CN0410 Small, High Performance LED Driver: A Useful Practical Circuit from ADI

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This article provides a reference design for a programmable 3 channel LED current source driver with isoSPI repeaters.

LED lighting is widely used in industrial applications, but many LEDs are used to obtain sufficient light.

Because of the large size of typical LED drivers, engineers are forced to downsize the LED driver circuit.

The CN 0410 is a reference design for an LED current source driver that allows programmable control of 3 LEDs from 0A to 1A and daisy-chaining via the SPI interface.

This article discusses 4 major features of CN 0410.

1.    3 channels / 1A each LED current source in a small circuit
2.    Low noise current source less than 24μV p-p
3.    Insulated SPI allows multiple boards to be daisy-chained
4.    Easy evaluation by combining with optional boards

CN0410 consists of the following ADI products

AD5686  Small D/A converter with 16 bit, quad and SPI interface
ADA4500-2 10 MHz, 14.5 nV / √ Hz, rail-to-rail input / output, 0 input crossover distortion op-amp
ADP7112 20V, 200 mA low noise linear regulator e 
ADR4520 Ultra-low noise, accurate 2.048V reference voltage
LTC6820 Isolated SPI interface

Below is the block diagram of CN0410.

Since the AD5686 has 4 output channels, 1 D/A converters can control the 3 output channels, which simplifies digital communication and reduces costs.

Also, each channel can be individually programmed to provide current from 0A up to 1A.

The noise characteristic of ADR4520, which provides a reference voltage to AD5686, is very low at 1μV p-p @ 0.1Hz to 10Hz.

The linear regulator ADP7112, which supplies power to the ADR4520, also has low noise of 11μV rms.
In addition, the ADA4500-2 amplifier that buffers the AD5686 output has a noise characteristic of 2μV p-p@0.1Hz to 10Hz.
Due to the superior noise characteristics of these analog ICs, the CN0410 achieves a low noise of less than 24μV p-p at 0.1 to 10Hz.

The communication interface of the CN0410 uses the LTC6820, an isolated SPI controller that can be extended to 100 meters under severe noise conditions.
This SPI interface allows multiple boards to be daisy-chained together.

The LED for evaluating the CN0410 is CFTL-LED-BAR. 
CFTL-LED BAR is a bright, high-lighted red, green, blue 3 color led bar bur for lighting applications.。
The LEDs on the board can be up to 1A, and up to 4 LEDs per 1 color can be used with standard shunts.
(An additional 3V is required for the power supply for each additional LED required for the string, see the product user guide for details)

CN0410 can be connected to a PC using EVAL-ADICUP3029, a form factor development board that supports Arduino and PMOD.

EVAL-ADICUP 3029 and the open source Eclipse-based interactive development environment (IDE) CrossCore Embedded Studio and sample code can run CN0410.

• Industrial / various commercial LED controls
• LED lighting
• Backlight
• Pilot lamp