A low power precise current balance LED driver with −0.228% ∼ 0.198% imbalance among three output channels
In this paper, a 3-channel LED driver with precise current balance is proposed. Artful layout topologies instead of complicated circuit structure are created and analyzed to achieve accurate current balance among LED channels with excellent insensitivity to process, temperature and voltage (PVT) variations and small standard deviation for trimming-free bandgap reference voltage. With a high yield rate of 99.5%, the maximum imbalance among LED driving currents for 199 test chips is measured to be merely -0.228% ~ 0.198% which is not only much better than 2% deviation of the conventional one [1] but also very close to the simulated imbalance of -0.18% ~ 0.09% under gradients up to the 2nd-order. In addition, the 1.21V bandgap reference voltage accomplishes a 3σ inaccuracy of 3.78% only. This circuit was fabricated in a Vanguard 0.5μm 5V and 12V 2P3M process with a chip size of 1.25 mm2. Except for the LED driving and setting currents, the power consumption is measured to be 340 μW only.