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
in
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
4
Circuit schematic STEVAL-ILL010V1
1 Circuit schematic
Figure 1. Schematic
GND
GND
J2
J2
100uH
100uH
Output
Output
2
1
Rsense
0.33
0.33
Rsense
35V
C2
10uF
10uF
35V
C2
+
+
9k1
R1
9k1
R1
1k
1k
R4
R4
R5
8k2
8k2
R5
R6
R6
27k
27k
1k
1k
R3
R3
1
J6
J6
1
J4
Dimming Input
J4
Dimming Input
L1
L1
L6902D
L6902D
U1
U1
D1
D1
1
8
STPS34OU
STPS34OU
OUT
VCC
5
3
2
FB
CS-
CS+
VREF
6
GND
7
COMP
4
220pF
C4
C4
220pF
C3
22nF
C3
22nF
R2
5k1
R2
5k1
CERAMIC
C1
25V
10uF
C1
10uF
CERAMIC
25V
+
+
1
3.3V Vref
J3
J3
3.3V Vref
1
2
J1
J1
8 - 24V
8 - 24V
2/4
STEVAL-ILL010V1 Revision history
2 Revision history
Table 1. Document revision history
Date Revision Changes
11-Feb-2008 1 Initial release.
3/4
STEVAL-ILL010V1
y
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