ST ILL010V1 User Manual

Features

STEVAL-ILL010V1

High intensity LED dimming driver evaluation board

based on the L6902

Data Brief

■ Input voltage V

■ Dimming interface

■ Analog current control

■ Average current control by PWM

= 8 V to 30 Vdc

Description

Thanks to their high efficiency and reliability, super high-brightness LEDs are becoming more and more popular as a subsitute for conventional light sources. Although LEDs can be supplied directly from a simple voltage source (like a battery with resistor), for most applications it is better to use a switching current source to achieve not only higher efficiency but also better light output.

This evaluation board is designed around an L6902D-based DC-DC converter with dimming interface. It board implements both of two well known dimming methods:

■ Analog current control

■ Average current control by PWM

While there is only a single dimming input connector on the board, it can be used for both dimming methods.

STEVAL-ILL010V1

The second dimming method implemented on this board is PWM control of average LED current. This control requires a digital PWM signal (with an amplitude of either 3.3 V or 5 V) between the dimming pin and the ground pin. Varying the dutycycle on the board will then change the brightness of the LED (100% = LED off, and 0% = LED fully on).

A signal between 0 and 3.3 V should be used for analog (peak current) dimming. When the dimming pin is grounded (0 V), the 350 mA maximum output current is provided. Likewise, when 3.3 V is applied to the pin, the current provided is zero and the LED is off.

February 2008 Rev 1 1/4

For further information contact your local STMicroelectronics sales office.

www.st.com

Circuit schematic STEVAL-ILL010V1

1 Circuit schematic

Figure 1. Schematic

GND

100uH

Output

Rsense

0.33

Rsense

35V

10uF

35V

9k1

8k2

27k

Dimming Input

L6902D

STPS34OU

OUT

VCC

CS-

CS+

VREF

GND

COMP

220pF

22nF

5k1

CERAMIC

25V

10uF

CERAMIC

25V

3.3V Vref

8 - 24V

2/4

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