The A6281 is a 3-channel constant-current LED driver with programmable output currents. It is typically used to drive a cluster of red/green/blue (RGB) LEDs for one pixel in a large display or a lighting fixture. Typical applications include large video displays and signs and architectural and decorative lighting. The A6281 drives up to 150 mA per channel and operates from a supply voltage of up to 17 V. Output current is programmable in three ways: (a) a single external resistor sets the maximum current that all outputs can drive; (b) three 7-bit “dot correction” registers individually set the output currents for the three channels; and (c) three 10-bit pulse-width modulation (PWM) registers individually set the duty cycles of the three outputs. The dot correction registers typically adjust output currents to compensate for differences in efficiency of the LEDs on each output and thus tune the white balance of the display. The dot correction registers can also be used to compensate for long-term changes in LED brightness with temperature and aging. The PWM registers typically control the brightness of the LEDs at high refresh rates to display text, graphics and video. The three 10-bit PWM registers allow a color depth of 30 bits (over 1 billion colors).

The maximum supply voltage of 17 volts allows series strings of up to 4 or more LEDs on each output. An on-chip voltage regulator supplies the internal logic and reduces the number of external components and connections.

Control data is loaded serially into a shift register, minimizing the number of pins on the device and the package size. Only four control signals are needed: Clock, Serial Data, Latch, and Output Enable. All these signals are buffered on the chip to drive the next pixel in a daisy-chained cascade. An innovative clock regeneration scheme allows large numbers (hundreds, depending on clock frequency and pixel spacing) of devices to be daisy-chained. Pixel spacing, which depends on clock frequency, can range up to 3 meters (10 feet).

The A6281 is similar to the A6280 and also includes an on-chip PWM clock. The A6280 uses a single external clock both to run the PWM brightness control and to clock data into the device. The A6281 can use its internal clock for PWM control and an external clock for loading data; this set-up can simplify system design. Alternatively, the A6281 can use the external data clock as its PWM clock (like the A6280); this can aid synchronization of large systems.

The A6281 requires only three external components to operate: a resistor to set the maximum output currents and decoupling capacitors for the on-chip voltage regulator and LED supply voltage. The high level of integration and tiny 3 x 3-mm QFN package enable compact board-level designs.