicker.
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