Constant-current LED driver IC with PWM control

9th March 2007

ES Admin

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The A6280 from Allegro MicroSystems Europe is a new 3-bit constant current LED driver which enables users to minimise the number of components needed to drive LEDs with large pixel spacing. The new driver controls LED luminance using a pulse width modulation (PWM) scheme which gives the application the capability of displaying up to one billion colours. An external resistor is used to set the overall maximum current, which can be set over a wide range from 10 mA to 150 mA per output. An integrated linear regulator allows operation at voltages from 5 to 17V.

Several A6280 devices can be 'daisy chained' together and controlled by four control signals (clock, serial data, latch and output enable). Each of these inputs has buffered outputs on the chip. The input voltage pin can be tied to the LED voltage supply bus, thus eliminating the need for a separate chip

supply bus or an external linear regulator.

Performing PWM control on the outputs controls the LED luminance. The luminance data of the PWM signal for each LED is stored in three 10-bit registers. Each LED can be dot-corrected by a 7-bit scalar register which scales the maximum current from 100% down to 36.5%.

A 31-bit serial shift register loads all the internal latched registers. One bit is used to control whether dot correction/clock divider ratio or luminance data is loaded into the registers. The remaining 30 bits are used for the data. This helps to reduce the pin count of the A6280. To further lower the pin count, the PWM clock and the serial bus clock share the same pin and work concurrently to control LED luminance and to load data.

The A6280 is supplied in a 16-lead dual-inline package (suffix 'A') or a 16-lead MLP package (suffix 'ES').