ST STEVAL-ILL009V1 Application Note

AN2531

Applica t ion note

Generating multicolor light using RGB LEDs

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 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
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 STEVAL­ILL009V5 reference design is described in Chapter 9.

Figure 1. STEVAL-ILL009V1 reference board

®

Projection Module (refer to Chapter 12, point 1) has ordering code STEVAL-

®

LEDs (refer to Chapter 12,

September 2008 Rev 2 1/40

www.st.com

Contents AN2531

Contents

1 Driving concept for RGB LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2 How to drive many LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3 How to set high current for LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4 Color control - software modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

5 Power dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

6 Over voltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6.1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6.2 Type of solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

7 LED temperature protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

8 STEVAL-ILL009V1 reference board . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

8.1 General description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

8.2 Getting started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

8.3 Schematic description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

8.4 Bill of m at erial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

8.5 Design calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

8.5.1 LED supply voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

8.5. 2 Temperature p r o tection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

8.5.3 SW PWM frequen cy calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

8.6 Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

9 STEVAL-ILL009V5 reference board . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

9.1 STEVAL-ILL009V5 schematic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . 31

9.2 Bill of m at erial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

10 STEVAL-ILL009V3 load board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

10.1 Schematic description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

10.2 B ill of m at erial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

2/40

AN2531 Contents

11 STEVAL-ILL009V4 load board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

11.1 Schematic description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

11.2 B ill of m at erial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

12 Reference and related materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

13 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

3/40

List of tabl es AN2531

List of tables

Table 1. BOM - STEVAL-ILL009V1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Table 2. Temperature limit setting using STLM20 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Table 3. Temperature limit setting using NTC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Table 4. ST EVAL-I LL009V5 bil l of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Table 5. STEVAL-ILL009V 3 bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Table 6. STEVAL-ILL009V 4 bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Table 7. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

4/40

AN2531 List of figures

List of figures

Figure 1. STEVAL-ILL009V1 reference board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Figure 2. Driving concept for RGB LEDs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Figure 3. LED driver connection - serial configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure 4. LED driver connection - parallel configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Figure 5. Common drain configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 6. Software brightness modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 7. RGB LED configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 8. Over voltage on STP04CM596. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 9. Possible over voltage protections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 10. Temperature protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 11. Components position on the STEVAL-ILL009V1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 12. STEVAL-ILL009V1 schem atics - LED drivers part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 13. STEVAL-ILL009V1 power sources schemat ic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 14. Send data time diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Figure 15. Main program flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Figure 16. Blink function flowchart - first part. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Figure 17. Blink function flowchart - second part. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Figure 18. Manual color modulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Figure 19. Blink function flowchart - third part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Figure 20. STEVAL-ILL009V5 reference board. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Figure 21. STEVAL-ILL009V5 power sources schematic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Figure 22. STEVAL-ILL009V3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 23. STEVAL-ILL009V3 schematic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Figure 24. STEVAL-ILL009V4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Figure 25. STEVAL-ILL009V4 schematic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

5/40

Driving concept for RGB LEDs AN2531

1 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 L E D. In this application, the microcontrolle r
provides three software PWM signals (principle is described below in Chapter 4) for LE D
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 12, point 3)
and Datasheet of the STP04CM596 (refer to Chapter 12 , 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

IC supply

voltage

CONTROL PANEL

SPI

MODE

Micro

COLOR

STP04CM596

Control

and

logic

part

LED supply

Constant

current

I - reg.

voltage

Temperature sensor

Full color pixel

6/40

AM00285

AN2531 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 b uild up a high po wer l i ght wit h m any 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. F or exam ple, two diff erent colors using 10 RGB LEDs can be
implemented using two STP04CM596 connecte d in series and five such blocks connected
in parallel.

Figure 3. LED driver connection - serial configuration

SPI

Micro

STP04CM596

Control

and

logic

part

LED supply

voltage

Serial connection

SPI

STP04CM596

Control

and

logic

part

AM00286

7/40

How to drive many LEDs AN2531

Figure 4. LED driver connection - parallel configuration

SPI

Micro

LED supply

voltage

STP04CM596

Control

and

logic

part

Parallel connection

STP04CM596

Control

and
logic
part

AM00287

8/40

AN2531 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 c urrent 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

I-REG

R

ext

V

o

V

f

+ V

c

V

o

V

o

AM00288

9/40

Color control - software modulation AN2531

4 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 fo r a fourth LED. For one comple te dimming cycle, the microcontroller sends a certain
number of “0”s and “1”s to each LED. Fi rst, 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 b it 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 o ne cycl e is reac hed. After that, the entire period for a ll outputs can start
again.

Figure 6. Software brightness modulation

T

SW_PWM

1111 1111 or new data1101 0101 0001 0000

DATA

T SEND_DATA

Output 1

Output 2

Output 3

Output 4

LEVELS

t

8 % duty cycle

t

28 duty cycle

t

6 % duty cycle

t

98 % duty cycle

AM00289

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 sev eral 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
selected. This value is recommended to be above 100 Hz in order to avoid flickering as at

10/40

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 and Equation 2, the resolution can be obtained as shown in Equation 3.

Equation 1

t =

SW_PWM

Equation 2

t

SEND_DATA

Equation 3

LEVELS×=

In order to have a good resolution, the time for sending data (t
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

f

SPI_CLK

f

SW_PWM

t

SW_PWM

=

LEVELS

1

1

tf

SEND_DATASW_PWM

SPI_CLK

SEND_DATA

BITSt

×==

) must be as short

The maximum number of used LEDs is (assumption BITS = LEDS):

Equation 5

LEDS

Note: 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 (t
resolution.

SEND_DATA

) for sending data is longer and it decreases the real maximum

=

1

LEVELStf

SPI_CLKSW_PWM

××

11/40

Power dis si pat i on AN2531

(

)

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

T–T

P =

dmax

P

……. maximum power dissipation [W]

d max

……….…. ambient temp erature [°C]

T

a

……... maximum junction temperature [°C]

T

j max

………. junction to ambient thermal resistance [°C/W].

R

thja

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 abov e 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:

R

ajmax

thja

Equation 7

()( )

P

……….…….power dissipation on chip [W]

tot

I…………………constant LED current set by external resistor [A]

………………L E D suppl y voltage [V]

V

c

………….red LED forward voltage [V]

V

f_red

….…….blue LED forward voltage [V]

V

f_blue

V

……....green LED forward voltage [V].

f_green

V–VI*2V–V*IV–V*IP ++=

f_greenCf_blueCf_redCtot

12/40

AN2531 Power dissipati on

Figure 7. RGB LE D configurati on

STP04CM596

I-REG

R

ext

V

f_red

V

o

V

f_blue

V

o

V

f_green

V

o

V

f_green

V

o

V

c

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. 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 10.1 and 11.1.

13/40

Over voltage protection AN2531

6 Over voltage protection

6.1 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

Full color pixel

SPI

Control

and

logic

part

Over voltage

Lp

Lp

Lp

Lp

AM00291

14/40

AN2531 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 bet ween each chan nel 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.

The second solution proposes to use a standard diode or Schottky 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

STP04CM596

SPI

Control

and

logic

part

Maximum output

voltage 16 V

Transil

4 V at 3 A

3

21

Zener

diode

Lp

Temperature sensor

Full color pixel

Lp

D

Lp

Lp

Lp

4

Zener

diode

AM00292

15/40

LED temperature protection AN2531

7 LED temperature protection

The STEVAL-009V1 was designed for high power RGB LEDs with a nominal power even
higher then ten watts. As the life t ime 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

STLM20 Micro

R

NTC

AM00293

16/40

AN2531 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 startup 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. to Chapter 12, 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 12, point 7) provides 5 V supply voltage for the microcontroller
and LED drivers (signal diode D8 is used to show connected power). Po tentiometers 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.

17/40

STEVAL-ILL009V1 reference board AN2531

Figure 11. Components position on the STEVAL-ILL009V1

8.2 Getting started

Getting started chapter briefly describes how to use the STEVAL-I LL009V 1 as a step by
step guide in order to quickly start with the evaluation.

1. Connect LED board to the STEVAL-ILL009V1 reference board using the 30-pin load
connector2. STEVAL-ILL009V3 or STEVAL-ILL009V4 is LED boards.

2. Conn ec t 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

consumptio n i s P
is approximately 80 % (P

= 4V x 0.35 mA x 8 = 11.2 W. The efficiency of the DC/DC converter

LEDout

= 13.44 W). Considering the microcontroller and LED drivers

LEDin

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.

4. 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.

5. 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.

6. P ress 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.

18/40

AN2531 STEVAL-ILL009V1 reference board

Note: 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.

9. 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.

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). T emperature 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 F igure 12 and

Figure 13. It is divided into two figures for eas ier 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 12, point 6) or in the AN938 (ref. to Chapter 12, point 8). The L78L05 is a linear

voltage regulator with output voltage set to 5 V used for microcontroller and drivers supply.

19/40

STEVAL-ILL009V1 reference board AN2531

Figure 12. STEVAL-ILL009V1 schematics - LED drivers part

R1

CC

V

C4 100 nF

15

16

14

DD

V

SDO

R-EXT

GND1SDI2CLK3/LE4OUT05OUT16OUT27OUT3

IO4

13

/OE

3 KΩ

9

OUT712OUT611OUT510OUT4

8

STP08CL596

AM00294

CC

V

C3 100 nF

CC

V

C2 100 nF

IO3

IO2

IO1

15

16

DD

V

GND1GND2SDI3CLK

16

15

DD

V

GND1GND2SDI3CLK

16

SS

V

V

2

1

14

R_ext

14

R_ext

DD

R3

11

13

9

12

NC

/OE

SDO

OUT210OUT3

/LE5OUT06OUT17NC

8

4

R2

11

13

9

12

NC

/OE

SDO

OUT210OUT3

/LE5OUT06OUT17NC

8

4

9

10

11

13

NC12NC

PA214PA115PA0

ICCCLK

ICCDATA

RESET3AIN04SCK5AIN26MOSI7CLKIN

8

NC

NC

PA7

220

220

Vd

STP04CM596

596

STP04CM

LI

ST7FLITE09

LED0

LED1

LED2

PROTECTION

1 BAT46

D13 B AT46

D12 B AT46

D14 B AT46

D1

S2

R5 10 KΩ

CC

V

2
4
6
8

10

LED3

D15 B AT46

C6

10 nF

SWITCH

CC

I

LED4

CONNECTOR1

1
3
5

7
9

INFORMATION SIGNALS

LED5

LED6

CC

V

D18 B AT46

D16 B AT46

D17 B AT46

CC

V

LED0 - RED LED CONTROL

LED1 - GREEN LED CONTROL

LED2 - BLUE LED CONTROL

LED3 - MANUAL COLOR CONTROL

LED4 - AUTOMATIC COLOR CONTROL

LED5 - OVER TEMPERATURE

LED6 - WHITE COLOR

Vd

30

Vd

29

Vd

28

Vd

27

NC

26

NC

25

CC

V

24

NC

23

Vo

22

NC

21

GND

20
19

GND

NC

18

NC

17

B2

16

B2

15
14

G2b

CONNCON ECTOR2

13

G2b

12

G2a

11

G2a

R2

10

R2

9

B1

8

B1

7
6

G1b

5

G1b
a

4

G1a

3

G1

R1

2

R1

1

R6 470

CC

V

C5

100 nF

C1

10 nF

C1

CC

V

Brightness

P1

S1

Switch

R4

Color

CC

P2

V

10 KΩ

20/40

C7

100 nF

4.7 KΩ

10 KΩ

AN2531 STEVAL-ILL009V1 reference board

Figure 13. STEVAL-ILL009V1 power sources schematic

R11

9.1 kΩ

C17

D10

C20

C2

100 nF

6.2 kΩ

STPS5L60

22 nF

C19

220 pF

C18

100 nF

AM00295

V

CC

IO5 L78L05ACD

R9

1.3 kΩ

Vd

C15

100 nF

+

DMT2-149-3.8L

COILCRAFT

L1

R7

1

OUT

V

IN

V

8

D8

390 Ω

Green LED

/

0
C1

35 V

33 µF

C8

100 nF

B

5

INHI

7

GND

6

GND

GND

3

GND

2

C9

100 nF

IO6

R8

C21

C11

13

10

VFB

BOOT

L4973D3.3

SYNC

20

CC

V

9
8

CC

V

OSC

SS19V3.3

1

20 kΩ

100 nF

2

100 nF

OUT3OUT
GND
GND
GND
GND

18

GND
GND

GND

GND
INH

COMP

150 µF

17

16
15
14

7
6
5
4

11
12

4700 µF / 10 V

C14

R10

2,7 nF

C16

+

+

C12

100 nF

C13

D9

SMAJ33A-TR

470 µF /35 V

123

J1 CON3

FROM 8 UP TO 30 V

INPUT VOLTAGE

21/40

STEVAL-ILL009V1 reference board AN2531

8.4 Bill of material

Table 1. BOM - STEVAL-ILL009V1

Item Qty Reference Part Note Ordering code

1 1 CONNECTOR1 I

CC

10 PIN
2 1 CONNECTOR2 CON 30 PIN
3 2 C1, C6 10 nF Ceramic SMD1206

413

C2, C3, C4, C5, C7, C8, C9, C11, C12,
C15, C17, C18, C21

100 nF Ceramic SMD1206

5 1 C10 33 µF / 35 V Electrolytic
6 1 C13 470 µF / 35 V Electrolytic
7 1 C14 4700 µF / 10 V Electrolytic
8 1 C16 2,7 nF Ceramic SMD1206
9 1 C19 220 pF Ceramic SMD1206

10 1 C20 22 nF Ceramic SMD1206
11 7 D1, D2, D3, D4, D5, D6, D7 Red LED SMD LED 1206
12 1 D8 Green LED SMD LED 1206
13 1 D9 SMAJ33A-TR ST - Transil SMAJ33A-TR
14 1 D10 STPS5L60 ST - dio de STPS5L60
15 8 D11, D12, D13, D14, D15, D16, D17, D18 BAT46 ST - Schottky diode BAT46JFILM
16 1 IO1 ST7FLITE09 ST - microcontroller ST7FLITE09Y0M6
17 2 IO2, IO3 STP04CM596 ST - LED driver STP04C596XTTR
18 1 IO4 STP08CL596 ST - LED driver STP08CL596TTR
19 1 IO5 L78L05 ST - voltage regula tor L78L05ACD
20 1 IO6 L4973D3.3 ST - DC/DC converter L4973D3.3
21 1 J1 CON3 Input connector
22 1 L1 150 µH Coilcraft inductor DMT2-149-3.8L
23 2 P1, P2 10 kΩ Pot. with axis
24 1 R1 3 kΩ SMD resistors 1206
25 2 R2, R3 220 SMD resistors 1206
26 1 R4 4.7kΩ SMD resistors 1206
27 1 R5 10 kΩ SMD resistors 1206
28 1 R6 470 Ω SMD resistors 1206
29 1 R7 390 Ω SMD resistors 1206
30 1 R8 20 kΩ SMD resistors 1206
31 1 R9 1.3 kΩ SMD resistors 1206
32 1 R10 9.1 kΩ SMD resistors 1206
33 1 R11 6.2 kΩ SMD resistors 1206
34 2 S1, S2 Switch Switch

22/40

AN2531 STEVAL-ILL009V1 reference board

8.5 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).
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

R

dF

6.2

11

RR

3.3

911

3.3–4

=×==

1.3KΩ

VV+=

Where:
V

……. Converter feedback input - > 3.3 V

F

V

…… LED supply voltage --> 4 V

d

From Equation 9 bel ow resulting R9 = 1300 Ω (R11 is chosen 6.2 kΩ)

Equation 9

V–V

RR

119

V

Fd

F

8.5.2 Temperature protection

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 12, point 9).

A simple linear transfer function, with good accuracy near 25 °C is expressed as:

Equation 10

o

–3

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.

1.263V1.85285010–11.791.8528VTC–11.79mV/V

=+××=+×°=

23/40

STEVAL-ILL009V1 reference board AN2531

+

Table 2. Temperature limit setting using STLM20

Temperature [°C] Sensor volt age [V] ADC integer number

50 1.263 65
60 1.145 59
70 1.027 53
80 0.909 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 Ω 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

NTC

×=

RNTC

Note: V

CC

= 5 V.

VV

CCsensor

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 tem perature 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

Te mpe rature [°C] NTC resistance [kΩ] Sensor vol tage [V] ADC integer number

50 3.5 2.13 109
60 2.5 1.73 89
70 1.7 1.32 68
80 1.3 1.08 55

24/40

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
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 µs and so after each 156
µs 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

Equation 13

f

SW_PWM

Note: 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 µs, but the SPI communication takes only 4 µs (8 bit times 0.5 µs - SPI
clock is 2 MHz) and the rest (152 µs) 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.

1

t

SW_PWM

SEND_DATA

SEND_DATASW_PWM

==

value must be always same (as

–6

9.984ms1015664tLEVELSt

=××=×=

1

×

=

3–

109.984

Hz 100.16

Figure 14. Send data time diagram

25/40

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 Figu re 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 µs 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 µs), 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

Microcontroller

initialization

Enable

interrupts

Main procedure

BLINK

AR_Timmer_OF

interrupt after

each 156 µs

All DATA

are sent

Y

Time base

ON

Return

SPI interrupt

N

All DATA are sent

YES

Return

AM00296

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 level s
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 Ena ble (OE) pin.

26/40

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 nor ma l 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

Time base 156 µs

?

Y

Counter_SW ++

Time1 = 10 ms

64 x 156 µs

N

1

N

Y

Read brightness

from potentiometer

P2 (digital value

from ADC)

Time1 = 0

1

Time1 = 2.55 s

255 x 64 x156 µs

N

Time3 = 200 ms

20 x 64 x156 µs

2

Y

Time2 = 0

Temperature

Limit > measured

value

N

Increase bright

about 1 step

Time3 = 0

Startup = OFF

Negative

temperature

Y

coeficient

Decrease bright

about 1 step

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

27/40

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). 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 µs 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

Mode changed

N

MODE 1

N

MODE 2

N

Y

Set starting

conditions

Y

Set RED bright

Set DATA_blink1
Set DATA_blink2

Y

Set GREEN bright

Set DATA_blink1
Set DATA_blink2

3

MODE 3

N

MODE 4

N

MODE 5

N

Y

Set BLUE bright

Set DATA_blink1
Set DATA_blink2

Y

Set manual color

Set DATA_blink1
Set DATA_blink2

Y

Startup = ON

Set auto color

Set DATA_blink1
Set DATA_blink2

Overtemperature

3

28/40

4

AM00298

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.

Figure 19. Blink function flowchart - third part

4

Y

MODE 6

N

Default

Counter_SW = 64

N

Write to the SPI

Register
SPIDR = DATA_blink1
SPIDR = DATA_blink2

Return

Blink procedure

starts again

Set WHITE color

Set DATA_blink1
Set DATA_blink2

Y

Counter_SW = 0

AM00299

29/40

STEVAL-ILL009V5 reference board AN2531

9 STEVAL-ILL009V5 reference board

STEVAL-ILL009V5 reference board shown in Figure 20 was designed in order to promote
the new DC/DC con verter ST1S10 and the new LED drivers S TP04CM05 and STP08CP05.
Thanks to the ST1S10 DC/DC converter the size of the inductor is decreased (compare

Figure 1 and Figure 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 STEV AL-ILL009V1. The
input voltage for t he STEVAL-ILL009V5 ranges from 7 V to 18 V. The new LED drivers allow
faster communications and higher output voltage. Other design features such as SW,
brightness and color regulation, microcontroller, temperature protection, are identical on
STEVAL-ILL009V1 and STEVAL_ILL009V5. Their features are described in Chapter 8.

The ST1S10 is a high efficiency step down PWM current mode switching regulator capable
of providing up to 3 A of output current. The device operates with an input supply range from
2,5 V to 18 V. It operates either at a 900 kHz fixed frequency or can be synchronized to an
external clock (from 400 kHz to 1,2 MHz). The high switching frequency allows the use of
tiny SMD external components, while the integrated synchronous rectifier eliminates the
need for a Schottky diode. The ST1S10 provides excellent transient response, and is fully
protected against thermal overheating, switching over current and output short circuit. For
more information see the ST1S10 Datasheet.

The STP04CM05 is a high-power LED driver and 4-bit shift register designed for Power LED
applications. Four regulated constant current sources are designed to provide 80 - 400 mA
current to drive high power LEDs. The STP04CM05 guarantees 20 V output driving
capability, allowing users to connect more LEDs in series. The high clock frequency, 30
MHz, also satisfies the system requirements which include high volume data transmission.
The STP04CM05 is backward compatible with the STP04CM596.

The STP08CP05 is a monolithic, low voltage, low current, power 8-bit shift register designed
for LED panel displays. Eight regulated constant current sources are designed to provide
5 - 100 mA current to drive the LEDs, the output current setup time is 11 ns (typ), thus
improvi n g the system performance. The STP08CP05 guarantee s a 20V output dri ving
capability and high volume data transmission with clock frequency 30 MHz as well as the
STP04CM05.

Figure 20. STEVAL-ILL009V5 reference board

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AN2531 STEVAL-ILL009V5 refere nce board

The STEVAL-ILL009V5 has the following differences to compare with the STEVAL­ILL009V1:

●

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.

9.1 STEVAL-ILL009V5 schematic diagram

Figure 21 shows power supply schematic diagram. Basically, there are two parts. The first

one is a very simple linear DC/DC converter using the L78L05ACD with output voltage 5 V
used for supplying microcontroller and LED drivers. The second one is a step down
converter using monolithic, synchronous, switching DC/DC converter ST1S10 . The diode
D10 protects the application against input voltage rev ersion and Transil D9 protects the
ST1S10 against over voltage. The schematic diagram with LED drivers and microcontroller
is not shown in this chapter, because it was already introduced in Figure12. There is only
small difference, because the new LED drivers STP04CM05 and STP08CP05 instead the
STP04CM596 and STP08CL596 are used on the STEVAL-ILL009V5.

Figure 21. STEVAL-ILL009V5 power sources schematic diagram

V

C8

100 nF

P_GND

CC

+

+
100 µF

/ 16 V

SW

FB

C10

7

3

COILCRAFT
MSS1038-382NLB

3.8 µH / 6 A

INPUT VOLTAGE
FROM 7 V UP TO 18 V

J1 CON3

1
2

3

STPS340U

SMAJ15A-TR

D10

IO5 L78L05A CD

8

V

IN

GND

2

GND

3 6 7

6
2

1

GND

V
EN

V

GND

C9
100 nF

+

+

C13

47 µF / 35 V

D9

4.7 µF / 25 V
AVX: 12063D475MAT2A

C18

100 nF

C19

1

V

OUT

NC5NC

4

IO6S T1S10

T1

IN_SW

A_GND

N_A

SYN

4

5

8

R7
390 Ω

D8

Green LED

L1

3.8 µH
R9

13 KΩ

R11

3 KΩ

V

DD

C14

+

+

C15
22 µF

/ 10 V

100 µF / 16 V

AVX: 1206ZD226MAT2A

AM00261

31/40

STEVAL-ILL009V5 reference board AN2531

9.2 Bill of material

Table 4. STEVAL-ILL009V5 bill of material

Item Quantity Reference Part Note Ordering code

1 1 CONNECTOR1 ICC 10 PIN
2 1 CONNECTOR2 CON 30 PIN
3 2 C1,C6 10 nF Ceramic SMD1206

48

5 2 C10, C14 100 µF / 16 V Electrolytic SMD
6 1 C13 47 µF / 35 V Electrolytic SMD
7 1 C15 22 µF / 10 V Ceramic SMD1206 AVX:1206ZD226MAT2A
8 1 C19 4.7 µF / 25 V Ceramic SMD1206 AVX:12063D475MAT2A

97

10 1 D8 Green LED SMD LED 1206
11 1 D9 SMAJ15A-TR ST - Transil SMAJ15A-TR
12 1 D10 STPS340U ST - diode STPS340U

13 8

C2, C3, C4, C5, C7,
C8, C9, C18

D1, D2, D3, D4, D5,
D6, D7

D11, D12, D13, D14,
D15, D16, D17, D18

100 nF Ceramic SMD1206

Red LED OSRAM red LED Mini TOPLED LS M670-H2K1-1

BAT46 ST - Schottky diode BAT46JFILM

14 1 IO1 ST7FLITE09 ST - microcontroller ST7FLITE09Y0M6
15 2 IO2, IO3 STP04CM05 ST - LED driver STP04CM05XTTR
16 1 IO4 STP08CP05 ST - LED driver STP08CP05TTR
17 1 IO5 L78L05 ST - voltage regulator L78L05ACD
18 1 IO6 ST1S10 ST - DC/DC converter ST1S10PHR
19 1 J1 CON3 Input connector
20 1 L1 3.8 µH / 6 A Coilcraft inductor MSS1038-382NLB
21 2 P1, P2 10 KΩ Pot. with axi s
22 1 R1 3 kΩ SMD resistors 1206
23 2 R2, R3 220 Ω SMD resistors 1206
24 1 R4 4.7 KΩ SMD resistors 1206
25 1 R5 10 KΩ SMD resistors 1206
26 1 R6 470 Ω SMD resistors 1206
27 1 R7 390 Ω SMD resistors 1206
28 1 R9 13 KΩ SMD resistors 1206
29 1 R11 3 KΩ SMD resistors 1206
30 2 S1, S2 Switch Switch

32/40

AN2531 STEVAL-ILL009V3 load board

10 STEVAL-ILL009V 3 load board

The STEVAL-ILL009V3 demonst ration 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 12,
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 OST AR 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 22. STEVAL-ILL009V3

10.1 Schematic description

The schematic of the STEVAL-ILL009V3 is shown in Figure 23. 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 23). Resistor R4
represents together with the NTC resistor the voltage divider for t he 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 Ω 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.

33/40

STEVAL-ILL009V3 load board AN2531

Equation 14

0.6V3.4–4V–VV

F_RED_MAXdR

===

Equation 15

10.2 Bill of material

Table 5. STEVAL-ILL009V3 bill of material

Item Quantity Reference Part Note Ordering code

1 1 OSTAR projection module

2 1 Cable with con nector 10 lines cable SHR-10V-S-B -> JST
3 1 Heatsink SEMIC Trade 8150/50/N
4 1 Connector1 10 pins
5 1 Female Connector 1 10 pins
6 1 Connector2 30-pin connector
71 R1 0
8 2 R2, R3 1.5 Ω Through-hole 0.6 W
9 1 R4 4.7 kΩ Through-hole 0.6 W

R

diss

V

R

I

RED_LED

0.6

===

0.7

OSRAM OSTAR

Projecti on Mo dule

0.85Ω

LE ATB A2A

34/40

AN2531 STEVAL-ILL009V3 load board

Figure 23. STEVAL-ILL009V3 schematic diagram

R3

R2

1.5

1.5 Ω

5 Ω

10

U_r = Ud - Uf_red_max = 4 - 3.4 = 0.6 V

ICC

123456789

CONNECTOR1

R_diss = U/I = 06 / 0.7 = 0.85 => 0.75 Ω

R2 = R3 = 1.5 Ω R2 || R3 = 0.75 Ω

R1

0

0

R4

47 kΩ

5 V

4700 Ω

7

1R12

3

R1

G1a

G1a

8

4

5

G1b

6

G1b

11

12

13

9

B1

R2

B1

14

10

G2a

G2b

R2

G2a

G2b

19

15

B2

20

16

17

NC

B2

22

GND

24

21

23

NC

NC

Vcc

Vo

18

GND

NC

29

27

30

28

25

26

NC

Vd

Vd

NC

Vd

Vd

NTC 1.263 V for 72 ˚C

CONNECTOR2ICC

R_ntc (72 ˚C) = 1588 Ω

AM00300

35/40

STEVAL-ILL009V4 load board AN2531

11 STEVAL-ILL009V 4 load board

The STEVAL-ILL009V4 demonstration board is shown in Figure 24. This board is an option
to the STEVAL-ILL009V3. As a light source, there are four Golden DRAGON LEDs (refer to

Chapter 12, point 2) used with a maximum forward current of 350 mA. As described in
Chapter 8, the STEVA L-I LL009 V1 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 24. STEVAL-ILL009V4

36/40

AN2531 STEVAL-ILL009V4 load board

11.1 Schematic description

The schematic of the STEVAL-ILL009V4 is shown in Figure 25. The temperature limitation
of the Golden DRAGON LEDs is set to 50 °C on this board. Similar to the STEVAL­ILL009V3, 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

1.4V2.6–4V–VV

F_RED_MAXdR

Equation 17

===

11.2 Bill of material

Table 6. STEVAL-ILL009V4 bill of material

Item Quantity Reference Part Note Ordering code

1 2 G1a, G1b LTW5SM HZ-3

21 R1LRW5SM HY-1

3 1 B1 LBW5SM FX-3

4 1 C7 100 nF / 50 V Ceramic SMD1206
5 3 R4, R5, R6 10 Ω Through-hole resis tor
6 1 IO7 STLM20 ST temperature sensor STLM20W87F

R

V

R

I

RED_LED

1.4
4Ω

===

0.35

OSRAM Golden

DRAGON Green LED

OSRAM Golden

DRAGON Red LED

OSRAM Golden

DRAGON Blue LED

Q65110A5876

Q65110A4386

Q65110A4396

7 1 Connector2 30-pin connector

37/40

STEVAL-ILL009V4 load board AN2531

Figure 25. STEVAL-ILL009V4 schematic diagram

used (R4||R5||R6)

Ω

=> 3.3

Ω

3

2

1

Vo

NC

GND

V+

IO5

GND

4

5

Temperature sensor

CC

V

C7

100 nF

STLM20

30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12

11
10

9
8
7
6
5
4
3
2
1

Vd

Vd

Vd

Vd

NC

NC

CC

V

NC

Vo

NC

GND

D
N
G

NC

NC

B2

B2

G2b

G2b

G2a

G2a

R2

R2

B1

B1

G1b

G1b

G1a

G1a

R1

R1

AM00301

2

CONNECTOR

C
IC

U_r = U_d - U_f_red = 4 - 2.6 = 1.4 V

R = U_r / I = 1,4 / 0.35 = 4

R5 10R5 10

R4 10

R6 10R6 10

R1 G1a G1b B1

38/40

AN2531 Reference and related materials

12 Reference and related materials

1. OSRAM Opto Semiconductors, LE ATB A2A, Datasheet of OSTA R Projection Module;
www.osram-os.com

2. OSRAM Opto Semiconductors, Datasheet of Golden DRAGON LEDs;
www.osram-os.com

3. STM icroele ctronics, AN2141, LEDs Array Reference Board Design;
www.st.com

4. S TMicroele ctronics, STP04CM 596, 4-bit constant current for power-LED sink driver,
data-sheet; www.st.com

5. STM icroele ctronics, SMAJ, Transil, Datasheet; www.st.com

6. S TMicroele ctronics, L4973D3 .3, 3.5 A step down switching regulator, Datasheet;
www.st.com

7. S TMicroele ctronics, L78L05 , Positive voltage regulators, Datasheet; www.st.com

8. STM icroele ctronics, AN938, Designing with L4973, 3.5 A high efficiency DC-DC
converter; www.st.com

9. STMicroelectronics, STLM20, Ultra - low Current 2.4 V precision analog temperature
sensor , Da ta sh e et; www.st.com

10. STMicroelectronics, STP04CM05, 4-bit constant current for power-LED sink driver,
data-sheet; www.st.com

11. STMicroelectronics, STP08CP05, 8-bit constant current for LED sink driver, datasheet;
www.st.com

12. STMicroelectronics, ST1S10, 3A, 900 kHz, monolithic, synchronous step - down
regulator, datasheet; www.st.com.

13 Revision history

Table 7. Document revision history

Date Revision Changes

3-May-200 7 1 Initial release.

23-Sep-2008 2

Updated Introduction, Chapter 12, Figure 2 to Figure 10, Figure 12,

Figure 13, Figure 15 to Figure 17 , Figure 19, Figure 23 and
Figure 25, added Figure 21 and Chapter 9.

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AN2531

y

y

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