ST STEVAL-ILL009V1 Application Note
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ST STEVAL-ILL009V1 Application Note

ST STEVAL-ILL009V1 Application Note

Generating multicolor light using rgb leds
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Introduction
The new high power and brightness RGB LEDs are going to be used in many different
lighting applications as backlighting, general lighting systems, traffic signals, automotive
lighting, advertising signs, etc. They are becoming popular mainly because it is possible to
generate an easy multicolor light with special lighting effects and their brightness can be
easy changed. On top of this, their long lifetime and small size make them the light source of
the future.
This document describes how to drive RGB LEDs, how to calculate a power dissipation,
how to design an over temperature protection, how to use a software PWM modulation and
why over voltage protection should be implemented for this kind of application.
STEVAL-ILL009V1 reference board shown in
demonstrate this design concept. This board was designed for driving super high brightness
multicolor RGB LEDs with current up to 700 mA per LED. The LED brightness and color can
be very easy changed by potentiometers and an automatic color change mode continuously
modulates the color of the LED to generate multicolor light. The LED over temperature
protection is designed on this board and therefore the power delivered to the LED can be
automatically limited to prevent LED overheating.
The STEVAL-ILL009V1 is a mother board assembled without LEDs. To evaluate light effect
features, it is necessary to order a load board (additional board with assembled RGB LEDs).
Two load boards are available for easy performance evaluation. The first one with the
®
OSTAR
ILL009V3 and the second one with the Golden DRAGON
point 2) has ordering code STEVAL-ILL009V4. All technical information about these
reference boards such as bill of materials, schematics, software, temperature protection and
so on are described in the sections below.
Note:
A new reference board STEVAL-ILL009V5 was designed in order to replace the former
STEVAL-ILL009V1. The main reason why the new board was developed is to demonstrate
a new DC/DC converter capabilities using the ST1S10 and new improved LED drivers
STP04CM05 and STP08CP05. Thanks to the ST1S10 the size of the inductor is extremely
decreased, efficiency improved and board size significantly reduced. The STEVAL-
ILL009V5 reference design is described in
Figure 1.
September 2008
Generating multicolor light using RGB LEDs
Projection Module (refer to
STEVAL-ILL009V1 reference board
Application note
Figure 1
was developed in order to
Chapter
12, point 1) has ordering code STEVAL-
®
Chapter
9.
Rev 2
AN2531
LEDs (refer to
Chapter
12,
1/40
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Summary of Contents for ST STEVAL-ILL009V1

  • Page 1: Figure 1. Steval-Ill009V1 Reference Board

    LED can be automatically limited to prevent LED overheating. The STEVAL-ILL009V1 is a mother board assembled without LEDs. To evaluate light effect features, it is necessary to order a load board (additional board with assembled RGB LEDs).

  • Page 2: Table Of Contents

    LED temperature protection ........16 STEVAL-ILL009V1 reference board ......17 General description .
  • Page 3 AN2531 Contents STEVAL-ILL009V4 load board ....... . 36 11.1 Schematic description ........37 11.2 Bill of material .
  • Page 4 BOM - STEVAL-ILL009V1 ........
  • Page 5 Figure 13. STEVAL-ILL009V1 power sources schematic ........21 Figure 14.

  • Page 6: Driving Concept For Rgb Leds

    Driving concept for RGB LEDs AN2531 Driving concept for RGB LEDs RGB refers to the three primary colors, red, green, and blue. Different colors can be generated by controlling the power to each LED. In this application, the microcontroller provides three software PWM signals (principle is described below in Chapter 4) for LED drivers STP04CM596 so the color can be regulated.

  • Page 7: How To Drive Many Leds

    AN2531 How to drive many LEDs How to drive many LEDs In several applications not only one RGB LED, but many of them must be driven. There are at least two possible ways to drive many RGB LEDs using the STP04CM596 LED driver, depending on the specific lighting application.

  • Page 8: Figure 4. Led Driver Connection - Parallel Configuration

    How to drive many LEDs AN2531 Figure 4. LED driver connection - parallel configuration Micro STP04CM596 STP04CM596 Parallel connection Control Control logic logic part part LED supply voltage AM00287 8/40...

  • Page 9: How To Set High Current For Leds

    HB LEDs available on the market. For example, this principle is also used in the STEVAL-ILL009V1 presented in this application note, because the board has maximum current capability of 700 mA (2 channels x 350 mA).

  • Page 10: Color Control - Software Modulation

    Color control - software modulation AN2531 Color control - software modulation Software control modulation allows adjusting power to each channel of the STP04CM596 driver (i.e. LED brightness). Figure 6 explains the principle showing an example of how to set an 8% duty cycle for red, 28% duty cycle for blue, 6% duty cycle for green and 98% duty cycle for a fourth LED.
  • Page 11 AN2531 Color control - software modulation 100 Hz and above it is not detected by the human eye and is considered as a stable light. Using Equation 1 Equation 2, the resolution can be obtained as shown in Equation Equation 1 SW_PWM SW_PWM Equation 2...

  • Page 12: Power Dissipation

    Power dissipation AN2531 Power dissipation The maximum power dissipation can be calculated with ambient temperature and thermal resistance of the chip. The thermal resistance depends on the type of package and can be found together with maximum junction temperature in the datasheet. The maximum allowable power consumption without a heatsink is calculated as follows: Equation 6 –...

  • Page 13: Figure 7. Rgb Led Configuration

    AN2531 Power dissipation Figure 7. RGB LED configuration STP04CM596 R ext I-REG V f_red V f_blue V f_green V f_green AM00290 Note: Red, blue and green LEDs have different forward voltages (refer to Chapter 2). In general, the red LED has a lower forward voltage and therefore the power dissipation on the red LED channel is the highest.

  • Page 14: Over Voltage Protection

    Over voltage protection AN2531 Over voltage protection Description The maximum voltage on the output channels of STP04CM596 is 16 V. Any wire or PCB track connection between LEDs and STP04CM596 driver presents a parasitic inductance as shown in Figure 8. This parasitic inductance produces voltage spikes on the outputs of the driver when the driver is turning off the LEDs and it can be dangerous for the STP04CM596 as it can exceed the maximum output voltage rating.

  • Page 15: Type Of Solutions

    AN2531 Over voltage protection Type of solutions Figure 9 shows possible types of over voltage protection. The first solution proposes a Transil™ or a Zener diode connected between each channel of the LED driver and ground. Unidirectional Transils with break down voltage lower than 16 V such as the SMAJ Transil family (refer to Chapter 12, point 5) can be used.

  • Page 16: Led Temperature Protection

    LED temperature protection AN2531 LED temperature protection The STEVAL-009V1 was designed for high power RGB LEDs with a nominal power even higher then ten watts. As the lifetime of LEDs significantly decreases with temperature, the proper temperature management must be implemented to check and limit its maximum values.

  • Page 17: Steval-Ill009V1 Reference Board

    Over temperature signalization connector for SW evaluation and change. General description Figure 11 shows components position on the STEVAL-ILL009V1. On the left side there is DC/DC converter with L4973D3.3 (ref. to Chapter 12, point 6) with power capability 3 A at 4 V.

  • Page 18: Getting Started

    Figure 11. Components position on the STEVAL-ILL009V1 Getting started Getting started chapter briefly describes how to use the STEVAL-ILL009V1 as a step by step guide in order to quickly start with the evaluation. Connect LED board to the STEVAL-ILL009V1 reference board using the 30-pin load connector2.

  • Page 19: Schematic Description

    Schematic description The STEVAL-ILL009V1 reference board schematic diagram is shown in Figure 12 Figure 13.

  • Page 20: Figure 12. Steval-Ill009V1 Schematics - Led Drivers Part

    STEVAL-ILL009V1 reference board AN2531 Figure 12. STEVAL-ILL009V1 schematics - LED drivers part 20/40...

  • Page 21: Figure 13. Steval-Ill009V1 Power Sources Schematic

    AN2531 STEVAL-ILL009V1 reference board Figure 13. STEVAL-ILL009V1 power sources schematic 21/40...

  • Page 22: Bill Of Material

    STEVAL-ILL009V1 reference board AN2531 Bill of material Table 1. BOM - STEVAL-ILL009V1 Item Qty Reference Part Note Ordering code CONNECTOR1 10 PIN CONNECTOR2 30 PIN C1, C6 10 nF Ceramic SMD1206 C2, C3, C4, C5, C7, C8, C9, C11, C12,...

  • Page 23: Design Calculation

    AN2531 STEVAL-ILL009V1 reference board Design calculation 8.5.1 LED supply voltage In order to have low power dissipation on STP04CM596 LED drivers it was chosen to have LED supply voltage 4 V. The maximum current flowing through LEDs is 2.8 A (0.35 A x 8).

  • Page 24: Table 2. Temperature Limit Setting Using Stlm20

    Table Note: The software implemented in the STEVAL-ILL009V1 sets the integer number to 65. This means that the temperature is limited to 50 °C for the board using STLM20 (STEVAL- ILL009V4) and to 72 °C for the board using OSRAM module with NTC resistor (STEVAL- ILL009V3).

  • Page 25: Sw Pwm Frequency Calculation

    AN2531 STEVAL-ILL009V1 reference board 8.5.3 SW PWM frequency calculation In order to have a correct PWM signal on each output, it is necessary to always send data after the same time. This means that the t value must be always same (as...

  • Page 26: Software

    STEVAL-ILL009V1 reference board AN2531 Software The software is written in C language with several modules, but the most important files for proper operation of the STEVAL-ILL009V1 reference board are the following: main.c blink.c pwm_ar_timer_12bit.c spi.c adc_8bit.c Note: The final code has slightly less than 1.4 KBytes and it will fit the ST7FLITE09 memory.

  • Page 27: Figure 16. Blink Function Flowchart - First Part

    AN2531 STEVAL-ILL009V1 reference board The next block checks the temperature every 2.55 seconds. This time is considered fast enough because, due to its inertia, there is no need to check the temperature any faster. If its value is higher than the limit, the PWM duty cycle is increased (0% duty cycle is full bright and 100% is no light) by one step.

  • Page 28: Figure 17. Blink Function Flowchart - Second Part

    STEVAL-ILL009V1 reference board AN2531 number coming from ADC (potentiometer P1) has range from 0 to 252. This range is divided to six segments where always just one color is changed and two are constant (ON or OFF). Blue color is set if the potentiometer is in the left side (0 from ADC), because B = ON (blue), R = OFF (red) and G = OFF (green).

  • Page 29: Figure 18. Manual Color Modulation

    AN2531 STEVAL-ILL009V1 reference board Figure 18. Manual color modulation The last mode implemented is MODE 6, which is the simplest one - all the LEDs are turned ON, which produce the pure white color. Figure 19 describes this last part.

  • Page 30: Steval-Ill009V5 Reference Board

    20), efficiency improved and board size reduced. The STEVAL- ILL009V5 has 120 mm x 47 mm instead of 151 mm x 47 mm for the STEVAL-ILL009V1. The input voltage for the STEVAL-ILL009V5 ranges from 7 V to 18 V. The new LED drivers allow faster communications and higher output voltage.

  • Page 31: Steval-Ill009V5 Schematic Diagram

    AN2531 STEVAL-ILL009V5 reference board The STEVAL-ILL009V5 has the following differences to compare with the STEVAL- ILL009V1: 3 A at 4V DC/DC converter using the ST1S10 for input voltage range (7 V - 18 V) New improved LED drivers STP04CM05 and STP08CP05 Input over voltage protection done by Transil (SMAJ15A-TR) Protection against input voltage reversion Board size reduced from 151 mm x 47 mm to 120 mm x 47 mm.

  • Page 32: Bill Of Material

    AVX:12063D475MAT2A D1, D2, D3, D4, D5, Red LED OSRAM red LED Mini TOPLED LS M670-H2K1-1 D6, D7 Green LED SMD LED 1206 SMAJ15A-TR ST - Transil SMAJ15A-TR STPS340U ST - diode STPS340U D11, D12, D13, D14, BAT46 ST - Schottky diode...

  • Page 33: Steval-Ill009V3 Load Board

    The STEVAL-ILL009V3 demonstration board is shown in Figure 22. This board should be connected through the 30-pin connector to the STEVAL-ILL009V1 control board to be able to show the light effect with the board. The OSTAR projection module (refer to Chapter point 1), used as light source, has a maximum forward current 700 mA.

  • Page 34: Bill Of Material

    STEVAL-ILL009V3 load board AN2531 Equation 14 – – 0.6V F_RED_MAX Equation 15 0.85Ω diss RED_LED 10.2 Bill of material Table 5. STEVAL-ILL009V3 bill of material Item Quantity Reference Part Note Ordering code OSRAM OSTAR OSTAR projection module LE ATB A2A Projection Module Cable with connector 10 lines cable...

  • Page 35: Figure 23. Steval-Ill009V3 Schematic Diagram

    AN2531 STEVAL-ILL009V3 load board Figure 23. STEVAL-ILL009V3 schematic diagram Ω Ω 1. 5 5 1. 5 U_r = Ud - Uf_red_max = 4 - 3.4 = 0.6 V R_diss = U/I = 06 / 0.7 = 0.85 => 0.75 Ω CONNEC TOR1 R2 = R3 = 1.5 Ω...

  • Page 36: Steval-Ill009V4 Load Board

    12, point 2) used with a maximum forward current of 350 mA. As described in Chapter 8, the STEVAL-ILL009V1 can drive eight Golden DRAGON LEDs. To demonstrate the driving capability of the STP04CM596, only four LEDs are used on the load board. In fact, this means that one STP04CM596 driver is not used.

  • Page 37: Schematic Description

    DRAGON Green LED OSRAM Golden LRW5SM HY-1 Q65110A4386 DRAGON Red LED OSRAM Golden LBW5SM FX-3 Q65110A4396 DRAGON Blue LED 100 nF / 50 V Ceramic SMD1206 10 Ω R4, R5, R6 Through-hole resistor STLM20 ST temperature sensor STLM20W87F Connector2 30-pin connector 37/40...

  • Page 38: Figure 25. Steval-Ill009V4 Schematic Diagram

    STEVAL-ILL009V4 load board AN2531 Figure 25. STEVAL-ILL009V4 schematic diagram 38/40...

  • Page 39: Reference And Related Materials

    STMicroelectronics, SMAJ, Transil, Datasheet; www.st.com STMicroelectronics, L4973D3.3, 3.5 A step down switching regulator, Datasheet; www.st.com STMicroelectronics, L78L05, Positive voltage regulators, Datasheet; www.st.com STMicroelectronics, AN938, Designing with L4973, 3.5 A high efficiency DC-DC converter; www.st.com STMicroelectronics, STLM20, Ultra - low Current 2.4 V precision analog temperature sensor, Datasheet;...
  • Page 40 No license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted under this document. If any part of this document refers to any third party products or services it shall not be deemed a license grant by ST for the use of such third party products or services, or any intellectual property contained therein or considered as a warranty covering the use in any manner whatsoever of such third party products or services or any intellectual property contained therein.

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