AN2531 Application note
Generating multicolor light using RGB LEDs
Introduction
The new high power and brightness RGB LEDs are coming 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 Figure 1 was developed in order to 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 Projection Module (refer to Chapter 11, point 1) has ordering code STEVALILL009V3 and the second one with the Golden Dragon LEDs (refer to Chapter 11, 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. Figure 1. STEVAL-ILL009V1 reference board
May 2007
Rev 1
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www.st.com
Contents
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Contents
1 2 3 4 5 6 Driving concept for RGB LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 How to drive many LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 How to set high current for LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Color control - software modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Power dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Over-voltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.1 6.2 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Type of solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
7 8
LED temperature protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 STEVAL-ILL009V1 reference board . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8.1 8.2 8.3 8.4 8.5 General description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Getting started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Schematic description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Bill of materials (BOM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Design calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
8.5.1 8.5.2 8.5.3 LED supply voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Temperature protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 SW PWM frequency calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
8.6
Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
9
STEVAL-ILL009V3 Load board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.1 9.2 Schematic description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
10
STEVAL-ILL009V4 Load board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
10.1 10.2 Schematic description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
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Reference and related materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
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List of tables
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List of tables
Table 1. Table 2. Table 3. Table 4. Table 5. Table 6. BOM - STEVAL-ILL009V1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Temperature limit setting using STLM20 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Temperature limit setting using NTC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 STEVAL-ILL009V3 bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 STEVAL-ILL009V4 bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
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List of figures
List of figures
Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. Figure 11. Figure 12. Figure 13. Figure 14. Figure 15. Figure 16. Figure 17. Figure 18. Figure 19. Figure 20. Figure 21. Figure 22. Figure 23. STEVAL-ILL009V1 reference board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Driving concept for RGB LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 LED driver connection - serial configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 LED driver connection - parallel configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Common drain configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Software brightness modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 RGB LED configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Over-voltage on STP04CM596. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Possible over voltage protections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Temperature protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Components position on the STEVAL-ILL009V1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 STEVAL-ILL009V1 schematics - LED drivers part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 STEVAL-ILL009V1 power sources schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Send data time diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Main program flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Blink function flowchart - first part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Blink function flowchart - second part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Manual color modulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Blink function flowchart - third part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 STEVAL-ILL009V3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 STEVAL-ILL009V3 schematic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 STEVAL-ILL009V4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 STEVAL-ILL009V4 schematic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
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Driving concept for RGB LEDs
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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. The STP04CM596 is a high-power LED driver with 4-bit shift register designed for power LED applications. In the output stage, four regulated current sources provide 80-500 mA constant current to drive high power LEDs. Figure 2 shows the driving concept for RGB LEDs using an STP04CM596 LED driver. The LED supply voltage is connected to anodes of RGB LED and LEDs cathodes are connected to the ground through constant current sources. The supply voltage value is very important due to the power dissipation on drivers (detail explanation is described in Chapter 5). The value of the constant current is set by only one external resistor for all the four driver channels. The control unit in this application is a microcontroller, which sends data through serial peripheral interface (SPI) to the shift registers inside STP04CM596. The data are shifted bit by bit to the next drivers in a cascade with falling edge of the clock frequency (the maximum communication frequency for this drivers is 25 MHz). When all data are transmitted to the drivers through SPI, the micro sets latch input terminal (LE) pin "log 1" to rewrite the data to the storage registers and to turn on or off the LEDs. More details on timings and features are available in Application Note AN2141 (refer to Chapter 11, point 3) and Datasheet of the STP04CM596 (refer to Chapter 11, point 4). Temperature protection is designed in order to protect LEDs and increase their lifetime. A sensor (STLM20) is assembled close to the RGB LEDs and informs the microcontroller about RGB LED temperature. If the temperature is above its limit, the microcontroller decreases LED brightness (LED power) through PWM signal. An easy and user friendly hardware interface (potentiometers and buttons) was designed to demonstrate features such as color set, brightness regulation, mode changes, etc.
Figure 2.
Driving concept for RGB LEDs
LED supply voltage
IC supply voltage STP04CM596
Temperature sensor Full color pixel
Constant current CONTROL PANEL Micro SPI
Control and logic part
MODE
COLOR
I - reg.
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How to drive many LEDs
2
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. If the request is to control each RGB LED independently, a serial configuration (drivers in cascade connection) must be used as shown in Figure 3. The data are sent through all LED drivers via the SPI and then latched to the outputs. The main advantage is that current in each channel can be regulated by software PWM modulation, which in fact means color control of each RGB LED. The disadvantage of this solution is lower PWM resolution for a higher number of RGB LEDs, because it needs time to send data to all drivers. More information about this principle is described in Chapter 4: Color control - software modulation. If the request is to build up a high power light with many LEDs of the same color, drivers can be connected in parallel as shown in Figure 4. Main advantages are a simpler solution and better PWM resolution, because only four bits are sent through the SPI and it takes a short time. Color is also regulated by software PWM signals as described in Chapter 4.
Note:
It is also possible to mix serial and parallel configurations in order to provide several different colors with high lighting power. For example, two different colors using 10 RGB LEDs can be implemented using two STP04CM596 connected in series and five such blocks connected in parallel. LED driver connection - serial configuration
Figure 3.
SPI Micro STP04CM596
Serial connection
SPI
STP04CM596
Control and logic part
Control and logic part
LED supply voltage
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How to drive many LEDs Figure 4. LED driver connection - parallel configuration
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SPI Micro STP04CM596 Parallel connection STP04CM596
Control and logic part
Control and logic part
LED supply voltage
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How to set high current for LEDs
3
How to set high current for LEDs
The STP04CM596 is focused on driving high brightness and power LEDs and its output constant current can be set between 80 and 500 mA. In case a LED with even higher current is used, there is still a solution to control such LED using the STP04CM596. Thanks to a common drain configuration, the outputs can be connected together as shown in Figure 5. This increases the performance and current capability of this driver. This configuration allows driving the whole range of 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). Figure 5. Common drain configuration
STP04CM596
Rext
I-REG
Vo Vf + Vc Vo
Vo
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Color control - software modulation
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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. For one complete dimming cycle, the microcontroller sends a certain number of "0"s and "1"s to each LED. First, the microcontroller sends four bits in "logical 1" (i.e. 1111b or Fh) to the driver in order to turn ON all the output channels. Then microcontroller sends the same data (1111) until an output should be turned OFF (depending on desired preset color). (Each bit of the 4-bit frame controlling its corresponding output.) In this example, it is output 3 with green LED (6% duty cycle required). From that moment, the microcontroller keeps sending 1101. In the next step the output 1 with red LED (8% duty cycle) should be turned OFF and so data frame changes to 0101. This frame is sent until output 2 with blue LED (28% duty cycle) should be turned OFF and when the frame 0001 is used. Finally, the output 4 with another LED (usually second green LED) is turned OFF with 98% duty cycle, which means than 0000 is being sent until maximum time for one cycle is reached. After that, the entire period for all outputs can start again.
Figure 6.
Software brightness modulation
T SW_PWM 1111 1101 0101 0001 DATA T SEND_DATA LEVELS t 0000 1111 or new data
Output 1
8 % Duty Cycle t
Output 2
28 Duty Cycle t
Output 3
6 % Duty Cycle t
Output 4
98 % Duty Cycle
AI12678
The resolution of the LED dimming defines how many steps are possible to change the duty cycle from 0% to 100% (e.g. 6-bit means 64 steps; 7-bit means 128 steps and so on). It is obvious that it is preferred to design the control signal with a resolution as high as possible, but several limitations should be taken into account. Limitations concern mainly the speed of the serial communication interface inside the microcontroller (SPI) and the general calculation power of the microcontroller. First, the general LED frequency should be
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Color control - software modulation selected. This value is recommended to be above 100 Hz in order to avoid flickering as at 100 Hz and above it is not detected by the human eye and is considered as a stable light. Using Equation 1 and Equation 2, the resolution can be obtained as shown in Equation 3. Equation 1
t SW_PWM =
Equation 2
1 fSW_PWM
t SEND_DATA =
Equation 3
t SW_PWM LEVELS
1 × t SEND_DATA
LEVELS =
fSW_PWM
In order to have a good resolution, the time for sending data (tSEND_DATA) must be as short as possible. In an ideal case, this time takes into account the number of sent bits and the speed of the SPI clock (one bit is sent during one SPI period). As described in Figure 6, the number of sent bits corresponds to the number of driven LEDs, therefore in Equation 4, the number of driven LEDs is the same as number of bits sent (BITS = LEDS). Equation 4
t SEND_DATA =
BITS = t SPI_CLK × BITS fSPI_CLK
The maximum number of used LEDs is (assumption BITS = LEDS): Equation 5
LEDS =
Note:
1 fSW_PWM × t SPI_CLK × LEVELS
The above calculation is only valid only when the data are sent to the driver through the SPI without any delay. This means the data (BYTES) are sent thought the SPI and at the end of this communication the next data (BYTES) are immediately sent, etc. In case the data are sent through the SPI and then microcontroller executes some other instructions (checking temperature, checking ADC in order to set next PWM signal, etc.), the period (tSEND_DATA) for sending data is longer and it decreases the real maximum resolution.
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Power dissipation
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5
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
Pdmax =
Tjmax Ta R thja
Pd max . . ... maximum power dissipation [W] Ta . . .. . ..... ambient temperature [C] Tj max . . ..... maximum junction temperature [C] Rthja . . .. . . junction to ambient thermal resistance [C/W]. A high power RGB LED is in fact driven in linear mode with STP LED driver family. The current flowing through each channel of the LED driver is constant and so power dissipation depends on the voltage on each channel, which is the difference between the supply voltage (DC bus) and the forward voltage drop on the LEDs. Therefore it is recommended to keep the supply voltage as low as possible, but always above the maximum LED forward voltage. Figure 7 shows the RGB LED connection to the driver. Total power dissipation in this case is calculated using the following equation: Equation 7
Ptot = I * (VC Vf_red ) + I * (VC Vf_blue ) + 2 * I(VC Vf_green
Ptot. . .. . .. . ...power dissipation on chip [W] I. . .. . .. . .. . ..constant LED current set by external resistor [A] Vc. . .. . .. . ....LED supply voltage [V] Vf_red. . .. . ....red LED forward voltage [V] Vf_blue. . .. . ..blue LED forward voltage [V] Vf_green. . .. . .green LED forward voltage [V].
)
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Power dissipation
Figure 7.
RGB LED configuration
STP04CM596
Rext
I-REG
Vf_red Vo Vf_blue Vo Vf_green Vo Vf_green Vo
Vc
AI12679
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. There is quite simple way to decrease this power dissipation by using a serial resistor with the red LED. Calculation example is shown in Section 9.1 and 10.1.
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Over-voltage protection
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6.1
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. Generally, higher current and higher parasitic inductance (long cable) means higher voltage peaks. Therefore over voltage protection is very important for high brightness LEDs in case of long connections between the driver and LEDs.
Figure 8.
Over-voltage on STP04CM596
4 V at 3 A Temperature sensor STP04CM596 Maximum output voltage 16 V SPI
Control and logic part
Full color pixel Lp Lp Lp
Lp
Over-voltage
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Over-voltage protection
6.2
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 11, point 5) can be used. The second solution proposes to use a standard diode or Shottky diode as a freewheeling diode. Diodes are connected between the LED supply voltage (DC bus) and driver's channel and so limit the voltage on the channels. The third solution is the most cost effective and uses only a single zener diode which protects all channels. It can be used only if the connection between the LED driver and LED cathodes is a quite short and if the connection between LED supply voltage and anodes is long. This protection limits over voltage peaks on LED anodes.
Figure 9.
Possible over voltage protections
4 V at 3 A STP04CM596 Maximum output voltage 16 V SPI
Control and logic part
Lp Temperature sensor Full color pixel
Lp 3 D 1 Transil 2 Zener diode
Lp
Lp
Lp 4 Zener diode
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LED temperature protection
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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. Two different temperature protections are used in this design as shown in Figure 10 - the STLM20 temperature sensor and NTC (negative temperature coefficient) resistor. The STEVAL-ILL009V3 uses an NTC resistor directly assembled on the aluminum LED board (OSTAR projection module). The STEVAL-ILL009V4 has assembled the STLM20 temperature sensor in the middle of LEDs on the PCB. The microcontroller checks the voltage from the sensors and sets the correct output PWM signal on the OE pin of the LED drivers. The microcontroller can increase the duty cycle of the PWM signal (0% duty cycle is max bright and 100% duty cycle is no bright) or can turn OFF the RGB LED if over temperature occurs. Software implementation is up to designers. Temperature protection calculation using the STLM20 or NTC is presented in Chapter 8.5.2.
Figure 10. Temperature protection
STEVAL - ILL009V4
STEVAL - ILL009V3 Vc ADC R
STLM20
Micro NTC
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STEVAL-ILL009V1 reference board
8
STEVAL-ILL009V1 reference board
STEVAL-ILL009V1 reference board shown in Figure 1 was designed to demonstrate how high power and high brightness RGB LEDs can be driven and to confirm the principles described in the paragraphs above. This board has the following main features:
Different LEDs as a load can be used (additional boards connected through 30 pin connector) 8 LEDs with 350 mA can be driven (e.g. GOLDEN DRAGON module - STEVALILL009V4) 4 LEDs with 700 mA can be driven (e.g. OSTAR module - STEVAL-ILL009V3) LED over temperature protection using STLM20 or NTC resistor LED temperature limit set by software 3 A at 4 V DC/DC converter using L4973D3.3 for user friendly input (8 - 30 V) Color regulation (manual / auto) Brightness PWM regulation with 64 levels using OE pin (dimming all LEDs) Red, Green, Blue individual tuning White color preset mode LED frequency = 100 Hz 64 Levels of brightness for each LED with software color control 262144 color variations (64 x 64 x 64) SW start up implemented (200 ms) Over voltage protection implemented using clamp schottky diodes (BAT46) 6 different light MODES available Input over voltage protection done by transil (SMAJ33A) Over temperature signalization ICC connector for SW evaluation and change.
8.1
General description
Figure 11 shows components position on the STEVAL-ILL009V1. On the left side there is DC/DC converter with L4973D3.3 (ref. toChapter 11, point 6) with power capability 3 A at 4 V. The input voltage range is from 8 to 30 V and it is connected through input connector. The L78L05 (ref. to Chapter 11, point 7) provides 5 V supply voltage for the microcontroller and LED drivers (signal diode D8 is used to show connected power). Potentiometers P1 and P2 are used to set brightness for all LEDs or tuning each of them separately. High power RGB LEDs are driven by STP04CM596 and STP08CL596 is used to control signal LEDs (D1-D7) which are implemented to show which of the several lighting modes is currently set. 30 pins load connector provides better flexibility, because different types of LEDs can be connected to the same board. As an example two load boards with LEDs were designed STEVAL-ILL009V3 and STEVAL-ILL009V4.
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STEVAL-ILL009V1 reference board Figure 11. Components position on the STEVAL-ILL009V1
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8.2
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. 1. 2. Connect LED board to the STEVAL-ILL009V1 reference board using the 30-pin load connector2. STEVAL-ILL009V3 or STEVAL-ILL009V4 is LED boards. Connect the supply voltage between 8 to 30 V on the board using J1 connector. The power capability of the adapter must be higher then 14 W in order to have enough energy for the application.
Note:
The maximum channel current is set to 350 mA and so the LEDs and driver power consumption is PLEDout = 4V x 0.35 mA x 8 = 11.2 W. The efficiency of the DC/DC converter is approximately 80 % (PLEDin = 13.44 W). Considering the microcontroller and LED drivers themselves must be also supplied (consumption is less than 0.5 W) the total consumption is ~14 W and therefore the power capability of the adapter must be higher then 14 W in order to have enough energy for the application. 3. If the application is supplied, the green LED (D8) is lighted ON. It shows that there is a supply voltage for the micro and the drivers. Also LED D5 is turned ON at the start-up as the Automatic Color Control mode is set. Color automatically changes from blue to green, green to red and red to blue. During this mode, the brightness of all LEDs can be changed by potentiometer P2, but the function of the potentiometer P1 is disabled in this mode. Press the button (S2) to change the mode. The next mode is White Color Control mode. LED D7 is turned ON. The brightness of all LEDs can be changed by potentiometer P2 and the function of the potentiometer P1 is disabled in this mode. Press the button (S2) to set the next mode. It is Red Color Control mode. In this mode the brightness for the Red LED can be changed by potentiometer P1. There are 64 levels of brightness implemented. LED D1 is turned ON and the potentiometer P2 has the same function as in point 4 - changing the brightness of all LEDs. Press the button (S2) to set brightness for the Green LED. In this mode the brightness for the Green LED can be changed by potentiometer P1. LED D2 is turned ON. The potentiometer P2 has again the same function - changing the brightness of all LEDs.
4.
5.
6.
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AN2531 Note:
STEVAL-ILL009V1 reference board The brightness level of the RED light is set by previous mode and stored in the memory and so the effect of the GREEN color is added to the RED one. 7. Press the button (S2) to set brightness for the Blue LED. In this mode the brightness for the Blue LED can be changed by potentiometer P1. LED D3 is turned ON. The potentiometer P2 has the same function - changing the brightness of all LEDs.
Note:
The brightness levels of the RED and GREEN lights were set by previous modes and stored in the memory and so the BLUE color is added to the RED and GREEN one. 8. The next mode (press button S2) is a Manual Color Control mode. It means the color can be set as requested (going through predefined R-G-B curve) by the potentiometer P1. LED D4 is turned ON. The potentiometer P2 has the same function - changing the brightness of all LEDs. During all modes described above, LED temperature control is implemented. If over temperature occurs, the brightness of all LEDs is decreased by PWM signal on the general OE/ pin (64 levels). The temperature is checked every 2.55 s and if it is still above the limit, the duty cycle of PWM is further increased (OE/ pin has a "not output enable" function, i.e. higher the duty cycle lower the brightness and vice versa). The maximum temperature on the LED board is set to 50 C for the GOLDEN Dragon LEDs and 72 C for the OSTAR Projection module. Note that the higher temperature limit can be very easily set by software.
9.
10. How to demonstrate over temperature protection? Set full brightness by potentiometer P2 in White Color Control mode and wait approximately 3 minutes with STEVAL-ILL009V3 (board with heatsink) or 1½ minutes with STEVAL-ILL009V4 (board without heatsink). Temperature on LEDs is increased and if the over temperature is detected, LED D6 is turned ON and the PWM duty cycle is increased and the brightness decreased overcoming the potentiometer settings. The temperature of LED board then should go down and if no over temperature is detected after the period of time, the duty cycle is decreased again and normal operation is resumed.
8.3
Schematic description
The STEVAL-ILL009V1 reference board schematic diagram is shown in Figure 12 and Figure 13. It is divided into two figures for easier understanding. Figure 12 shows the components needed for LED driving. Resistors R2 and R3 set a maximum constant current 350 mA for each output channel of the STP04CM596. Thanks to this configuration, eight high brightness LEDs with the forward current 350 mA or 4 LEDs with the forward current 700 mA (two outputs are in parallel) can be driven. The STP08CL596 drives signal LED diodes with the constant current set to approximately 8 mA. The signal coming from the NTC resistor or STLM20 temperature sensor assembled in additional board (load boards) is filtered by a low-pass filter using capacitor C7 and resistor R6. Figure 13 shows the power sources for the application. A 12W DC-DC SMPS converter is built on L4973D3.3 and design calculations are described in the datasheet (ref. to Chapter 11, point 6) or in the AN938 (ref. to Chapter 11, point 8). The L78L05 is a linear voltage regulator with output voltage set to 5 V used for microcontroller and drivers supply.
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10 8 6 4 2
9 7 5 3 1
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C2 100 nF VCC IO3 VCC IO4 C3 100 nF C4 100 nF VCC IO1 IO 2 R1 R3 220 3 K
1 2 3 4 5 6 7 8 Vss PA0 VD D PA1 RESET PA2 AIN0 NC SCK NC AIN2ICCDATA MOSI ICCCLK CLKIN PA7 GND GND SDI CLK /LE OUT0 OUT1 NC VDD R_ext SDO /OE NC OUT3 OUT2 NC 16 15 14 13 12 11 10 9 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8
S1
VCC
STEVAL-ILL009V1 reference board
Switch
C1 10 nF C5 100 nF
VCC R2 220 STP04CM596 Vd
P1 10 K ST7F LITE09 STP04CM596
Brightness
1 2 3 4 5 6 7 8 GND GND SDI CLK /L E OUT0 OUT1 NC VDD R_ext SDO /OE NC OUT3 OUT2 NC 16 15 14 13 12 11 10 9
1 2 3 4 5 6 7 8
VD D GND SDI R-EXT CLK SDO /L E /OE OUT0 OUT7 OUT1 OUT6 OUT2 OUT5 OUT3 OUT4
16 15 14 13 12 11 10 9
VCC
STP08CL596
Color
P2 10 K VCC R5 10 K S2 IC C SWITCH CO NN ECTOR1 C6 10 nF D1 1 B AT 46 D1 2 B AT 46 D1 3 B AT 46 D1 4 B AT 46 D1 5 B AT 46 D1 6 B AT 46 D1 7 B AT 46 VCC R6 470 D1 8 B AT 46 VCC
R4
PROTECTION
4. 7 K
LED0 LED1 LED2 LED3 LED4 LED5 LED6 INFORMATION SIGNALS LED0 - RED LED CONTROL LED1 - GREEN LED CONTROL
Figure 12. STEVAL-ILL009V1 schematics - LED drivers part
C7 100 nF
1 2 3 4 5 6 7 8 9 10 1112 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 R1 G1a G1b B1 R2 G2a G2b B2 NC GND Vo VCC NC Vd Vd R1 G1a G1b B1 R2 G2a G2b B2 NC GND NC NC NC Vd Vd
LED2 - BLUE LED CONTROL LED3 - MANUAL COLOR CONTROL LED4 - AUTOMATIC COLOR CONTROL CO N CO NN ECTOR2 LED5 - OVER TEMPERATURE LED6 - WHITE COLOR
AI12671
AN2531
AN2531
L78L05A CD
VOUT
VC C 1 R7 C8 100 nF C10 33 F / 35 V D8 Green LED 390
IO5 8V
IN GND GND GND GND INHIB
C9 100 nF
23
6
7
5
INPUT VOLTAGE FROM 8 UP TO 30 V
R8 20 k
89 20 SYNC VF B BOOT SS 13 10 1 19 18 VCC VCC OSC
IO6 L4973D 3.3 C11 C21 100 nF 100 nF COILCRAFT
DMT2-149-3.8L
Vd
J1 CON3
1 2 3
D9 SMAJ33A-TR + R10 9.1 k C20 22 nF C13 470 F / 35 V C16 2,7 nF C17 100 nF C18 C19 100 nF 220 pF
C12 100 nF
12 11
OUT 2 V3.3 GND GND GND GND OUT 3 CO MP INH GND GND GND GND 4 5 6 7 14151617
L1 150 F C14 4700 F / 10 V + C15 100 nF R9 1.3 k
Figure 13. STEVAL-ILL009V1 power sources schematic
D10 STPS5L60
R11 6. 2 k
STEVAL-ILL009V1 reference board
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STEVAL-ILL009V1 reference board
AN2531
8.4
Table 1.
Item Qty 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 1 1 2 13 1 1 1 1 1 1 7 1 1 1 8 1 2 1 1 1 1 1 2 1 2 1 1 1 1 1 1 1 1 2
Bill of materials (BOM)
BOM - STEVAL-ILL009V1
Reference CONNECTOR1 CONNECTOR2 C1, C6 C2, C3, C4, C5, C7, C8, C9, C11, C12, C15, C17, C18, C21 C10 C13 C14 C16 C19 C20 D1, D2, D3, D4, D5, D6, D7 D8 D9 D10 D11, D12, D13, D14, D15, D16, D17, D18 IO1 IO2, IO3 IO4 IO5 IO6 J1 L1 P1, P2 R1 R2, R3 R4 R5 R6 R7 R8 R9 R10 R11 S1, S2 Part ICC CON 10 nF 100 nF 33 F / 35 V 470 F / 35 V 4700 F / 10 V 2,7 nF 220 pF 22 nF Red LED Green LED SMAJ33A-TR STPS5L60 BAT46 ST7FLITE09 STP04CM596 STP08CL596 L78L05 L4973D3.3 CON3 150 H 10 k 3 k 220 4.7k 10 k 470 390 20 k 1.3 k 9.1 k 6.2 k SWITCH Note 10 PIN 30 PIN Ceramic SMD1206 Ceramic SMD1206 Electrolytic Electrolytic Electrolytic Ceramic SMD1206 Ceramic SMD1206 Ceramic SMD1206 SMD LED 1206 SMD LED 1206 ST - Transil ST - Diode ST - Schottky diode ST - Microcontroller ST - LED driver ST - LED driver ST - Voltage regulator ST - DC/DC converter Input connector COILCRAFT Inductor Pot. with axis SMD resistors 1206 SMD resistors 1206 SMD resistors 1206 SMD resistors 1206 SMD resistors 1206 SMD resistors 1206 SMD resistors 1206 SMD resistors 1206 SMD resistors 1206 SMD resistors 1206 Switch DMT2-149-3.8L SMAJ33A-TR STPS5L60 BAT46JFILM ST7FLITE09Y0M6 STP04C596XTTR STP08CL596TTR L78L05ACD L4973D3.3 Ordering code
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STEVAL-ILL009V1 reference board
8.5
8.5.1
Design calculation
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). Therefore L4973D3.3 DC-DC converter with output power capability 12 W - 4 V at 3 A was designed. The output voltage is calculated in Equation 8: Equation 8
VF = Vd
Where: VF. . ... Converter feedback input - > 3.3 V Vd . . .. LED supply voltage --> 4 V
R11 R11 + R 9
From Equation 9 below resulting R9 = 1300 (R11 is chosen 6.2 k) Equation 9
R9 = R11
8.5.2 Temperature protection
Vd VF 4 3.3 = 6.2 × = 1.3K VF 3.3
Using STLM20 temperature sensor
The STLM20 is a precise analog temperature sensor for low current applications. It operates over a 55 to 130 C (Grade 7) or 40 to 85 C (Grade 9) temperature range. The power supply operating range is 2.4 to 5.5 V. The accuracy of the STLM20 is 1.5 C, at an ambient temperature of 25 C. More information about the STLM20 is described in the datasheet (refer to Chapter 11, point 9). A simple linear transfer function, with good accuracy near 25 C is expressed as: Equation 10
Vo = 11.79mV/C × T + 1.8528V = 11.79 × 10 3 × 50 + 1.8528 = 1.263V
If the sensor temperature is 50 C, the output voltage is 1.263 V (resulting from Equation 10). This analog voltage is then sensed by the 8-bit ADC with an input voltage range 0 to 5 V inside the microcontroller. This number is used by software to limit the temperature. The software also includes the table with pre-calculated integer numbers for temperatures of 60, 70 and 80 C and so it is very easy to change temperature limits (see Table 2). Note: Temperature limit set to 50 C was chosen in order to demonstrate temperature limitation feature (it takes a long time to heat LEDs assembled on heatsink to high temperature). In final application higher temperature limit can be set according the LEDs used and their maximum operating temperature.
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STEVAL-ILL009V1 reference board Table 2. Temperature limit setting using STLM20
Sensor voltage [V] 1.263 1.145 1.027 0.909
AN2531
Temperature [C] 50 60 70 80
ADC integer number 65 59 53 47
Using NTC resistor on the OSTAR module
Figure 10 shows a voltage divider using resistor R and NTC resistor to obtain a voltage in function of temperature. Resistor was chosen R = 4700 and the calculated sensor voltage and ADC integer number according used NTC resistance for 50, 60, 70 and 80 C using following equation: Equation 11
Vsensor = VCC ×
Note: VCC = 5 V.
NTC NTC + R
The software also includes a look-up table with pre-calculated integer numbers for 50, 60, 70 and 80 C and so it is very easy to change the temperature limit (see Table 3). 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 (STEVALILL009V4) and to 72 C for the board using OSRAM module with NTC resistor (STEVALILL009V3). Table 3. Temperature limit setting using NTC
NTC resistance [k] 3.5 2.5 1.7 1.3 Sensor voltage [V] 2.13 1.73 1.32 1.08 ADC integer number 109 89 68 55
Temperature [C] 50 60 70 80
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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 tSEND_DATA value must be always same (as explained in Figure 6). The ST7FLITE09 microcontroller has a 12-bit auto-reload timer used to generate a constant time base for data sending. It is set to 156 s and so after each 156 s period, the data are sent. Resolution is 6 bits and therefore 64 brightness levels are available. One period of the SW dimming signal is: Equation 12
t SW_PWM = LEVELS × t SEND_DATA = 64 × 156 × 10 6 = 9.984ms
Equation 13
fSW_PWM =
Note:
1 t SW_PWM
=
1 = 100.16 Hz 9.984 × 10 3
Some applications often require a PWM frequency higher than 100 Hz (even 100 Hz is observed as a still color without any flickering) and also a PWM resolution higher than 6-bit (64 LEVELS). Figure 14 shows the waveform of SPI clock frequency that explains why the 6-bit resolution of the PWM signal and frequency 100 Hz was designed. The time for sending data is 156 s, but the SPI communication takes only 4 s (8 bit times 0.5 s - SPI clock is 2 MHz) and the rest (152 s) is software execution due to many features as temperature protection, lighting modes, ADC reading, etc. As shown, there is still room to improve the SW PWM resolution by decreasing time for data sending. Software improvements that demonstrate higher resolutions are already under development even with existing hardware only done by code optimization. Figure 14. Send data time diagram
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STEVAL-ILL009V1 reference board
AN2531
8.6
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. Main programming flowchart is shown in Figure 15. The program starts in main.c and initializes the microcontroller functions such as RC oscillator calibration, ports initialization, PWM AR timer setting for time base generation and SPI initialization (SPI clock frequency). Afterwards, the interrupts are enabled and the program runs in a never-ending loop in function blink.c. Basically three interrupts can occur. First, an AR timer overflow interrupt, which generates a time base 156 s for the software dimming in order to have precise brightness regulation. When this interrupt occur, the program checks if all data have been already sent through SPI or not. If not the data are missed and the program waits for next interrupt (156 s), but it is only some kind of backup protection. The second interrupt is a SPI interrupt, which informs that data (single byte) have been already sent. The last interrupt is an external input interrupt, which detects that button was pressed. Figure 15. Main program flowchart
FLOWCHARTS for the RGB color control board MAIN AR_Timmer_OF interrupt after each 156 s
SPI interrupt
Microcontroller initialization
All DATA are sent Y Time base ON
N
All DATA are sent YES
Enable interrupts
Return
Main procedure BLINK
Return
AI12683
The heart of the software is a blink function running in a never-ending loop. In the start part (Figure 16), the program waits until a PWM interrupt occurs during synchronization then the Counter_SW value is incremented. Generally, Counter_SW represents the number of levels for the software PWM modulation and in this case it is 64 (6-bit resolution) (described in detail in Chapter 4). The Brightness value set by potentiometer P2 is converted by the ADC to a value between 0 and 64 in each SW PWM period (each 10 ms / 100 Hz) and this value sets the PWM brightness on the Output Enable (OE) pin.
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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. Therefore, the light is absolutely turned OFF after 163.2 seconds (64 levels times 2.55). If the temperature is lower then the limit, the PWM duty cycle starts decreasing down to maximum brightness (0%) and normal operation. Time3 = 200 ms is used as a stabilization time for the DC-DC converter and linear regulator. The output capacitors C10 and C14 (Figure 13) should be charged first to avoid resetting the microcontroller (low voltage detector) and the flickering application due to the high load. At the end, the high power RGB LEDs are turned ON after 200 ms. This time delay occurs only once, when the application starts.
Figure 16. Blink function flowchart - first part
Start BLINK 1
Time1 = 2.55 s N Time base 156 s ? Y Counter_SW ++
255 x 64 x156 s
Y Time2 = 0
N Temperature Limit > measured value N Increase bright about 1 step Read brightness from potentiometer P2 (digital value from ADC) Time1 = 0 Y
Negative temperature coeficient
Decrease bright about 1 step
Y Time1 = 10 ms
64 x 156 s
N
Time3 = 200 ms
20 x 64 x156 s
Time3 = 0 Startup = OFF
1 2
AI12684
Figure 17 shows the second part of the blink function - the brightness setting (based on value read on P2 in first part) and mode selection (mode is selected by pressing button S2). MODE 1, MODE 2 and MODE 3 sets the brightness for the red, green and blue LEDs where the brightness level (0 to 64) is obtained from the potentiometer P1 after each SW PWM period (10 ms). R, G & B elements could be set in single step with MODE 4 and MODE 5. This means the color is moving on a predefined curve as indicated in Figure 18. The difference between MODE 4 and MODE 5 is that MODE 4 is controlled by potentiometer P1 and MODE 5 is working automatically (simulating the P1 input). Figure 18 shows how it works. The integer
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STEVAL-ILL009V1 reference board
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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). If the value from ADC is increased to 42, the PWM of green color is decreased. In case ADC has value 42 the green is fully turned ON together with blue and red is OFF. The ADC value from 43 to 84 increases blue color (light is going down) and if ADC has value 84 only green LED is ON. In this way it is possible to move light through all basic colors. MODE 5 represents automatic color changing. The principle of the automatic color change is similar to manual color control, because the color level is not adjusted by potentiometer P1 (0-252), but automatically using the 156 s time base generated by the auto-reload timer. Note: In order to demonstrate the best lighting effects, the application automatically starts in MODE 5 - automatic color changing mode.
Figure 17. Blink function flowchart - second part
2 Set bright PWM on OE pin 3
MODE 3
Y Set BLUE bright
Mode changed
Y Set starting conditions
N
Set DATA_blink1 Set DATA_blink2
N
MODE 4 Y MODE 1 Set RED bright N Set DATA_blink1 Set DATA_blink2 MODE 5 Y MODE 2 Set GREEN bright N Set DATA_blink1 Set DATA_blink2 3 4 N N
Y Set manual color Set DATA_blink1 Set DATA_blink2
Y Startup = ON Set auto color Set DATA_blink1 Set DATA_blink2 Overtemperature
AI12685
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AN2531 Figure 18. Manual color modulation
STEVAL-ILL009V1 reference board
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. Figure 19. Blink function flowchart - third part
4 Y MODE 6 Set WHITE color N Set DATA_blink1 Set DATA_blink2 Default
Y Counter_SW = 64 Counter_SW = 0 N
Write to the SPI Register SPIDR = DATA_blink1 SPIDR = DATA_blink2
Return Blink procedure starts again
AI12686
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STEVAL-ILL009V3 Load board
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9
STEVAL-ILL009V3 Load board
The STEVAL-ILL009V3 demo board is shown in Figure 20. 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 11, point 1), used as light source, has a maximum forward current 700 mA. The NTC resistor is directly assembled on the OSTAR module. As the power of the module is above 10 W the heatsink had to be designed in order to keep the temperature in range. The biggest advantage of the OSTAR module is that red, green and blue LEDs are in the same package, very closely assembled and therefore color effect is better than with three separate LEDs. Figure 20. STEVAL-ILL009V3
9.1
Schematic description
The schematic of the STEVAL-ILL009V3 is shown in Figure 21. As described, the constant current flowing through each channel is set to 350 mA, but because 700 mA is needed to drive the OSTAR module, two outputs are connected in parallel (Figure 21). Resistor R4 represents together with the NTC resistor the voltage divider for the temperature sensing (described in detail in Chapter 8.5.2). The software has a preset temperature limitation 50 C for Golden Dragon LEDs using STLM20 temperature sensor, which means a voltage of 1.263 V on the ADC. The NTC has a resistance of 1588 at72 C and the voltage coming from resistor divider to the ADC is exactly 1.263 V. So, the default temperature limit for the OSTAR module is 72 C, but it can be very easy changed by software. The HB LEDs are supplied from the DC/DC converter 4 V at 3 A. The maximum green and blue LEDs forward voltage is 4 V, but the red forward voltage is 3.4 V. If 3.4 V is around red LED, the rest of the supply voltage (4 V) must be on the driver (0.6 V) causing a power loss and therefore the design includes the connection of resistors R1, R2 and R3 to decrease power dissipation on LED drivers and move these losses to the resistors.
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AN2531 Equation 14
STEVAL-ILL009V3 Load board
VR = Vd VF_RED_MAX = 4 3.4 = 0.6V
Equation 15
R diss =
VR IRED_LED
=
0.6 = 0.85 0.7
9.2
Bill of materials
Table 4. STEVAL-ILL009V3 bill of materials
Reference OSTAR projection module Cable with connector Heatsink Connector1 Female Connector1 Connector2 R1 R2, R3 R4 0 1.5 4.7 k Through-hole 0.6 W Through-hole 0.6 W Part Note OSRAM OSTAR Projection Module 10 lines cable SEMIC Trade 10 pins 10 pins 30-pin connector Ordering code LE ATB A2A SHR-10V-S-B -> JST 8150/50/N Item Quantity 1 2 3 4 5 6 7 8 9 1 1 1 1 1 1 1 2 1
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STEVAL-ILL009V3 Load board Figure 21. STEVAL-ILL009V3 schematic diagram
AN2531
R2
R3 1. 5
1. 5 10 8 6 4 2 ICC 9 7531 CONNEC TO R1 R1 0
U_r = Ud - Uf_red_max = 4 - 3.4 = 0.6 V R_diss = U/I = 06 / 0.7 = 0.85 => 0.75 R2 = R3 = 1.5 R2 || R3 = 0.75
R4 47 k 5V
4700
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 2526 27 28 29 30 R1 G1a G1b B1 R2 G2a G2b B2 NC GND NC NC NC Vd Vd R1 G1a G1b B1 R2 G2a G2b B2 NC GND Vo Vcc NC Vd Vd
NTC
1.263 V for 72 C
ICC
CONNECT OR 2
R_ntc (72 C) = 1588 AI12673
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STEVAL-ILL009V4 Load board
10
STEVAL-ILL009V4 Load board
The STEVAL-ILL009V4 demo board is shown in Figure 22. This board is an option to the STEVAL-ILL009V3. As a light source, there are four Golden Dragon LEDs (refer to Chapter 11, 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. The STLM20 temperature sensor is assembled in the middle of the LEDs to protect against overheating (as described in Section 8.5). Figure 22. STEVAL-ILL009V4
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STEVAL-ILL009V4 Load board
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10.1
Schematic description
The schematic of the STEVAL-ILL009V4 is shown in Figure 23. The temperature limitation of the Golden Dragon LEDs is set to 50 C on this board. Similar to the STEVAL-ILL009V3, resistors R4, R5 and R6 are used to decrease the power dissipation on LED driver. The resistor value is calculated using the following equation: Equation 16
VR = Vd VF_RED_MAX = 4 2.6 = 1.4V
Equation 17
R=
VR IRED_LED
=
1.4 = 4 0.35
10.2
Bill of materials
Table 5.
Item 1 2 3 4 5 6 7
STEVAL-ILL009V4 bill of materials
Quantity 2 1 1 1 3 1 1 Reference G1a, G1b R1 B1 C7 R4, R5, R6 IO7 Connector2 Part LTW5SM HZ-3 LRW5SM HY-1 LBW5SM FX-3 100 nF / 50 V 10 STLM20 Note OSRAM Golden Dragon Green LED OSRAM Golden Dragon Red LED OSRAM Golden Dragon Blue LED Ceramic SMD1206 Through-hole resistor ST Temperature sensor 30-pin connector STLM20W87F Ordering code Q65110A5876 Q65110A4386 Q65110A4396
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R4 10 U_r = U_d - U_f_red = 4 - 2.6 = 1.4 V R = U_r / I = 1,4 / 0.35 = 4 => 3.3 used (R4||R5||R6)
R5 10
R6 10
R1 VCC Temperature sensor IO5 4 C7 5 100 nF V+ Vo GND GND NC STLM 20 3 2 1
Figure 23. STEVAL-ILL009V4 schematic diagram
G1a
G1b
B1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
R1 R1 Vd Vd B1 R2 G2 a G2 b B2 NC GND NC NC NC G1 a G1 b G1a G1 b B1 R2 B2 NC GND Vo VCC NC Vd Vd G2 a G2 b
STEVAL-ILL009V4 Load board
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ICC
CONNECTOR2
AI12674
Reference and related materials
A N2531
11
Reference and related materials
1. 2. 3. 4. 5. 6. 7. 8. 9. OSRAM Opto Semiconductors, LE ATB A2A, Datasheet of OSTAR Projection Module http://www.osram-os.com OSRAM Opto Semiconductors, Datasheet of GOLDEN Dragon LEDs http://www.osram-os.com STMicroelectronics, AN2141, LEDs Array Reference Board Design http://www.st.com STMicroelectronics, STP04CM596, 4-bit constant current for power-LED sink driver, data-sheet; http://www.st.com STMicroelectronics, SMAJ, Transil, Datasheet; http://www.st.com STMicroelectronics, L4973D3.3, 3.5 A step down switching regulator, Datasheet; http://www.st.com STMicroelectronics, L78L05, Positive voltage regulators, Datasheet; http://www.st.com STMicroelectronics, AN938, Designing with L4973, 3.5 A high efficiency DC-DC converter http://www.st.com STMicroelectronics, STLM20, Ultra - low Current 2.4 V precision analog temperature sensor, Datasheet; http://www.st.com.
12
Revision history
Table 6.
Date 3-May-2007
Document revision history
Revision 1 Initial release. Changes
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