Product category:
Power Supply ICs and Controllers
News Release from: Allegro MicroSystems Europe | Subject: A6281
Edited by the Electronicstalk Editorial
Team on 22 October 2007
Driver is bright choice for three-colour
dimming
Three-channel constant-current LED driver IC incorporates an on-chip oscillator for simple programmable brightness control.
New from Allegro MicroSystems Europe, the A6281 is a three-channel constant-current LED driver IC with an on-chip oscillator for simple programmable brightness control The new device is ideally suited to driving clusters of red/green/blue (RGB) LEDs in applications where the cluster forms one pixel in a large display or a lighting fixture
This article was originally published on Electronicstalk on 30 Aug 2000 at 8.00am (UK)
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It precisely controls LED brightness via 10bit pulsewidth modulation (PWM) on each channel, complemented by 7bit analogue current control on each channel to adjust colour balance.
The A6281 drives up to 150mA per channel and operates from a supply voltage of up to 17V, which allows series strings of four or more LEDs to be used on each output.
An on-chip voltage regulator supplies the internal logic and reduces the number of external components and connections.
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Control data are loaded serially, which minimises the number of pins on the device and the package sise.
Only four control signals are needed: clock, serial data, latch and output enable.
These signals are buffered on the chip to drive the next pixel in a daisychained cascade.
An innovative clock regeneration scheme allows large numbers (hundreds, depending on clock frequency and pixel spacing) of devices to be daisychained.
Pixel spacing can range up to 3m.
Output current is programmable in three ways: a single external resistor sets the maximum current that all outputs can drive; three 7bit "dot correction" registers individually set the output currents for the three channels; and three 10bit 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 10bit PWM registers allow a colour depth of 30bit, giving the capability to produce over one billion colours.
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 the LED supply voltage.
Flexible clocking options are available to tailor the device to the application.
To simplify system design, the A6281 can use its internal clock for PWM control and an external clock for loading data; alternatively, the A6281 can use the external data clock as its PWM clock to synchronise pixels at up to 5MHz in larger systems.
Thermal shutdown and undervoltage lockout are provided for self-protection and predictable operation under extreme conditions and faults.
The high level of integration of the new device, coupled with the tiny 3 x 3mm QFN package, allow it to be used in compact board-level designs for applications such as large video displays and signs and architectural and decorative lighting.
The A6281 is available in the extended temperature range of -40 to +85C.
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