March 2015

DocID027640 Rev 1

1/6

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STEVAL-ILL071V1

LED backlight demonstration based on the STP04CM05,

ST1S40 and STM32F030

Data brief

Features



24 1-Watt LEDs for ~ 25 W total



Scalable solution capable of cascading

multiple boards for larger systems (pinouts

for connection to other boards)



Preset demo mode for adaptive voltage

control, error representation and brightness

control



Adaptive rail voltage correction for minimal

device dissipation and higher efficiency



All channels monitored and worst-case

corrected



Periodic self-tuning possible



Self-tuning at each startup corrects aging

behavior of LEDs



Double-layered PCB



RoHS compliant

Description

The STEVAL-ILL071V1 demonstrates how to

implement LED backlighting based on the

STP04CM05 high current LED driver, the

ST1S40 step-down DC-DC converter and the

STM32F030 ARM Cortex-M0 microcontroller.

This board features 24 LEDs (8 LED strings with

3 LEDs per string) but additional modules can be

cascaded for a larger backlight area. Possible

application may be extended to any LED lighting

system based on integrated LED drivers. The

design optimizes the LED driver rail voltage such

that dissipation within the driver is minimized. It

employs an adaptive process to compensate for

aging effects of the LEDs (forward LED voltage

increases with time). This is achieved by tracking

the drop across the LED string using the ADC of

the STM32F030, and acting accordingly on the

feedback pin of the ST1S40 (via PWM) to adjust

rail voltage until the LED driver comes out of

constant current mode. This knee point of

operation is detected and the DC-DC converter

output is locked to the minimum voltage at which

the LED driver is able to maintain constant

current operation. This ensures minimum drop

across the driver channels and thus minimum

loss within them, improving efficiency, reducing

power comsumption and increasing reliability.