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Renesas Electronics assumes no liability for damages or losses occurring as a result of your noncompliance with applicable laws and regulations. This document may not be reproduced or duplicated, in any form, in whole or in part, without prior written consent of Renesas Electronics. Please contact a Renesas Electronics sales office if you have any questions regarding the information contained in this document or Renesas Electronics products, or if you have any other inquiries. (Note 1) “Renesas Electronics” as used in this document means Renesas Electronics Corporation and also includes its majorityowned subsidiaries. (Note 2) “Renesas Electronics product(s)” means any product developed or manufactured by or for Renesas Electronics. Application Note Controlling High Brightness LED by using 78K0/Ix2 This document describes a reference design for controlling a high brightness LED by using various functions mounted onto the 78K0/Ix2 microcontroller. Specifically, the document describes methods for driving a constant current and dimming LED by using the PWM output and internal analog peripherals (comparator and A/D converter) of 78K0/Ix2 microcontroller. Target devices 78K0/IY2 microcontroller 78K0/IA2 microcontroller 78K0/IB2 microcontroller Document No. U19666EJ1V0AN00 (1st edition) Date Published March 2009 NS 2009 Printed in Japan CONTENTS CHAPTER 1 INTRODUCTION............................................................................ 3 1.1 78K0/Ix2 Features for High Brightness LED Control ............................ 3 1.2 System Overview ..................................................................................... 4 CHAPTER 2 CONTROL THEORY...................................................................... 5 2.1 Buck Converter Basics............................................................................ 5 2.2 Constant Current Control Method .......................................................... 7 2.2.1 Internal comparator feedback ....................................................... 8 2.2.2 Internal A/D converter feedback ................................................. 11 2.3 Dimming Control .................................................................................... 14 2.3.1 DC dimming ................................................................................ 14 2.3.2 PWM dimming ............................................................................ 16 2.4 User Interface ......................................................................................... 17 2.4.1 Internal A/D converter control interface ...................................... 17 2.4.2 DMX512 protocol communication control interface .................... 21 2.4.3 DALI protocol communication control interface .......................... 25 APPENDIX A REFERENCE CIRCUIT DIAGRAM (EZ-0005) ........................... 27 APPENDIX B REFERENCE PARTS TABLE (EZ-0005) ................................. 29 APPENDIX C EXAMPLE INTERNAL REFERENCE VOLTAGES AND PWM OUTPUT DUTY PARAMETERS (FOR INTERNAL COMPARATOR FEEDBACK) ................................................... 31 APPENDIX D EXAMPLE A/D CONVERTER EXPECTED VALUES AND PWM OUTPUT DUTY PARAMETERS (FOR INTERNAL A/D CONVERTER FEEDBACK) ....................................................... 32 • The information in this document is current as of March, 2009. 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"Special": Transportation equipment (automobiles, trains, ships, etc.), traffic control systems, anti-disaster systems, anti-crime systems, safety equipment and medical equipment (not specifically designed for life support). "Specific": Aircraft, aerospace equipment, submersible repeaters, nuclear reactor control systems, life support systems and medical equipment for life support, etc. The quality grade of NEC Electronics products is "Standard" unless otherwise expressly specified in NEC Electronics data sheets or data books, etc. If customers wish to use NEC Electronics products in applications not intended by NEC Electronics, they must contact an NEC Electronics sales representative in advance to determine NEC Electronics' willingness to support a given application. (Note) (1) "NEC Electronics" as used in this statement means NEC Electronics Corporation and also includes its majority-owned subsidiaries. (2) "NEC Electronics products" means any product developed or manufactured by or for NEC Electronics (as defined above). M8E 02. 11-1 2 Application Note U19666EJ1V0AN CHAPTER 1 INTRODUCTION This document describes a reference design for a high brightness LED control application using the 78K0/Ix2 microcontroller. 1.1 78K0/Ix2 Features for High Brightness LED Control High brightness LED control using the 78K0/Ix2 microcontroller has the following features: • The LED constant current drive can be controlled by using a PWM timer (TMXn: n = 0, 1) and analog peripheral (comparator or A/D converter) mounted onto the 78K0/Ix2. This will help you to remove the LED driver IC. Two constant current feedback methods can be used for the 78K0/Ix2: - Comparator feedback - 10-bit A/D converter feedback • Dimming can be controlled by using a comparator or PWM timer mounted onto the 78K0/Ix2. Two LED dimming methods can be used for the 78K0/Ix2: - DC dimming by changing the internal programmable reference voltage for the comparator - PWM dimming by using the PWM timer (TMH1) • The high brightness LED be controlled by using the A/D converter or communication functions mounted onto the 78K0/Ix2. Three control methods can be used for the 78K0/Ix2: - Volume control by using the 10-bit A/D converter - DMX512 protocol communication control by using UART (78K0/IA2 and 78K0/IB2 only) - DALI protocol communication control by using UART (in DALI mode) (78K0/IA2 and 78K0/IB2 only) Remark The control method introduced in this application note can be evaluated using the 78K0/IB2 HBLED evaluation board (EZ-0005) offered by NEC Electronics. Please visit to the following website for details about the evaluation board: • URL: http://www.necel.com/micro/en/solution/lighting/index.html Application Note U19666EJ1V0AN 3 CHAPTER 1 INTRODUCTION 1.2 System Overview Figures 1-1 and 1-2 show block diagrams for three-channel LED control by using the 78K0/Ix2 microcontroller. Figure 1-1. Block Diagram of 3-Channel LED Control Using 78K0/Ix2 Microcontroller (Feedback by Comparators) DALI DMX512 16-bit TMX0,1 8-bit OSC TMH1 20 MHz Comparator CPU UART (DALI) Cnt. 40 MHz 10-bit ADC CH-1 CH-2 CMP0+ Vref Volume CH-0 PWM CMP1+ Vref CMP2+ Vref 78K0/Ix2 Microcontroller Figure 1-2. Block Diagram of 3-Channel LED Control Using 78K0/Ix2 Microcontroller (Feedback by10-bit A/D Converter) DALI DMX512 UART (DALI) OSC 20 MHz 16-bit TMX0,1 8-bit TMH1 CPU 10-bit ADC Cnt. 40 MHz PWM CH-1 CH-2 ANIx ANIx ANIx Volume 78K0/Ix2 Microcontroller 4 CH-0 Application Note U19666EJ1V0AN CHAPTER 2 CONTROL THEORY 2.1 Buck Converter Basics By using the timer and either the comparators or A/D converter integrated into 78K0/Ix2 microcontroller, constant current control is possible. This enables high brightness LED control without using a separate LED-dedicated constant current driver IC. Figure 2-1 shows the basic of buck converter configuration. Figure 2-1. Buck Converter Basics IL Vf Vi VD Vo Vs A buck converter operates using an inductor (L), a switch (SW), and a diode (D). Figure 2-2 shows an example of constant current control using a buck converter while PWM output controls the switch (SW). Application Note U19666EJ1V0AN 5 CHAPTER 2 CONTROL THEORY Figure 2-2. Constant Current Control tON tOFF tON tOFF tON PWM output 0 charge discharge charge discharge charge IL 0 When the switch (SW) is on, the voltage bias on the inductor becomes (Vi – Vo), and the current increases according to following equation: | IL(ON) | = [ (Vi – Vo) × tON ] / L While the switch (SW) is off, the current through the inductor (L) decreases according to the following equation during the off period (tOFF): | IL(OFF) | = [ (Vo – VD) × tOFF ] / L Assuming the converter operates in a steady state, the current is constant and can be calculated the following equation: | IL(ON) | = | IL(OFF) | These two periods repeat. The converter is regulated by varying the duty cycle of the power switch according to the load conditions. To achieve this, the power switch requires electronic control for proper operation. It is possible to determine the duty cycle as follows: Duty = tON / t (switching cycle (t): tON + tOFF) Duty = Vo / Vi An example of selecting an inductor (L) and a sense resistor (RS) is shown here. When using a constant current to control LEDs, the forward current must be kept constant. When detecting the forward current using a sense resistor, the sense voltage (Vs) is as follows: VS = IL × RS To drive LEDs at a better power efficiency, the sense voltage (Vs) must be minimized. In contrast, to achieve higher dimming resolution, higher sense voltage (Vs) is required. In addition, to reduce the error margin for the sense voltage, accurate sense resistors must be selected. Suppose the typical forward current of a selected LED is 300 mA. Select the sense voltage (VS) as 1.4 V during full output. The sense resistor (RS) should be 4.7 Ω (1 W). 1.4 (V) = 0.3 (A) × RS RS = 1.4 (V) / 0.3 (A) ≈ 4.7 Ω 6 Application Note U19666EJ1V0AN CHAPTER 2 CONTROL THEORY The inductor value can be decided by the following equations: VL = L × di / dt L = (Vi – VO) × Duty × t / Iripple Duty = Vo / Vi Iripple (target) < IL × 1.5 [%] To realize 8-bit resolution for switching duty when using PWM output, the 78K0/Ix2 microcontroller can output a 8 156.25 kHz PWM signal (40 MHz/2 ) from 16-bit timers X0 and X1 by using a 40 MHz clock source. So, t =1 / f =1 / 156.25 kHz For an input voltage (Vi) of 5 V, the LED forward voltage (Vf) of 3.5 V, and a sense voltage (VS) of 1.4 V, an inductor (L) larger than 140 μH is suitable for this feedback circuit. L > (Vi – VO) × Duty × t / Iripple L > (5.0 – 4.9) × (4.9/5) × (1/156250) × (1/0.3 × 1.5 % or 0.015) L > 139.38 [μ H] 2.2 Constant Current Control Method As shown in Figure 2-2, to perform control at a constant current, it is necessary to keep the sense voltage (Vs) through the sense resistor (Rs) the same as the target reference voltage. If the sense voltage (VS) is higher than the reference voltage, the PWM output duty must be reduced to reduce a mount of time that the MOSFET switch is on and the current (sense voltage). In contrast, if the sense voltage (VS) is lower than the reference voltage, the PWM output duty must be increased to increase the mount of time that the MOSFET switch is on and the current (sense voltage). To compare the sense voltage and reference voltage adjusted by controlling PWM output, a method that uses the 78K0/Ix2 comparators and one that uses the 78K0/Ix2 A/D converter are available. The features of these methods are as follows: • Comparator feedback: Because the CPU is not accessed before comparator interrupts occur, the software load can be reduced. • A/D converter feedback: Because converted values are immediately compared, the ripple of current is smaller and the dimming resolution can be higher. However, the CPU is used to perform all channel switching and comparison for A/D converter. PWM output for MOSFET switching is performed using the 16-bit timers X0 and X1. A 156.25 kHz switching frequency is available because these timers use a 40 MHz clock as a counting source with a resolution of 8 bits (40 8 MHz/2 ). Application Note U19666EJ1V0AN 7 CHAPTER 2 CONTROL THEORY 2.2.1 Internal comparator feedback The 78K0Ix2 microcontroller has three internal comparators with programmable internal voltage references, so that three channels of LEDs can be driven independently using a comparator feedback method. Specify the valid edge of the comparator interrupt to be both edges. The comparator interrupt occurs while the sense voltage (Vs) is higher or lower than the reference voltage. When this interrupt occurs, execute constant current feedback control by adjusting the PWM duty cycle. When a comparator interrupt occurs, use the CMPnF flag to compare the comparator output level with expected value to avoid misjudgment caused by noise. Set the expected level of comparator output to the high level when increasing the duty. Set the expected level to the low level when reducing the duty. By comparing the comparator output level with the expected value, changes in the duty due to unexpected noise can be avoided. Figure 2-3. Example of Internal Comparator feedback Turn to higher duty Turn to lower duty Turn to higher duty Turn to lower duty PWM output (TMXxx) Internal comparator output (CMPnF flag) Sense voltage (Vs) input Vref Change duty Change duty Change duty Change duty Figure 2-4. Example of Avoiding Misjudgment Caused by Noise A B (High) Expected level of internal comparator output B (High) (Low) (High) Internal comparator output (CMPnF flag) (Low) (Low) Sense voltage (Vs) input Vref Noise A: CMPnF does not match the expected level. Adjust the wave as noise. B: CMPnF matches the expected level. Feedback processing is required. The higher duty and lower duty parameters are stored beforehand. For the higher duty, a sense voltage over the target level is output. A lower duty causes a sense voltage under the target level. It is possible to determine these two parameters by experimenting. An example of data table based on the evaluation board (EZ-0005) is provided in Appendix C. 8 Application Note U19666EJ1V0AN CHAPTER 2 CONTROL THEORY Figure 2-5. Flowchart of Comparator Feedback (1/2) (Main processing) Reset start Initialization, start the timer X, start the comparator CH0 feedback processing CH1 feedback processing CH2 feedback processing Interface control processing (Comparator n interrupt processing: n = 0 to 2) INTCMPn interrupt processing CMPn output = expected level of comparator output? No Yes Set the CMPn interrupt mask flag, reverse expected level of comparator output, set the CHn feedback flag INTCMPn interrupt processing end Caution Feedback processing is executed according to the results of comparator interrupt processing. Remark The CHn feedback flag is used to indicate whether the PWM output changing processing is enabled or disabled. Application Note U19666EJ1V0AN 9 CHAPTER 2 CONTROL THEORY Figure 2-5. Flowchart of Comparator Feedback (2/2) (Comparator n feedback processing: n = 0 to 2) CHn feedback processing No CHn feedback flag on? Yes No Expected level of comparator = ”low”? Yes Set duty to lower level Set duty to higher level Clear the CHn feedback flag, clear the CMPn interrupt request flag, clear the CMPn interrupt mask flag CHn feedback processing end Caution Feedback processing is executed according to the results of comparator interrupt processing. Remark The CHn feedback flag is used to indicate whether the PWM output changing processing is enabled or disabled. Figure 2-6 shows the data measured using the comparator feedback. Figure 2-6. Measure Data of Sense Voltage (VS) (Comparator Feedback) Remark The circuit constants are below. • Inductor (L): 150 μH • Sense resistor (RS): 4.7 Ω • LED forward current: 300 mA 10 Application Note U19666EJ1V0AN CHAPTER 2 CONTROL THEORY 2.2.2 Internal A/D converter feedback The 78K0Ix2 microcontroller has an A/D converter that consists of up to 9 channels with a resolution of 10 bits, so that several LEDs can be driven independently using an A/D converter feedback method. If the A/D converter is set up to operate at the shortest conversion time which is 3.3 μs, feedback processing for each channel can be executed every 20 μs. The maximum and minimum target values of the A/D conversion results (the reference value for the sense voltage (Vs)) can be decided based on the detection accuracy of the target current. If the input voltage (Vi) = VDD = 5 V, the sense voltage (Vs) = 1.4 V, and the ratio to define is 2%, the target range of A/D conversion result is supposed to approximately equal to the target level ±5LSB. When the A/D conversion result is over the maximum while increasing compared with the last result, step down the duty. When the A/D conversion result becomes smaller than the minimum while decreasing compared with the last result, step up the duty. To speed up the startup period of LEDs, set the duty of PWM output to the target duty related to the target A/D converter level before starting the timer X and the A/D converter. While the A/D conversion result is almost 0, directly set the duty to the target value corresponding to the target A/D converter level. The target duty related to each target level can be determined by experimenting. An example of data table based on the evaluation board (EZ-0005) is provided in Appendix D. Figure 2-7. Example of Internal A/D Converter Feedback Set to target duty Turn to lower Turn to higher duty duty Turn to lower duty Turn to higher duty Change duty Judge by A/D conversion result PWM output (TMXxx) Not change duty Maximum Target level (reference level of sense voltage (VS )) Target range Sense voltage input (ANIx) Minimum 0 Application Note U19666EJ1V0AN 11 CHAPTER 2 CONTROL THEORY Figure 2-8. Flowchart of A/D Converter Feedback (1/2) (Main processing) Reset start Initialization, start the timer X, start the A/D converter Interface control processing (A/D Converter interrupt processing) INTAD interrupt processing Read out the A/D conversion result, set the A/D interrupt mask flag Measured CH0? Yes CH0 feedback processing No Measured CH1? No Yes CH1 feedback processing INTAD interrupt processing end 12 Application Note U19666EJ1V0AN Measured CH2? Yes CH2 feedback processing No CHAPTER 2 CONTROL THEORY Figure 2-8. Flowchart of A/D Converter Feedback (2/2) (CHn feedback processing ) CHn feedback processing Turn to the next A/D conversion channel, clear the A/D interrupt mask flag A/D conversion result ≈0? (to avoid noise and A/D conversion errors) No A/D conversion result > last result? (current increasing?) Yes Set TMXn to output the target duty No Yes No A/D conversion result > Maximum value? (over the target range?) A/D conversion result < Minimum value? (under the target range?) No Yes Yes Is it out of the range if setting the duty to lower level? No Set to the duty to lower level Yes Is it out of the range if setting the duty to higher level? Yes No Set to the duty to higher level Store the A/D conversion result as the latest one CHn feedback processing end Figure 2-9 shows the data measured using A/D converter feedback. Figure 2-9. Measure Data of Sense Voltage (VS) (A/D Converter Feedback) Remark The circuit constants are below. • Inductor (L): 150 μH • Sense resistor (RS): 4.7 Ω • LED forward current: 300 mA Application Note U19666EJ1V0AN 13 CHAPTER 2 CONTROL THEORY 2.3 Dimming Control Dimming means change the brightness of LED. Dimming can be controlled by changing the LED forward current. Here, two dimming methods for the 78K0/Ix2 microcontroller are introduced: DC dimming and PWM dimming. 2.3.1 DC dimming (1) Dimming by changing the internal reference voltage The 78K0/Ix2 microcontroller can generate 3 internal reference voltages independently for each internal comparator, which can be divided into 32 steps. As expressed in 2.2, the 78K0/Ix2 microcontroller monitors the sense voltage (VS) and compares it to a stable reference to keep the current constant. Changing the reference voltage helps the circuit constantly keep the current as a different level. Dimming requirements depend on communication and user setting. For the comparator feedback, change the internal reference voltage of each comparator. Also change higher duty and lower duty parameters. The internal reference voltage can be changed in 32 steps in the range from 0.05 V (typ.) to 1.6 V (typ.). To increase the dimming resolution, set the sense voltage (Vs) when driving current at the maximum brightness to as high a value as possible in the range of the internal reference voltage. Figure 2-10. Flowchart of Dimming for Changing Internal Reference Voltage There is a dimming requirement of CHn Stop CMPn, change the internal reference voltage, change the PWM output duty for the constant current control, set the initial PWM output duty to 100%, start CMPn CHn dimming processing end 14 Application Note U19666EJ1V0AN CHAPTER 2 CONTROL THEORY (2) Dimming by changing the target level for the A/D conversion result The 78K0Ix2 microcontroller has an A/D converter with a resolution of 10 bits. For the A/D converter feedback, change the parameter target level. Also change the target duty. The Reference voltage for the maximum brightness is selected by considering the hardware design and the limit of the A/D converter reference voltage. The dimming step number is decided by using maximum reference voltage and error margin for the target level. To increase the dimming resolution, set the sense voltage (Vs) when driving current at the maximum brightness to as high a value as possible within the range of voltages for which A/D conversion is possible (AVREF or less). Figure 2-11. Flowchart of DC Dimming by Changing Target Level for A/D conversion Result There is a dimming requirement of CHn Set the A/D interrupt mask flag, change the reference level of A/D conversion result , change the PWM output duty for the constant current control, clear the last A/D conversion result, set the initial PWM output duty, clear the A/D interrupt request flag, clear the A/D interrupt mask flag Set the A/D conversion channel to one of the feedback channels During feedback with A/D converter CHn dimming processing end Application Note U19666EJ1V0AN 15 CHAPTER 2 CONTROL THEORY 2.3.2 PWM dimming 78K0/Ix2 microcontroller includes a function that performs gate control for the signals output by the 16-bit timers X0 and X1 by using the output of the 8-bit timer H1. Keeping the reference voltage at the maximum level, LEDs can be dimmed in 255 steps by using the TMXn output gate function via the TMH1 output. A square PWM wave output by the 8-bit timer H1 can be set to control all 4 TMXn outputs. If TOH1 is combined with the outputs of 16-bit timers X0 and X1, the TMXn output is only enabled when the TOH1 output is at high level or low level. While using PWM dimming via TMH1, all TMX outputs will start or stop at the same time. Therefore, this method can be used to dim the LEDs of all channels at the same time. Figure 2-12. Example Timing Chart of TMX0 and TMX1 Output Gate Function via TMH1 Output TOH1 output (internal output) TMXxx output (internal output) TOXxx pin output Considering the startup speed of each channel, it seems the TMH1 output frequency should be selected to be as low as possible. However, the limitations of the human eye also affect this decision. A 100 Hz frequency is usually assumed to be sufficient for avoiding flicker, which means the frequency should be higher than 100Hz. Figure 2-13. Sense Voltage and TOXxx Output Measurement Data (PWM Dimming via TMH1 Output) TOXxx pin output Sense voltage (Vs) 16 Application Note U19666EJ1V0AN CHAPTER 2 CONTROL THEORY 2.4 User Interface The user can assign dimming requirements by using the user interface mounted onto the 78K0/Ix2 microcontroller. Three interfaces are introduced here: A/D converter control interface, DMX512 control interface, and DALI (Digital Addressable Lighting Interface) control interface 2.4.1 Internal A/D converter control interface The 78K0Ix2 microcontroller has an A/D converter that consists of up to 9 channels. Volume switches, sensors or some other analog inputs can be connected to these analog input pins as the dimming requirement trigger. Except the ones used for the feedback input, all A/D converter input pins are available. While using the A/D converter feedback, the feedback channels and the user interface channels use the same the A/D converter interrupt. This results in different flowcharts for the A/D converter interface with the comparator feedback as opposed to the A/D converter feedback. Figure 2-14. Flowchart of A/D Converter Control Interface (Comparator Feedback) (1/2) (Main processing) Reset start Initialization, start the timer X, start the comparator, start the A/D converter, start the timer 51 CH0 feedback processing Note CH1 feedback processing No te CH2 feedback processing No te Dimming processing by switching volume Note For the comparator feedback, see 2.2.1 Internal comparator feedback. Caution A/D conversion starts when the interrupt of 8-bit timer 51 occurs. LEDs are dimmed using the volume switches according to the result of A/D converter interrupt servicing. Application Note U19666EJ1V0AN 17 CHAPTER 2 CONTROL THEORY Figure 2-14. Flowchart of A/D Converter Control Interface (Comparator Feedback) (2/2) (Interrupt processing: A/D converter, 8-bit timer 51) INTAD interrupt processing INTTM51 interrupt processing Read out the A/D conversion result, set the dimming data detection status flag, stop A/D conversion Reset the A/D conversion channel, start A/D conversion INTTM51 interrupt processing end INTAD interrupt processing end (Dimming processing by switching volume) A/D interface dimming processing New dimming data received? No Yes A/D conversion result for LED CH0 control? No A/D conversion result for LED CH1 control? No A/D conversion result for LED CH2 control? Yes Yes Yes CH1 control parameter set processing CH0 control parameter set processing No CH2 control parameter set processing Clear the dimming data detection status flag A/D interface dimming processing end (CHn control parameter set processing) CHn control parameter set processing AD conversion result = 0? Yes Stop the timer X output No Based on the A/D conversion result: • Change the comparator reference voltage • Change the PWM output duty of the timer X (start the timer X) CHn control parameter set processing end Caution A/D conversion starts when the interrupt of 8-bit timer 51 occurs. LEDs are dimmed using the volume switches according to the result of A/D converter interrupt servicing. Remark The dimming data detection status flag is used to indicate whether the dimming processing by switching volume is enable or disable. 18 Application Note U19666EJ1V0AN CHAPTER 2 CONTROL THEORY Figure 2-15. Flowchart of A/D Converter Control Interface (A/D Converter Feedback) (1/2) (Main processing) Reset start Initialization, start the timer X, start the A/D conversion, start the timer 51 Main loop (Interrupt processing: 8-bit timer 51) INTTM51 interrupt processing Is the last I/F channel the I/F CH2? No Yes Turn to I/F CH0 Turn to I/F CHn+1 Clear the A/D interrupt request flag, clear the A/D interrupt mask flag INTTM51 interrupt processing end Remark I/F CHn: A/D conversion channels for LED CHn control interface Application Note U19666EJ1V0AN 19 CHAPTER 2 CONTROL THEORY Figure 2-15. Flowchart of A/D Converter Control Interface (A/D Converter Feedback) (2/2) (Interrupt processing: A/D converter) INTAD interrupt processing Read out the A/D conversion result, set the A/D interrupt mask flag A/D conversion by using F/B CH0? No Yes A/D conversion by using F/B CH1? Yes CH0 feedback processing Note A/D conversion by using F/B CH2? No No Yes CH2 feedback processing Note CH1 feedback processing Note A/D conversion by using I/F CH0? A/D conversion by using I/F CH1? No Yes Yes CH0 dimming processing No A/D conversion by using I/F CH2? No Yes CH1 dimming processing CH2 dimming processing INTAD interrupt processing end (CHn dimming processing) CHn dimming processing AD conversion result = 0? Yes Stop the timer X output No Set the A/D interrupt mask flag, based on A/D conversion result: • Change the reference level of the A/D conversion result • Change the PWM output duty for the constant current control clear the last A/D conversion result, set the initial PWM output duty, clear the A/D interrupt request flag, clear the A/D interrupt mask flag Set the A/D conversion channel to one of the feedback channels CHn dimming processing end Note For the CHn feedback processing, see 2.2.2 Internal A/D converter feedback. Remark F/B CHn: A/D conversion channels for LED CHn feedback processing I/F CHn: 20 A/D conversion channels for LED CHn control interface Application Note U19666EJ1V0AN CHAPTER 2 CONTROL THEORY 2.4.2 DMX512 protocol communication control interface The DMX data stream clocks out at a rate of 250 kHz, which means each bit is measured in 4 microseconds. The DMX512 signal is transmitted via RS485, which is the industry standard interface. The RS485 standard uses two or three wires to transmit digital HIs and LOs: • The +signal wire (+s) • The −signal wire (−s) • The 0 wire or ground wire (0 V) Figure 2-16 shows the DMX receiver hardware interface. Figure 2-16. DMX512 Receiver Hardware Interface DMX512 input signal +S RS485 Receiver 78K0/Ix2 microcontroller + Connect to RxD6 pin (UART6) −S − 0V Application Note U19666EJ1V0AN 21 CHAPTER 2 CONTROL THEORY Figure 2-17 shows the DMX timing chart. Figure 2-17. DMX512 Timing Chart MTBP IDLE Stop bits Start bit MAB 8-data bits 512 flames in all MTBF Break ••• DATA=0 Frame Width Start Code Break Remark Frame Width Channel 1 Frame Width Channel n MIN. TYP. MAX. Unit 88 88 1,000,000 μs MAB 8 μs Frame Width 44 μs Start/Data/Stop bits 4 μs MTBF 0 NS 1,000,000 μs MTBP 0 NS 1,000,000 μs NS: not specified The meanings of addresses and data freely are defined by users. For example, while the DMX512 protocol is used to control stage lighting, one lamp has several addresses and data can be defined as the brightness, position, and so on. The first byte after the start code (SC) is automatically taken as the data value for address 1, the next data value is for address 2, and so on. The slave counts the data and uses that which belongs to its address to start dimming processing. Figure 2-18 shows the flowchart of the dimming control by the DMX512 protocol communication interface. In this example, the 3 LED channels are controlled using independent address. 22 Application Note U19666EJ1V0AN CHAPTER 2 CONTROL THEORY Figure 2-18. Flowchart of Dimming Control by DMX512 Protocol Communication Interface (1/2) (Main processing) Reset start Initialization, start the timer X, start the comparator (for feedback),Note start the timer 51 (for time out), start UART6 reception (for DMX512 reception) CH0 feedback processing CH1 feedback processing Note CH2 feedback processing DMX512 dimming processing (Interrupt processing: serial interface UART6 (no error during reception, error during reception), 8-bit timer 51) INTSRE6 interrupt processing Set the break detection status flag, read out the error status, read out the receive buffer INTSRE6 interrupt processing end INTSR6 interrupt processing Save the receive data, count up the number of the receive data (up to 513) INTSR6 interrupt processing end INTTM51 interrupt processing Count up the timer out counter INTTM51 interrupt processing end Note Using the comparator feedback processing only. For the comparator feedback processing, see 2.2.1 Internal comparator feedback. For the A/D converter feedback processing, see 2.2.2 Internal A/D converter feedback. Caution Dimming processing controlled by DMX512 interface starts when the serial interface UART6 receives an error interrupt. Remark The break detection status flag is used to show that the break time of the DMX512 signal has been detected. Application Note U19666EJ1V0AN 23 CHAPTER 2 CONTROL THEORY Figure 2-18. Example Flowchart of Dimming Control by DMX512 Protocol Communication Interface (2/2) (DMX 512 dimming processing) DMX512 dimming processing No Communication idle? Yes Break detection status flag on? No Yes Start time out counting, set the during reception state flag No During reception state flag on? Yes All 513 data items received? No No Time out? Yes Yes Stop time out counting, clear the number of the reception data, set the reception completion state flag Stop time out counting, clear the number of the reception data, set the error state flag Reception completion state flag on? No Yes Target channel dimming Set the dimming completion state flag “dimming completion” or “error occurred”? dimming completion error occurred Communication line returned to Idle? No Yes Set the communication idle state flag DMX512 dimming processing end Caution Dimming processing controlled by DMX512 interface starts when the serial interface UART6 receives an error interrupt. Remark 24 The status flag is used to show that the communication status has been detected during reception. Application Note U19666EJ1V0AN CHAPTER 2 CONTROL THEORY 2.4.3 DALI protocol communication control interface The serial interface UART6 of the 78K0/Ix2 microcontroller supports a special mode for performing transmission and reception as a DALI slave. DALI stands for Digital Addressable Lighting Interface and is a royalty-free, non-proprietary, two-way, open, interoperable digital protocol. It is a standard in the United States and Europe. This protocol is used to dim multi ballasts or LEDs in a system. One system contains a maximum of 64 individual addressable slaves. The DALI protocol communicates at a rate of 1,200 Hz±10 %. The master dims and brightens slaves in 256 steps. Each step of brightness can be stored as a scene. Figure 2-19 shows the example of the DALI slave circuit by using the 78K0/Ix2 microcontroller. Figure 2-19. Example of DALI Slave Circuit by Using 78K0/Ix2 Microcontroller DALI communication line TxD6 5V 5V 11 k PS2561AL-1 PS2561AL-1 RxD6 22 m 4.7 1.2 k 330 10 k 78K0/Ix2 RD2.7S 3.3 k Remarks 1. PS2561AL-1 is a photocoupler made by NEC Electronics. 2. RD2.7S is a Zener diode made by NEC Electronics. The definitions of forward and backward message frames in the DALI communication protocol are as follows: A forward message frame that consists of 19 bits is sent from the master: − 1 start bit − 1 address byte: 1 individual or group address bit, 6 address bits, 1 selection bit − 1 data byte: 8 data bits − 2 stop bits A backward message frame that consists of 11 bits is sent from the slave: − 1 start bit − 1 data byte: 8 data bits − 2 stop bits Application Note U19666EJ1V0AN 25 CHAPTER 2 CONTROL THEORY Figure 2-20. Example of DALI Receiving Timing Chart by Using 78K0/Ix2 Microcontroller Fixed to high level Transmission pin (TxD6 pin) Start bit (1) (0) (0) Address byte (8 bits) (0) (0) (0) (0) (0) (1) (0) (0) (0) Data byte (8 bits) (0) (0) (1) (0) (1) Stop bits (2 bits) Reception pin (RxD6 pin) Received data Higher 8 bits: 00000001B Lower 8 bits: 00000101B Reception buffer (RXBDL register) Reception completion interrupt (INTSR6 signal) Figure 2-20. Example of DALI Transmitting Timing Chart by Using 78K0/Ix2 Microcontroller Transmission buffer (TXB6 register) 8-bit data: 11111111B Data byte (8 bits) Start bit (1) (1) (1) (1) (1) (1) Stop bits (2 bits) (1) (1) (1) Transmission pin (TxD6 pin) Reception pin (RxD6 pin) Transmission completion interrupt (INTST6 signal) For details about the DALI interface control by using 78K0/Ix2 microcontroller, see the following document. • Controlling Fluorescent Lamp Ballasts by Using 78K0/Ix2 Application Note (Document No.: U19665) 26 Application Note U19666EJ1V0AN APPENDIX A REFERENCE CIRCUIT DIAGRAM (EZ-0005) Caution Note that the evaluation board and its schematic are designed for evaluating high brightness control using the 78K0/Ix2 microcontroller and are not intended for use in the final product. Application Note U19666EJ1V0AN 27 APPENDIX A REFERENCE CIRCUIT DIAGRAM (EZ-0005) 28 Application Note U19666EJ1V0AN APPENDIX B REFERENCE PARTS TABLE (EZ-0005) Table B-1. Reference Parts Table (EX-0005) (1/2) Item No. C101 C103 C104 C110 C111 C201 C203 C204 C210 C211 C212 C213 C301 C303 C304 C401 C508 C510 C601 CN4 CN7 CN8 CN9 D101 D102 D103 D104 D201 D202 D203 D204 D301 D302 D303 D304 D601 D602 L101 L201 L301 Q101 Q102 Q103 Q201 Q202 Q203 Q301 Q302 Q303 Maker MURATA TAIYO YUDEN MURATA MURATA TAIYO YUDEN MURATA TAIYO YUDEN MURATA MURATA TAIYO YUDEN MURATA TAIYO YUDEN MURATA TAIYO YUDEN MURATA MURATA MURATA MURATA TAIYO YUDEN HONDA SATO_Parts SATO_Parts SwitchCraft NICHIA ROHM NEC Electronics ROHM NICHIA ROHM NEC Electronics ROHM NICHIA ROHM NEC Electronics ROHM ROHM NEC Electronics TDK TDK TDK NEC Electronics ROHM NEC Electronics NEC Electronics ROHM NEC Electronics NEC Electronics ROHM NEC Electronics Part No. GRM31CR60J107M UMK325BJ106KH-J GRM188B11H102KA01D GRM188B31H104KA92D UMK325BJ106KH-J GRM31CR60J107M UMK325BJ106KH-J GRM188B11H102KA01D GRM188B31H104KA92D UMK325BJ106KH-J GRM188B31H104KA92D UMK325BJ106KH-J GRM31CR60J107M UMK325BJ106KH-J GRM188B11H102KA01D GRM188B31H104KA92D GRM188B31E105K GRM188B31E105K UMK325BJ106KH-J FFC-20BMEP1 ML-800S1V-3P ML-800S1V-2P RAPC722 NS6R083 RB055LA-40 RD4.3FM RB055LA-40 NS6G083 RB055LA-40 RD4.3FM RB055LA-40 NS6B083 RB055LA-40 RD4.3FM RB055LA-40 RB055LA-40 RD4.3FM SLF7045T-151MR40-PF SLF7045T-151MR40-PF SLF7045T-151MR40-PF μPA679TB DTC123JM 2SJ355 μPA679TB DTC123JM 2SJ355 μPA679TB DTC123JM 2SJ355 Application Note U19666EJ1V0AN Spec 100 μF/10 V 10 μF /50 V 1000 pF/50 V 0.1 μF/50 V 10 μF/50 V 100 μF/10 V 10 μF/50 V 1000 pF/50 V 0.1 μF/50 V 10 μF/50 V 0.1 μF/50 V 10 μF/50 V 100 μF/10 V 10 μF/50 V 1000 pF/50 V 0.1 μF/50 V 1 μF/25 V 1 μF/25 V 10 μF/50 V MUSEN_YOU ML-800S1V X3 ML-800S1V X2 RAPC722X LED_RED RB055L-40 RD4.3FM RB055L-40 LED_GREEN RB055L-40 RD4.3FM RB055L-40 LED_BLUE RB055L-40 RD4.3FM RB055L-40 RB055L-40 RD4.3FM 150 μH/400 mA 150 μH/400 mA 150 μH/400 mA μPA679TB DTC123JM 2SJ355-AZ μPA679TB DTC123JM 2SJ355-AZ μPA679TB DTC123JM 2SJ355-AZ 29 APPENDIX B REFERENCE PARTS TABLE (EZ-0005) Table B-1. Reference Parts Table (EX-0005) (2/2) Item No. Q601 Q602 Q603 Q604 Q605 R103 R104 R105 R106 R107 R108 R109 R110 R203 R204 R205 R206 R207 R208 R209 R210 R303 R304 R305 R306 R307 R308 R309 R310 R505 R513 R514 R520 R601 R602 R603 R604 R606 R607 R609 R611 R612 R613 R614 R615 R616 SW401 SW501 SW502 U401 VR601 VR602 VR603 30 Maker NEC Electronics NEC Electronics Philipps VISHAY TI KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA KOA COPAL COPAL COPAL NEC Electronics ALPS ALPS ALPS Part No. PS2561AL-1 PS2561AL-1 BC817-25 MB2S SN75176BD RK73B1JTTD202J RK73B2ATTD151J RK73B1JTTD103J RK73B2ATTD151J RK73B1JTTD333J RK73BW3ATTD4R7J SR732ETTDR33F RK73B1JTTD470J RK73B1JTTD202J RK73B2ATTD151J RK73B1JTTD103J RK73B2ATTD151J RK73B1JTTD333J RK73BW3ATTD4R7J SR732ETTDR33F RK73B1JTTD470J RK73B1JTTD202J RK73B2ATTD151J RK73B1JTTD103J RK73B2ATTD151J RK73B1JTTD333J RK73BW3ATTD4R7J SR732ETTDR33F RK73B1JTTD470J RK73B1ETTD103J RK73B1ETTD104J RK73B1ETTD104J RK73B1ETTD102J RK73B1ETTD103J RK73H1JTTD1211F RK73H1JTTD3320F RK73H1JTTD3161F RK73B2ATTD113J RK73BW3ATTD4R7J RK73B1ETTD121J RK73B1ETTD103J RK73B1ETTD102J RK73B1ETTD152J RK73B1ETTD222J RK73B1ETTD472J RK73B1ETTD102J CAS-220TB1 B3S-1000 CVS-08B μPD78F0756 RS15111A900B RS15111A900B RS15111A900B Application Note U19666EJ1V0AN Spec PS2561AL-1 PS2561AL-1 BC817-25 MB2S SN75176BD 2k 150,1/4 W 10 k 150,1/4 W 33 k 4.7/1 W 0.33/0.25 W 47 2k 150,1/4 W 10 k 150,1/4 W 33 k 4.7/1 W 0.33/0.25 W 47 2k 150,1/4 W 10 k 150,1/4 W 33 k 4.7/1 W 0.33/0.25 W 47 10 k 100 k 100 k 1k 10 k 1.21 k 332 3.16 k 11 k 4.7/1 W 120 10 k 1k 1.5 k 2.2 k 4.7 k 1k CAS-220TB1 B3S-1000 CVS-08B μPD78F0756 RS15111A900B RS15111A900B RS15111A900B APPENDIX C EXAMPLE INTERNAL REFERENCE VOLTAGES AND PWM OUTPUT DUTY PARAMETERS (FOR INTERNAL COMPARATOR FEEDBACK) Table C-1. Example Internal Reference Voltages and PWM Output Duty Parameters (For Internal Comparator Feedback) ILED required(mA) Vref required 300 287 277 266 255 245 234 223 213 202 191 181 170 160 149 138 128 117 106 96 85 74 64 53 43 32 21 11 1.4 1.35 1.3 1.25 1.2 1.15 1.1 1.05 1 0.95 0.9 0.85 0.8 0.75 0.7 0.65 0.6 0.55 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 Caution Channel 1(GREEN) Channel 2(BLUE) Channel 0(RED) DUTY_max0[28] DUTY_min0[28] DUTY_max1[28] DUTY_min1[28] DUTY_max2[28] DUTY_min2[28] TX0CR1 value for TX0CR1 value for TX0CR2 value for TX0CR2 value for TX1CR1 value for TX1CR1 value for CH0(RED) CH0(RED) CH1(GREEN) CH1(GREEN) CH2(BLUE) CH2(BLUE) 129 121 2 80 188 170 125 117 68 85 176 167 123 115 72 89 172 163 119 111 78 91 168 160 115 107 80 95 164 156 113 105 84 99 162 153 109 101 88 102 156 148 105 97 90 106 152 144 101 95 96 110 148 140 97 90 104 115 146 136 95 86 108 119 140 133 91 85 112 123 135 128 87 81 116 128 132 124 83 77 118 132 128 122 79 73 122 138 124 118 77 70 130 143 120 114 73 67 132 147 116 110 71 63 138 152 112 106 67 60 142 157 108 100 65 57 146 161 104 96 63 55 154 167 100 92 61 51 158 174 98 89 57 48 164 178 92 83 55 45 168 182 88 80 53 35 174 196 82 74 47 31 180 202 76 68 35 7 190 238 66 36 23 1 216 250 40 6 The above parameters are not guaranteed because they were calculated using experimented results. Application Note U19666EJ1V0AN 31 APPENDIX D EXAMPLE A/D CONVERTER EXPECTED VALUES AND PWM OUTPUT DUTY PARAMETERS (FOR INTERNAL A/D CONVERTER FEEDBACK) Table D-1. Example A/D Converter Expected Values and PWM Output Duty Parameters (For Internal A/D Converter Feedback) ILED required(mA) Vref required Adref[28] Target ADC value 300 287 277 266 255 245 234 223 213 202 191 181 170 160 149 138 128 117 106 96 85 74 64 53 43 32 21 11 1.4 1.35 1.3 1.25 1.2 1.15 1.1 1.05 1 0.95 0.9 0.85 0.8 0.75 0.7 0.65 0.6 0.55 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 287 276 266 256 246 236 225 215 205 195 184 174 164 154 143 133 123 113 102 92 82 72 61 51 41 31 20 10 Caution DUTYref0[28] TX0CR1 value for CH0(RED) 123 119 116 112 109 106 100 98 94 91 87 84 80 78 74 71 68 64 61 59 56 53 49 46 43 40 22 10 DUTYref2[28] TX1CR1 value for CH2(BLUE) 171 168 164 161 157 154 149 145 141 138 134 130 126 123 119 115 111 107 101 98 94 90 85 81 76 71 39 17 The above parameters are not guaranteed because they were calculated using experimented results. 32 DUTYref1[28] TX0CR2 value for CH1(GREEN) 1 84 88 90 94 98 101 105 109 114 118 122 127 131 137 142 146 151 156 160 166 170 176 181 186 192 224 245 Application Note U19666EJ1V0AN For further information, please contact: NEC Electronics Corporation 1753, Shimonumabe, Nakahara-ku, Kawasaki, Kanagawa 211-8668, Japan Tel: 044-435-5111 http://www.necel.com/ [America] [Europe] [Asia & Oceania] NEC Electronics America, Inc. 2880 Scott Blvd. Santa Clara, CA 95050-2554, U.S.A. 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