A 90%-Random Fault Coverage Area-Efficient LED Driver Current Monitor

High-performance linear LED drivers for RGB applications rely on an accurate current generation to achieve the desired luminous intensity or color accuracy. Random hardware faults are a class of malfunctions that can occur during the lifetime of a device, like for example: a bonding failure, an excessive device aging leading to large MOS threshold drift, gate-oxide shorts, etc. For LED drivers, random faults are detected by monitoring the output current. The random fault coverage (RFC), i. e. the percentage of random faults that can be detected by the hardware dedicated to the monitoring function, can be surprisingly low if the current monitor is not specifically designed for this goal. This paper presents a novel current monitor, based on a cascode structure as a sensing element and fabricated in a conventional 180-nm CMOS process, capable of achieving an RFC of 90%. This remarkable result is obtained with an area overhead of only 8.5% with respect to a conventional approach.