PHILIPS AN10579 Driving led light bars using nxp solution Datasheet

AN10579
Driving LED light bars using NXP solutions
Rev. 01 — 1 February 2007
Application note
Document information
Info
Content
Keywords
LED, LED controller, I2C, light bar, RGB, color mixing, architectural
lighting, LED lighting, LED driver, PWM, STARplug+, SMPS, power
conversion
Abstract
Description of Avago light bars, driving high brightness color LED strings
for color mixing and lighting applications using NXP Semiconductors
PCA9633 LED driver is discussed. An offline regulated power supply for
the LEDs is also included.
AN10579
NXP Semiconductors
Driving LED light bars using NXP solutions
Revision history
Rev
Date
Description
01
20070201
Application note; initial version.
Contact information
For additional information, please visit: http://www.nxp.com
For sales office addresses, please send an email to: [email protected]
AN10579_1
Application note
© NXP B.V. 2007. All rights reserved.
Rev. 01 — 1 February 2007
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Driving LED light bars using NXP solutions
1. Introduction
Light Emitting Diodes (LEDs) have been used in electronic systems for many years
primarily as indicator lights on electronic devices. Recent advances in high brightness and
color LEDs have made them suitable for a wide range of new applications. Today, LEDs
are being used in applications in cell phones and media players for fun lighting to
architectural/commercial lighting to replace conventional light sources. Key enablers
driving penetration of LED lighting is the availability of high brightness LEDs and
intelligent LED controllers. Product designers incorporating high brightness LEDs face
many challenges. Among them, thermal management, driver scheme/topology, device
matching for color balance and consistency. Manufactures and OEMs alike are starting to
make available LED modules consisting of clusters or strings of many LEDs of different
colors in single packages.
One such product family is ADJD-MJ00/ADJD-MJ10 RGB light bars from Avago
Technologies. This application note describes how NXP power solutions and intelligent
LED controllers can be used to drive the LED light bars to provide programmable color
mixing and brightness control features.
2. LED light bars
Avago RGB LED Light Source ADJD-MJ00/ADJD-MJ10 is a high performance device that
can be operated at high driving current. It comes with a plug-and-play electrical connector.
The built-in heat sink and the mechanical mounting features simplify the thermal
management of a lighting solution. This enables effective heat transfer and maintain LED
junction below maximum allowed temperature. Red, Green and Blue colors premix in the
reflector cavity to produce required color. The reflector cavity design maximizes the light
extraction as well as the color mixing. Together with closely pitched LED dice, the color
mixing is best of its class.
2.1 Electrical configuration
The light bar consists of four LED strings. Each LED string consists of ten LEDs
connected in series, except for red which consist of 10 pairs of parallel connected LEDs.
Each pair of parallel connected LEDs can be considered equivalent to a single large LED.
That is, for RED color, between R+ and R− terminal, there is an equivalent of ten
series-connected red LEDs.
The LED strings are:
Red color: Connect with R+ and R− terminals.
Green color: Connect with G1+ and G1− terminals.
Green color: Connect with G2+ and G2− terminals.
Blue color: Connect with B+ and B− terminals.
The circuit is shown in Figure 1.
AN10579_1
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Rev. 01 — 1 February 2007
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AN10579
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Driving LED light bars using NXP solutions
pin 5
G1−
pin 1
G1+
pin 6
R−
pin 2
R+
pin 7
B−
pin 3
B+
pin 8
G2−
pin 4
G2+
002aac791
Fig 1. Electrical configuration
2.2 Color configuration
The arrangement of Red, Green and Blue LEDs within the light bar is shown in Figure 2.
position 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
color G B R R G G R R B G G R R B G G R R B G G R R B G G R R B G G R R B G G R R B G G R R B G G R R B G
002aac792
Fig 2. Color arrangement
Fig 3. ADJD-MJ00, ADJD-MJ10 light bars
The three colors in the LED light source will mix to form a resultant color. Depending on
the mix ratio, any color within the color gamut of the LED can be obtained. The color
gamut of the LED light source is the triangle formed by the three colors points on the CIE
chromaticity chart. The three color points are from Red, Green and Blue LED color.
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Driving LED light bars using NXP solutions
2.3 Drive configuration
Figure 4 shows a basic drive circuit for the light bar.
A fixed voltage is applied to the positive terminal of each LED string through a resistor.
The negative terminal is connected to GND. The value of the resistor is determined by the
current needed and the input voltage, according to Equation 1:
VI – VF
R = ----------------IF
(1)
The current required for red, green and blue color LEDs are determined from the required
luminous intensity needed to obtain the color. The forward voltage drop, VF of the LED
strings is determined from the IF / VF graphs in the specification. The resistor required can
thus be calculated from Equation 1.
VI
RR
RB
RG
RG
GND
002aac793
Fig 4. Basic drive circuit for light bar
To adjust the resultant color and the overall brightness of the light bar, the intensities of
each string needs to be controllable. This can be accomplished by Pulse Width Modulated
(PWM) power switches on each channel as shown in Figure 5. While the PWM control of
LED strings can be implemented using a microcontroller or other hardware logic; using a
PCA9633 is less complex, easier to implement and provides a simpler and flexible
(scalable) design, especially, when multiple PWMs are involved.
AN10579_1
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Rev. 01 — 1 February 2007
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AN10579
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Driving LED light bars using NXP solutions
VI
RR
RB
RG
RG
BSP110
PWMR
BSH112
PWMB
PWMG
GND
002aac794
Fig 5. PWM dimming
3. The PCA9633 intelligent LED controller
3.1 Programmable RGGB/RGBA controller
The PCA9633 is an I2C-bus controlled 4-bit LED driver optimized for
Red/Green/Green/Blue (RGGB) or Red/Green/Blue/Amber (RGBA) color mixing
applications. It is equipped with four individual PWM controllers. Each LED output has its
own 8-bit resolution (256 steps) fixed frequency Individual PWM controller that operates
at 97 kHz with a duty cycle that is adjustable from 0 % to 99.6 % to allow the LED to be
set to a specific brightness value. A fifth 8-bit resolution (256 steps) Group PWM controller
has both a fixed frequency of 190 Hz and an adjustable frequency between 24 Hz to once
every 10.73 seconds with a duty cycle that is adjustable from 0 % to 99.6 % that is used to
either dim or blink all LEDs with the same value.
Each LED output can be off, on (no PWM control), set at its Individual PWM controller
value or at both Individual and Group PWM controller values. The LED output driver can
be programmed to be either open-drain with a 25 mA current sink capability at 5 V or
totem-pole with a 25 mA sink, 10 mA source capability at 5 V. The PCA9633 operates with
a supply voltage range of 2.3 V to 5.5 V and the outputs are 5.5 V tolerant.
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3.2 Functional description
The PCA9633 is configured and controlled by sending commands to the device via an
I2C-bus.
Like all I2C-bus compatible ICs, PCA9633 has the following advantages:
• Only two bus lines are required; a serial data line (SDA) and a serial clock line (SCL).
• The simple 2-wire serial I2C-bus minimizes interconnections so ICs have fewer pins
and there are not so many PCB tracks. Result: smaller and less expensive PCBs.
• Each device connected to the bus is software-addressable by a unique address.
• Multiple PCA9633 devices can be connected to the same I2C-bus without the need for
address decoders or chip select pins.
• Reduced software development time due to simple command byte sequences
needed for the control.
• Since PCA9633 supports Fast-mode Plus I2C-bus, serial, 8-bit oriented, bidirectional
data transfers can be made at up to 1 Mbit/s and is backward compatible with existing
Fast-mode and Standard-mode I2C-bus devices.
• The built-in 10× bus drive capability allows longer distance transmission, larger
number of components on a single bus needed in architectural lighting and gaming.
• Built-in PWM oscillator minimizes component count and cost.
• Allows glueless connection of external FETs for driving high brightness LED strings
and light bars.
• Special Group PWM control feature allows control of multiple units with simple
software commands.
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Rev. 01 — 1 February 2007
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Driving LED light bars using NXP solutions
3.3 Basic electrical configuration for using a PCA9633
A typical application circuit used to drive LEDs is shown in Figure 6.
5V
12 V
VDD = 2.5 V, 3.3 V or 5.0 V
I2C-BUS/SMBus
MASTER
SDA
10 kΩ
10 kΩ
10 kΩ(1)
VDD
SDA
SCL
SCL
OE
OE
LED0
LED1
LED2
LED3
PCA9633
A0
A1
A2
A3
A4
A5
A6
VSS
002aab286
(1) OE requires pull-up resistor if control signal from the master is open-drain.
Fig 6. PCA9633 typical application
The PCA9633 acts like an I2C-bus slave. The I2C-bus master configures the settings for
the 4 PWMs and the LED outputs by sending command bytes to the PCA9633 via the
2-wire I2C-bus. For detailed information on the PCA9633 including register definition and
command set, refer to the PCA9633 data sheet.
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Application note
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Rev. 01 — 1 February 2007
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AN10579
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Driving LED light bars using NXP solutions
3.4 Driving light bars with a PCA9633
Each LED string in the ADJD-MJ00/ADJD-MJ10 RGB light bar consists of ten LEDs
connected in series. The total forward voltage drop across the LED string for each color
for their rated DC forward current is given in Table 1.
Table 1.
Electrical characteristics
Tj = 25 °C
Color
Forward voltage, VF[1][2]
Min
Typ
Max
Testing
forward current, IF[1]
Dynamic resistance,
Rdyn[3][4]
AlInGaP red
25 V
29 V
35 V
300 mA
26 Ω
InGaN green G1
30 V
35 V
45 V
150 mA
31 Ω
InGaN green G2
30 V
35 V
45 V
150 mA
31 Ω
InGaN blue
30 V
35 V
45 V
150 mA
31 Ω
[1]
Per individual string.
[2]
VF tolerance is ±1.0 V.
[3]
Measured at Tj = 25 °C, applicable from IF = 50 mA onwards.
[4]
Dynamic resistance is the inverse slope of the forward current versus forward voltage characteristic.
A DC supply rail of 45 V or greater is needed to drive the LED strings.
While many power converter solutions are available in the market, normally the PWMs are
not offered as a part of the solution.
An application circuit for driving the LED strings using the PCA9633 PWMs is shown in
Figure 7.
The PCA9633 LED output drivers are 5.5 V only tolerant and can sink up to 25 mA at 5 V
and source 10 mA. External switching FETs are used to drive the LED strings. These
FETs must be able to switch the currents listed in Table 1 and also their drain voltages
must be able to withstand 45 V minimum.
When external FETs are used with the LED output pins of a PCA9633, output polarity
inversion is needed. PCA9633 incorporates INVRT bit (MODE2 register) to accomplish
this. For driving N-type FETs as shown in Figure 5, the INVRT and the OUTDRV bits must
both be set to logic 1.
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Driving LED light bars using NXP solutions
LED supply = 45 V
RR
RB
RG
RG
VDD = 5 V
I2C-BUS/SMBus
10 kΩ
10 kΩ
BSP110
10 kΩ(1)
VDD
MASTER
SDA
SDA
LED0
SCL
SCL
LED1
BSH112
LED2
OE
LED3
OE
PCA9633
A0
A1
A2
A3
A4
A5
A6
VSS
002aac795
(1) OE requires pull-up resistor if control signal from the master is open-drain.
Fig 7. PWM control of LED strings
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3.5 Individual brightness control with group dimming/blinking with
PCA9633
A 97 kHz fixed frequency signal with programmable duty cycle (8 bits, 256 steps) is used
to control individually the brightness for each LED string. On top of this signal (see
Figure 8), one of the following signals can be superimposed (this signal can be applied to
the 4 LED outputs):
• A lower 190 Hz fixed frequency signal with programmable duty cycle (8 bits,
256 steps) is used to provide a global brightness control.
• A programmable frequency signal from 24 Hz to 1⁄10.73 Hz (8 bits, 256 steps) with
programmable duty cycle (8 bits, 256 steps) is used to provide a global blinking
control.
1
2
3
4
5
6
7
8
9 10 11 12
507
508
509
510
511
512
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
9 10 11
Brightness Control signal (LEDn)
N × 40 ns
with N = (0 to 255)
(PWMx Register)
M × 256 × 2 × 40 ns
with M = (0 to 255)
(GRPPWM Register)
256 × 40 ns = 10.24 µs
(97.6 kHz)
Group Dimming signal
256 × 2 × 256 × 40 ns = 5.24 ms (190.7 Hz)
1
2
3
4
5
6
7
8
resulting Brightness + Group Dimming signal
002aab417
Minimum pulse width for LEDn Brightness Control is 40 ns.
Minimum pulse width for Group Dimming is 20.48 µs.
When M = 1 (GRPPWM register value), the resulting LEDn Brightness Control + Group Dimming signal will have 2 pulses
of the LED Brightness Control signal (pulse width = N × 40 ns, with ‘N’ defined in PWMx register).
This resulting Brightness + Group Dimming signal above shows a resulting Control signal with M = 4 (8 pulses).
Fig 8. Brightness + Group Dimming signals
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3.6 Color mixing and control
Color mixing is based on the RGB additive color model as shown in Figure 9.
RGB model uses additive color mixing, because it describes what kind of light needs to be
emitted to produce a given color.
002aac796
Fig 9. The RGB color model
Various ratios of the emitted light for the 3 colors determine the resulting color.
Human eye sees the sum of primary colors’ average brightness:
X % Red + Y % Green + Z % Blue
Brightness of each color LED string is adjusted using the individual PWMs on the
PCA9633. Figure 10 shows an example waveform for color mixing using PWMs.
voltage on red LED driver
ONRED
voltage on green LED driver
ONGREEN
<Ired>
<Igreen>
voltage on blue LED driver
ONBLUE
<Iblue>
frequency > 80 Hz to
100 Hz
resulting color
002aac797
Fig 10. PWM waveforms for LED color mixing
Brightness for each primary color (desired amount of each primary color) is controlled with
the duty cycle of PWMs. To perform color mixing the frequency of PWM should be high
enough so that the human eye does not see the ON/OFF phases that could result in
unwanted flicker.
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Driving LED light bars using NXP solutions
4. NXP power solutions for LED supply
As mentioned earlier, a DC supply rail of 45 V or greater is needed to drive the LED
strings used in the Light bars. This is best done using an offline power supply. NXP's
highly efficient STARplug+ range of controller ICs for low-power switched mode power
supplies (SMPSs) are well-suited for this application. STARplug+ products operate directly
from rectified universal mains supplies: 80 V to 276 V. Essentially turnkey solutions, they
dramatically cut design-in time for new power supplies in many applications.
STARplug+ devices are manufactured using NXP's high-voltage EZ-HV process. This
technology allows analog, digital and power circuitry to be implemented on the same chip.
Combined with a low-voltage BiCMOS process, it enables low-power, low-cost and
extremely compact solutions for power plugs and small supplies including power supply
for LED light bars. All STARplug+ devices feature an integrated power switch, reducing
the external component count and bill of materials.
Figure 11 shows one such power supply that provides 45 V for the LED light bar. The
120 V AC input voltage is rectified by a full bridge. A small filter or smoothing capacitor is
used to hold the rectified voltage to approximately +170 VDC. The unregulated 170 VDC is
connected to the input of the STARplug+ family switched mode controller chip that is
configured for buck mode operation.
For more detailed information on NXP’s power conversion solutions go to:
http://www.nxp.com/products/power_management/conversion/starplug/index.html
120 VAC
VI
C
DRAIN
AUX
VCC
D2
TEA152x
RC
REG
GND
Rosc
oscillator
Cosc
RREG1
SOURCE
regulation
CVCC
supply
RSOURCE
RREG2
OCP
L1
RAUX
demag
D1
output selection
Co
Z1
45 V
LED supply
002aac798
Fig 11. Offline LED power supply using STARplug+ fly-back converter
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5. Summary
The PCA9633 LED controller can be used as a companion chip for providing a driver
controller and color mixing capabilities for LED strings like the Avago
ADJD-MJ00/ADJD-MJ10 RGB light bars. This application note outlined the capabilities of
these devices and discussed how effective and programmable color mixing can be
achieved with minimal software effort.
6. Additional information
Detailed information on PCA family of LED blinkers, dimmers, controllers and other
I2C-bus products can be found at the NXP Semiconductors website:
http://www.nxp.com/products/interface_control/i2c/
For more detailed information on NXP Semiconductors power conversion solutions go to:
http://www.nxp.com/products/power_management/conversion/starplug/index.html
7. Abbreviations
Table 2.
Abbreviations
Acronym
Description
BiCMOS
Bipolar Complementary Metal Oxide Semiconductor
CIE
Commission Internationale de l'Eclairage (International Commission on Illumination)
FET
Field-Effect Transistor
IC
Integrated Circuit
I2C-bus
Inter-Integrated Circuit bus
LED
Light Emitting Diode
PCB
Printed-Circuit Board
PWM
Pulse Width Modulator
RGB
Red/Green/Blue
SMPS
Switched Mode Power Supply
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Rev. 01 — 1 February 2007
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Driving LED light bars using NXP solutions
8. Legal information
8.1
Definitions
Draft — The document is a draft version only. The content is still under
internal review and subject to formal approval, which may result in
modifications or additions. NXP Semiconductors does not give any
representations or warranties as to the accuracy or completeness of
information included herein and shall have no liability for the consequences of
use of such information.
8.2
Suitability for use — NXP Semiconductors products are not designed,
authorized or warranted to be suitable for use in medical, military, aircraft,
space or life support equipment, nor in applications where failure or
malfunction of a NXP Semiconductors product can reasonably be expected to
result in personal injury, death or severe property or environmental damage.
NXP Semiconductors accepts no liability for inclusion and/or use of NXP
Semiconductors products in such equipment or applications and therefore
such inclusion and/or use is at the customer’s own risk.
Applications — Applications that are described herein for any of these
products are for illustrative purposes only. NXP Semiconductors makes no
representation or warranty that such applications will be suitable for the
specified use without further testing or modification.
Disclaimers
General — Information in this document is believed to be accurate and
reliable. However, NXP Semiconductors does not give any representations or
warranties, expressed or implied, as to the accuracy or completeness of such
information and shall have no liability for the consequences of use of such
information.
Right to make changes — NXP Semiconductors reserves the right to make
changes to information published in this document, including without
limitation specifications and product descriptions, at any time and without
notice. This document supersedes and replaces all information supplied prior
to the publication hereof.
8.3
Trademarks
Notice: All referenced brands, product names, service names and trademarks
are the property of their respective owners.
I2C-bus — logo is a trademark of NXP B.V.
STARplug+ — is a trademark of NXP B.V.
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9. Contents
1
2
2.1
2.2
2.3
3
3.1
3.2
3.3
3.4
3.5
3.6
4
5
6
7
8
8.1
8.2
8.3
9
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
LED light bars . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Electrical configuration . . . . . . . . . . . . . . . . . . . 3
Color configuration . . . . . . . . . . . . . . . . . . . . . . 4
Drive configuration . . . . . . . . . . . . . . . . . . . . . . 5
The PCA9633 intelligent LED controller . . . . . 6
Programmable RGGB/RGBA controller . . . . . . 6
Functional description. . . . . . . . . . . . . . . . . . . . 7
Basic electrical configuration for using
a PCA9633 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Driving light bars with a PCA9633 . . . . . . . . . . 9
Individual brightness control with group
dimming/blinking with PCA9633 . . . . . . . . . . . 11
Color mixing and control . . . . . . . . . . . . . . . . . 12
NXP power solutions for LED supply . . . . . . 13
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Additional information. . . . . . . . . . . . . . . . . . . 14
Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Legal information. . . . . . . . . . . . . . . . . . . . . . . 15
Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Disclaimers . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Trademarks. . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Please be aware that important notices concerning this document and the product(s)
described herein, have been included in section ‘Legal information’.
© NXP B.V. 2007.
All rights reserved.
For more information, please visit: http://www.nxp.com
For sales office addresses, please send an email to: [email protected]
Date of release: 1 February 2007
Document identifier: AN10579_1