cd00157323

AN2531
Application 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 ® Projection Module (refer to Chapter 12, point 1) has ordering code STEVALILL009V3 and the second one with the Golden DRAGON ® LEDs (refer to Chapter 12,
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.
September 2008
STEVAL-ILL009V1 reference board
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 material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
8.5
Design calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
8.6
9
10
2/40
8.5.1
LED supply voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
8.5.2
Temperature protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
8.5.3
SW PWM frequency calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
STEVAL-ILL009V5 reference board . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.1
STEVAL-ILL009V5 schematic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . 31
9.2
Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
STEVAL-ILL009V3 load board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
10.1
Schematic description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
10.2
Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
AN2531
11
Contents
STEVAL-ILL009V4 load board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
11.1
Schematic description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
11.2
Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
12
Reference and related materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
13
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3/40
List of tables
AN2531
List of tables
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6.
Table 7.
4/40
BOM - STEVAL-ILL009V1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Temperature limit setting using STLM20 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Temperature limit setting using NTC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
STEVAL-ILL009V5 bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
STEVAL-ILL009V3 bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
STEVAL-ILL009V4 bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
AN2531
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.
Figure 24.
Figure 25.
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-ILL009V5 reference board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
STEVAL-ILL009V5 power sources schematic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
STEVAL-ILL009V3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
STEVAL-ILL009V3 schematic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
STEVAL-ILL009V4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
STEVAL-ILL009V4 schematic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
5/40
Driving concept for RGB LEDs
1
AN2531
Driving concept for RGB LEDs
RGB refers to the three primary colors, red, green, and blue. Different colors can be
generated by controlling the power to each LED. In this application, the microcontroller
provides three software PWM signals (principle is described below in Chapter 4) for LED
drivers STP04CM596 so the color can be regulated.
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
LED supply
voltage
IC supply
voltage
STP04CM596
Temperature sensor
Full color pixel
Constant
current
CONTROL PANEL
Micro
MODE
COLOR
SPI
Control
and
logic
part
I - reg.
AM00285
6/40
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 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.
Figure 3.
LED driver connection - serial configuration
Serial connection
SPI
Micro
STP04CM596
Control
and
logic
part
SPI
STP04CM596
Control
and
logic
part
LED supply
voltage
AM00286
7/40
How to drive many LEDs
Figure 4.
AN2531
LED driver connection - parallel configuration
SPI
Micro
STP04CM596
Control
and
logic
part
Parallel connection
STP04CM596
Control
and
logic
part
LED supply
voltage
AM00287
8/40
AN2531
3
How to set high current for LEDs
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
AM00288
9/40
Color control - software modulation
4
AN2531
Color control - software modulation
Software control modulation allows adjusting power to each channel of the STP04CM596
driver (i.e. LED brightness). Figure 6 explains the principle showing an example of how to
set an 8% duty cycle for red, 28% duty cycle for blue, 6% duty cycle for green and 98% duty
cycle for a fourth LED. 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
0000 1111 or new data
LEVELS
T SEND_DATA
Output 1
t
8 % duty cycle
t
Output 2
28 duty cycle
t
Output 3
6 % duty cycle
t
Output 4
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 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
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 =
1
fSW_PWM
Equation 2
t SEND_DATA =
t SW_PWM
LEVELS
Equation 3
LEVELS =
fSW_PWM
1
× t SEND_DATA
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.
11/40
Power dissipation
5
AN2531
Power dissipation
The maximum power dissipation can be calculated with ambient temperature and thermal
resistance of the chip. The thermal resistance depends on the type of package and can be
found together with maximum junction temperature in the datasheet. The maximum
allowable power consumption without a heatsink is calculated as follows:
Equation 6
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].
12/40
)
AN2531
Power dissipation
Figure 7.
RGB LED configuration
STP04CM596
Rext
I-REG
Vf_red
Vc
Vo
Vf_blue
Vo
Vf_green
Vo
Vf_green
Vo
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
SPI
Full color pixel
Lp
Control
and
logic
part
Lp
Lp
Lp
Over voltage
AM00291
14/40
AN2531
6.2
Over voltage protection
Type of solutions
Figure 9 shows possible types of over voltage protection. The first solution proposes
a Transil™ or a Zener diode connected between each channel of the LED driver and
ground. Unidirectional Transils with break down voltage lower than 16 V such as the SMAJ
Transil family (refer to Chapter 12, point 5) can be used.
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
4 V at 3 A
Lp
Temperature sensor
STP04CM596 Maximum output
voltage 16 V
Full color pixel
SPI
Lp
Control
and
logic
part
3
Lp
Lp
Lp
D
1
2
Transil
Zener
diode
4
Zener
diode
AM00292
15/40
LED temperature protection
7
AN2531
LED temperature protection
The STEVAL-009V1 was designed for high power RGB LEDs with a nominal power even
higher then ten watts. As the lifetime of LEDs significantly decreases with temperature, the
proper temperature management must be implemented to check and limit its maximum
values.
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
R
Micro
NTC
AM00293
16/40
AN2531
8
STEVAL-ILL009V1 reference board
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:
8.1
●
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.
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). 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.
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-ILL009V1 as a step by
step guide in order to quickly start with the evaluation.
Note:
18/40
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.
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.
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.
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.
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.
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.
Note:
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.
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). 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 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
20/40
P1
VCC
P2
10 KΩ
10 KΩ V
CC
Brightness
Switch
S1
R4
VCC
C7
100 nF
4.7 KΩ
Color
C1
10 nF
C5
100 nF
R6 470
VCC
9 75 3 1
16
15
14
13
12
11
10
9
S2
R5 10 KΩ
SWITCH
CONNECTOR1
ICC
VCC
ST7FLITE09
LI
VSS
PA0
VDD
PA1
RESET PA2
AIN0
NC
SCK
NC
AIN2ICCDATA
MOSI ICCCLK
CLKIN
PA7
IO1
10 8 6 4 2
1
2
3
4
5
6
7
8
C6
10 nF
VDD
R_ext
SDO
/OE
NC
OUT3
OUT2
NC
VDD
R_ext
SDO
/OE
NC
OUT3
OUT2
NC
16
15
14
13
12
11
10
9
VCC
D18 B AT 46
D17 B AT 46
D16 B AT 46
D15 B AT 46
D14 B AT 46
D13 B AT 46
D12 B AT 46
D11 B AT 46
PROTECTION
STP04CM596
GND
GND
SDI
CLK
/LE
OUT0
OUT1
NC
IO3
Vd
STP08CL596
VDD
GND
SDI
R-EXT
CLK
SDO
/LE
/OE
OUT0 OUT7
OUT1 OUT6
OUT2 OUT5
OUT3 OUT4
IO4
LED1 - GREEN LED CONTROL
LED0 - RED LED CONTROL
INFORMATION SIGNALS
LED5
LED6
LED4
LED3
LED2
LED1
LED0
220
R3
1
2
3
4
5
6
7
8
CON
CONN ECTOR2
LED6 - WHITE COLOR
LED5 - OVER TEMPERATURE
LED4 - AUTOMATIC COLOR CONTROL
16
15
14
13
12
11
10
9
C4 100 nF
LED3 - MANUAL COLOR CONTROL
220
R2
1
2
3
4
5
6
7
8
VCC
LED2 - BLUE LED CONTROL
16
15
14
13
12
11
10
9
C3 100 nF
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
STP04CM596
GND
GND
SDI
CLK
/LE
OUT0
OUT1
NC
IO2
VCC
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
1
2
3
4
5
6
7
8
C2 100 nF
3 KΩ
R1
AM00294
VCC
STEVAL-ILL009V1 reference board
AN2531
Figure 12. STEVAL-ILL009V1 schematics - LED drivers part
1
2
3
J1 CON3
INPUT VOLTAGE
FROM 8 UP TO 30 V
C13
470 µF / 35 V
D9
SMAJ33A-TR
+
C12
100 nF
C16
2,7 nF
18
19
1
8 9
6
7
5
SYNC
20
1
10
13
100 nF
OUT
BOOT
VFB
4 5 6 7 14151617
C2
C20
22 nF
R10
9.1 kΩ
12 11
C14
4700 µF / 10 V +
L1
150 µF
C15
100 nF
DMT2-149-3.8L
100 nF COILCRAFT
C21
D8
Green LED
390 Ω
R7
D10
STPS5L60
C11
C10
33 µF /
35 V
IO6
L4973D3.3
100 nF
C8
VCC
2
V3.3
GND GND GND GND OUT 3
COMP INH GND GND GND GND
SS
VCC VCC
OSC
2 3
C18 C19
100 nF 220 pF
C17
100 nF
R8
20 kΩ
100 nF
C9
VOUT
L78L05ACD
GND GND
GND GND INHIB
IN
IO5
8 V
R11
6. 2 kΩ
R9
1.3 kΩ
AM00295
Vd
AN2531
STEVAL-ILL009V1 reference board
Figure 13. STEVAL-ILL009V1 power sources schematic
21/40
STEVAL-ILL009V1 reference board
8.4
Bill of material
Table 1.
BOM - STEVAL-ILL009V1
Item Qty
Reference
AN2531
Part
Note
Ordering code
1
1
CONNECTOR1
ICC
10 PIN
2
1
CONNECTOR2
CON
30 PIN
3
2
C1, C6
10 nF
Ceramic SMD1206
4
13
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 - diode
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 regulator
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
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
DMT2-149-3.8L
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
VF = Vd
R11
R11 + R 9
Where:
VF……. Converter feedback input - > 3.3 V
Vd …… LED supply voltage
--> 4 V
From Equation 9 below resulting R9 = 1300 Ω (R11 is chosen 6.2 kΩ)
Equation 9
R9 = R11
8.5.2
Vd – VF
4 – 3.3
= 6.2 ×
= 1.3KΩ
VF
3.3
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
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.
23/40
STEVAL-ILL009V1 reference board
Table 2.
AN2531
Temperature limit setting using STLM20
Temperature [°C]
Sensor voltage [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
Vsensor = VCC ×
Note:
NTC
NTC + R
VCC = 5 V.
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.
24/40
Temperature limit setting using NTC
Temperature [°C]
NTC resistance [kΩ]
Sensor voltage [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
AN2531
8.5.3
STEVAL-ILL009V1 reference board
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 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
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 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.
Figure 14. Send data time diagram
25/40
STEVAL-ILL009V1 reference board
8.6
AN2531
Software
The software is written in C language with several modules, but the most important files for
proper operation of the STEVAL-ILL009V1 reference board are the following:
Note:
●
main.c
●
blink.c
●
pwm_ar_timer_12bit.c
●
spi.c
●
adc_8bit.c
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 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
AR_Timmer_OF
interrupt after
each 156 µs
All DATA
are sent
N
All DATA are sent
YES
Y
Time base
ON
Main procedure
BLINK
SPI interrupt
Return
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 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.
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 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
1
Start
BLINK
Time1 = 2.55 s
N
Time base 156 µs
?
Time2 = 0
N
Y
Temperature
Limit > measured
value
Counter_SW ++
N
Increase bright
about 1 step
Y
Time1 = 10 ms
64 x 156 µs
N
Y
255 x 64 x156 µs
Read brightness
from potentiometer
P2 (digital value
from ADC)
Y
Negative
temperature
coeficient
Decrease bright
about 1 step
Time3 = 200 ms
20 x 64 x156 µs
Time3 = 0
Time1 = 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
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
3
Set bright
PWM on OE pin
MODE 3
Y
Set BLUE bright
Mode changed
Y
Set DATA_blink1
Set DATA_blink2
N
Set starting
conditions
N
MODE 4
Y
Set manual color
Y
MODE 1
Set DATA_blink1
Set DATA_blink2
N
Set RED bright
N
Set DATA_blink1
Set DATA_blink2
MODE 5
Startup = ON
Y
MODE 2
Set GREEN bright
N
Set auto color
3
Overtemperature
Set DATA_blink1
Set DATA_blink2
Set DATA_blink1
Set DATA_blink2
N
Y
4
AM00298
28/40
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
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
AM00299
29/40
STEVAL-ILL009V5 reference board
9
AN2531
STEVAL-ILL009V5 reference board
STEVAL-ILL009V5 reference board shown in Figure 20 was designed in order to promote
the new DC/DC converter ST1S10 and the new LED drivers STP04CM05 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 STEVALILL009V5 has 120 mm x 47 mm instead of 151 mm x 47 mm for the STEVAL-ILL009V1. The
input voltage for the STEVAL-ILL009V5 ranges from 7 V to 18 V. The new LED drivers allow
faster communications and higher output voltage. 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
improving the system performance. The STP08CP05 guarantees a 20V output driving
capability and high volume data transmission with clock frequency 30 MHz as well as the
STP04CM05.
Figure 20. STEVAL-ILL009V5 reference board
30/40
AN2531
STEVAL-ILL009V5 reference board
The STEVAL-ILL009V5 has the following differences to compare with the STEVALILL009V1:
9.1
●
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.
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 reversion 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 Figure 12. 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
IO5
8 V
IN
VCC
L78L05A CD
1
VOUT
GND GND
GND
GND NC NC
2 3 6 7 4
5
C9
100 nF
R7
C8
100 nF
390 Ω
C10
+
100 µF
/ 16 V
D8
Green LED
INPUT VOLTAGE
VDD
FROM 7 V UP TO 18 V
COILCRAFT
J1 CON3
1
2
3
MSS1038-382NLB
IO6S
D10
T1S10
T1
6 V
SW 7
IN_SW
2 EN
1 V
FB 3
A_GND
N_A
P_GND
SYN
5 4 8
STPS340U
+ C13
47 µF / 35 V
3.8 µH / 6 A
L1
3.8 µH
R9
13 KΩ
C15
100 nF
D9
C14
+
C18
100 µF / 16 V
22 µF
/ 10 V
AVX: 1206ZD226MAT2A
3 KΩ
R11
SMAJ15A-T R
C19
4.7 µF / 25 V
AVX: 12063D475MAT2A
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
4
8
C2, C3, C4, C5, C7,
C8, C9, C18
100 nF
Ceramic SMD1206
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
9
7
D1, D2, D3, D4, D5,
D6, D7
Red LED
OSRAM red LED Mini TOPLED LS M670-H2K1-1
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
D11, D12, D13, D14,
BAT46
D15, D16, D17, D18
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
21
2
P1, P2
10 KΩ
Pot. with axis
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
MSS1038-382NLB
AN2531
10
STEVAL-ILL009V3 load board
STEVAL-ILL009V3 load board
The STEVAL-ILL009V3 demonstration board is shown in Figure 22. This board should be
connected through the 30-pin connector to the STEVAL-ILL009V1 control board to be able
to show the light effect with the board. The OSTAR projection module (refer to Chapter 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 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 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 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 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
VR = Vd – VF_RED_MAX = 4 – 3.4 = 0.6V
Equation 15
R diss =
10.2
IRED_LED
=
0.6
= 0.85Ω
0.7
Bill of material
Table 5.
STEVAL-ILL009V3 bill of material
Item Quantity
34/40
VR
Reference
Part
Note
Ordering code
1
1
OSTAR projection module
OSRAM OSTAR
Projection Module
LE ATB A2A
2
1
Cable with connector
10 lines cable
SHR-10V-S-B -> JST
3
1
Heatsink
SEMIC Trade
8150/50/N
4
1
Connector1
10 pins
5
1
Female Connector1
10 pins
6
1
Connector2
30-pin connector
7
1
R1
0
8
2
R2, R3
1.5 Ω
9
1
R4
Through-hole 0.6 W
4.7 kΩ Through-hole 0.6 W
AN2531
STEVAL-ILL009V3 load board
Figure 23. STEVAL-ILL009V3 schematic diagram
R2
R3
1. 5 Ω
10 8 6 4 2
U_r = Ud - Uf_red_max = 4 - 3.4 = 0.6 V
ICC
9 7531
1. 5 Ω
R_diss = U/I = 06 / 0.7 = 0.85 => 0.75 Ω
CONNEC TOR1
R2 = R3 = 1.5 Ω R2 || R3 = 0.75 Ω
R1
0
R4
47 kΩ
5V
4700 Ω
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
NTC
1.263 V for 72 ˚C
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
ICC
CONNECTOR2
R_ntc (72 ˚C) = 1588 Ω
AM00300
35/40
STEVAL-ILL009V4 load board
11
AN2531
STEVAL-ILL009V4 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 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 24. STEVAL-ILL009V4
36/40
AN2531
11.1
STEVAL-ILL009V4 load board
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
VR = Vd – VF_RED_MAX = 4 – 2.6 = 1.4V
Equation 17
R=
11.2
VR
IRED_LED
=
1.4
= 4Ω
0.35
Bill of material
Table 6.
STEVAL-ILL009V4 bill of material
Item
Quantity
Reference
Part
Note
Ordering code
1
2
G1a, G1b
LTW5SM HZ-3
OSRAM Golden
DRAGON Green LED
Q65110A5876
2
1
R1
LRW5SM HY-1
OSRAM Golden
DRAGON Red LED
Q65110A4386
3
1
B1
LBW5SM FX-3
OSRAM Golden
DRAGON Blue LED
Q65110A4396
4
1
C7
100 nF / 50 V
Ceramic SMD1206
5
3
R4, R5, R6
10 Ω
Through-hole resistor
6
1
IO7
STLM20
ST temperature sensor
7
1
Connector2
STLM20W87F
30-pin connector
37/40
38/40
R1
G1a
G1b
R6 10
R5 10
R4 10
B1
5
4
STLM20
Vo
GND
GND NC
V+
IO5
Temperature sensor
3
2
1
R1
R1
ICC
CONNECTOR2
AM00301
Vd
Vd
B1
R2
G2a G2b
B2
NC GND NC
NC
NC
G1a G1b
G1a G1b
B1
R2
B2
NC GND
Vo
VCC NC
Vd
Vd
G2a G2b
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
100 nF
C7
VCC
R = U_r / I = 1,4 / 0.35 = 4 Ω => 3.3 Ω used (R4||R5||R6)
U_r = U_d - U_f_red = 4 - 2.6 = 1.4 V
STEVAL-ILL009V4 load board
AN2531
Figure 25. STEVAL-ILL009V4 schematic diagram
AN2531
12
Reference and related materials
Reference and related materials
1.
OSRAM Opto Semiconductors, LE ATB A2A, Datasheet of OSTAR Projection Module;
www.osram-os.com
2.
OSRAM Opto Semiconductors, Datasheet of Golden DRAGON LEDs;
www.osram-os.com
3.
STMicroelectronics, AN2141, LEDs Array Reference Board Design;
www.st.com
4.
STMicroelectronics, STP04CM596, 4-bit constant current for power-LED sink driver,
data-sheet; www.st.com
5.
STMicroelectronics, SMAJ, Transil, Datasheet; www.st.com
6.
STMicroelectronics, L4973D3.3, 3.5 A step down switching regulator, Datasheet;
www.st.com
7.
STMicroelectronics, L78L05, Positive voltage regulators, Datasheet; www.st.com
8.
STMicroelectronics, 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, Datasheet; 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-2007
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.
39/40
AN2531
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