A Programmable Current Sink Driver for Multi-String LED Applications

This paper proposes a current sink driver for multi-string LED applications. The driver features high efficiency and high current accuracy. Moreover, this current sink driver topology enables individual brightness control via a digitally programmable resistor bank. In addition, the driver is compatible with a single-bit voltage controller. This paper also presents a clear and concise design procedure suitable for low node processes. To demonstrate the effectiveness of the proposed driver, a three-string LED application is used. Despite the variation in the forward voltage drops among strings, an extremely low current mismatch of 100 $\mu$A is achieved. A worst-case current ripple of less than 1% is demonstrated when a boost converter with 3% output voltage ripple drives the strings. The design example circuitry is simulated using ADS CAD tool utilizing 40 nm CMOS technology.