Hardware implementation for ST7DALI-EVAL
Contents
1. SrO AND AJA Applicationnote Hardware implementation for ST7DALI EVAL Introduction This application note describes how to implement a DALI Digital Addressable Lighting Interface in an existing high frequency dimmable tube lamp ballast application Figure 1 Hardware overview with MCU handling only DALI communication ANALOG ANALOG H DC H B Controller Lres Feedback Feedback If necessary please refer to Application Note AN1756 Choosing a DALI implementation Strategy with ST7DALIF2 for further background This application note is issued with the ST7DALI evaluation board which can be purchased with the sales type ST7DALI EVAL Figure 2 ST7DALI EVAL principle NT NLA il l I il I Ballast Ballast DALI Slave Software DALI 110V 110V N Master DALI Slave Board Up to 64 slaves DALI Evaluation Kit Please refer to the ST7DALI EVAL Evaluation Kit user manual March 2009 Rev 2 1 11 www st com Contents AN1900 Contents 1 MOWA PAPA AA AA 3 1 1 ST7DALIF2 features eee 3 1 2 Interface between microcontroller and analog half bridge controller 3 1 3 Handling DALI reception and transmission with DCM peripheral 4 1 4 Power consumption considerations 0 cee eee ee es 4 2 Schematics and PCB saad NN BALA AN dose ee NGA 7 2 1 NMAC AA AA E wees 7 2 2 POD 2itebecteewdtouteadedad tanteuteeeteseigetysegeneteete 9 2 3 Bill Of Malenal ons anes ese wens2. dee seed e eee ee BES eee eos Eee es 9 3 Revision history 2 0 0 e es 10 2 11 AY AN1900 1 1 1 1 2 Hardware Hardware ST7DALIF2 features Table 1 List of requirements for the microcontroller 20 eo Ona nM O SAYO MoN 256 bytes data internal EEPROM volatile parameters 3 Kbytes program memory 8 Kbytes Flash program memory A timer with Input Capture Output Compare capabilities to receive and DALI communication module DCM transmit DALI signals Low consumption mode to save Halt power saving mode energy between commands Up to 15 multi functional I Os one 12 bit Auto reload ue ane Ka Gu puts to periorm tie Timer with 4 PWM outputs input capture and output interface with the ballast controller compare functions A clock source Internal 1 RC oscillator In addition to DALI protocol handling but without fully controlling the ballast the microcontroller can also monitor or customize some ballast parameters for example for easy calibration of various power levels in the factory and or act as a supervisor of the complete ballast parameters Interface between microcontroller and analog half bridge controller A potential hardware problem is the interface between the microcontroller and the analog half bridge controller One possibility is to use PWM outputs and to filter them to create analog setpoints for the half bridge controller The 4 PWM outputs of the Autoreload timer enable ST7DAL
3. 14 ST7FDALIF2M6 ng Sh SFH6156 2 10K When the bus is high steady state 500 pA is always flowing through the resistor Because the microcontroller should always know if the bus is constantly low bus failure an alternative and more power saving topology is not possible On the one hand current in the resistor should be as low as possible but on the other hand it should not be so low that any noise fools the microcontroller When the transistor turns off the current should be high enough to evacuate the carriers within the right time frame 10 kohms is a good trade off please refer to the I O ports section of the ST7DALIF2 data sheet Here is a summary depending on the frequency chosen Table 2 Power consumption overview a Finally the accuracy of the ST7DALIF2 ADC is directly proportional to the Vpp regulation accuracy If the microcontroller supply is regulated with a standard zener diode for example the ADC precision would be around 10 If precise measurements have to be performed then a voltage regulator with low quiescent current and high precision is needed typically from the LD2980 series a AN1900 2 2 1 Schematics and PCB Schematics and PCB Schematics Aside from the ST7DALIF2 microcontroller itself the ST7DALI EVAL DALI Slave board has four main sections Power Supply DALI Bus ST7DALIF2 Interface In Circuit Communication 1 10 V Interface see Figure 7 The power supply section is v
4. IF2 to act on up to 4 different external parameter pins of the half bridge controller for example L6574 without computation load Please refer to AN993 L6574 amp Microcontroller in ballast applications The designer is then in total control of the lamp Another easier solution is to keep the 1 10 V input widely used for dimming level control and use the microcontroller as a gateway or interface between the DALI bus and the analog input of a conventional analog dimmable ballast The microcontroller is then no longer in direct connection with the analog ballast controller Based on this topology a DALI master board based on the ST72F334J4 has been built and a DALI slave board based on the ST7DALIF2 has been developed and can be seen in Figure 3 3 11 Hardware 1 3 1 4 4 11 AN1900 Figure 3 ST7DALI EVAL DALI slave evaluation board ST TFDALIF2NG pap Handling DALI reception and transmission with DCM peripheral The major embedded feature of the ST7DALIF2 microcontroller is the DALI Communication Module DCM It allows decoding of the DALI forward frame and sending of the backward frame without any CPU overhead or need for a timer with Input Capture or Output Compare capabilities It simplifies the software saves processing time and eases interrupt management The DCM drivers can be found in the ST7 Software Library or in the AN1601 Software Implementation for ST7DALI EVAL Power consumption consid
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6. ace A PWM with programmable duty cycle is generated by the ST7DALIF2 filtered to a DC value proportional to the duty cycle and amplified from 0 5 V to 1 10 V through to the operational amplifier U2A Regardless of whether a ballast is available or not the LED LD3 gives an overview of the light level 7 11 AN1900 Schematics and PCB ST7DALI EVAL DALI slave schematic Figure 7 SIEVE ALL WO RESUMU OZ PINZA U a Pl Bg T01 SIEVE eal ly Os tS sna Nga gregal z gt WANT Tena 50 LO ml i 401 al ELA LP ne a z Z BIO pies ALL a l J HI a EY AP Ooms a a Lanina Md bad IHH NO av ATI AY Ba deh Obs T FiO Pa Pa f TASHA PA dP NATO HA TAWA DAS HIE d Eadie S SL AN DAS Hle d Meer ceded 4 4 TE DAWA KATE H d LALN AGS H S Hd OA dH miss a H SONS Hed lasa 5l zgo oo Pa KIT LS O nal SHLD SASH J ALON doe oda dr 10 EO JA LEAL FY a SE a Ange at gg 410 HEE Old 8 11 AN1900 2 2 2 3 Schematics and PCB PCB The PCB has been designed to look like the add on to an existing ballast design see Figure 8 Gerber files are delivered with the ST7DALI EVAL kit Figure 8 EVAL6574 and ST7DALI EVAL evaluation boards together Na y d 74 j a n3 a El we s ela Ree ua L G Bill of material Please refer to the ST7DALI EVAL User Manual 9 11 Revision history AN1900 3 Revision history Table 3 Do
7. cument revision history owe neve g 31 May 2004 Initial release 17 Mar 2009 Changed product references from ST7DALI to ST7DALIF2 a 10 11 AN1900 Please Read Carefully Information in this document is provided solely in connection with ST products STMicroelectronics NV and its subsidiaries ST reserve the right to make changes corrections modifications or improvements to this document and the products and services described herein at any time without notice All ST products are sold pursuant to ST s terms and conditions of sale Purchasers are solely responsible for the choice selection and use of the ST products and services described herein and ST assumes no liability whatsoever relating to the choice selection or use of the ST products and services described herein No license express or implied by estoppel or otherwise to any intellectual property rights is granted under this document If any part of this document refers to any third party products or services it shall not be deemed a license grant by ST for the use of such third party products or services or any intellectual property contained therein or considered as a warranty covering the use in any manner whatsoever of such third party products or services or any intellectual property contained therein UNLESS OTHERWISE SET FORTH IN ST S TERMS AND CONDITIONS OF SALE ST DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY WITH RESPECT TO THE USE AND OR SALE OF S
8. erations One of the biggest issues when designing a DALI ballast is the power supply of the microcontroller when the lamp is off When the lamp is on supplying all devices can be quite easily done via a charge pump taken from the middle point of the half bridge But in stand by the microcontroller should always be powered on and ready to receive a DALI command This energy can only come from the mains The current taken should then be as low as possible to avoid constant dissipation ST7DALIF2 has a power saving mode called halt using the smallest power consumption since everything inside the MCU core peripherals and clock source is frozen After entering this mode only a reset or an external interrupt can wake up the microcontroller The interrupt can be triggered by the first falling edge of the DALI frame When this happens Run mode is not immediately operational mainly because of the stabilization time of the clock source This time has to be short enough to be able to detect the second rising edge of a DALI frame The first falling edge is not significant but helps to wake up from Halt mode Figure 4 shows on channel 1 the DALI frame on the DALI IN pin of the microcontroller a pulse on channel 3 shows the beginning of the run mode and a high level on channel 4 shows that a proper DALI frame has been received and that the data is ready to be handled by the software AN1900 Hardware Figure 4 Overview of a forward f
9. ery simple A LD2980 provides an accurate 5V output while jumper 4 allows you to easily measure the current used by the power supply the microcontroller and the interface with the DALI Bus The bridge diode protects the DALI Bus ST7DALIF2 interface against wrong polarity wiring however it is not protected from over voltage from accidental mains connection between the control wires For such protection a high voltage switch is needed Since the DALI Protocol specifies that isolation is required two optocouplers are needed one for transmission U4 and one for the reception U5 For cost reasons the transmission optocoupler cannot sustain the 250 mA required to pull the DALI bus down it is high in steady state so a power stage has to be implemented via Q1 For the bus to be kept down during transmission capacitor C7 is used since a voltage must remain on the base of Q1 To avoid a discharge of this capacitor via the optocoupler U5 the diode D6 is required Finally the zener diode D5 is used to ensure that the wide voltage specifications of the DALI bus High level 9 5 to 22 5 V Typical 16 V Low level 6 5 to 6 5 V Typical 0 V can be fulfilled The ST7 In Circuit Communication ICC allows In Circuit Programming ICP and In Application Programming IAP Please refer to the Flash program memory section of the ST7DALIF2 datasheet A standard dimmable ballast can be easily driven through the evaluation board with the 1 10 V Interf
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11. rame reception 2 ms 2 00 V DALI forward frame o Wake up from Halt mode interrupt routine Pa a a Ka 2 Mms HALT ma RUN Mode To better understand how the ST7DALIF2 can wake up fast enough a zoom on the first edge is needed as shown in Figure 5 Figure 5 Zoom on the first edges 50 ps 2 00 V HALT Mode RUN Mod m ae rrr 50 ps 2 00 V P56 cpu clock cycle When the first falling edge is detected the microcontroller leaves Halt mode for a transition period of 256 clock cycles At 8 MHz this means around 32 us Since the DCM starts sampling 125 us worst case after the falling edge the microcontroller frequency can be reduced to 4 MHz i e 64 us to wake up from halt Although the software can work at 1 MHz and still comply fully with DALI it is then not possible to use Halt mode for additional power saving at this frequency because the wake up is not fast enough to catch the beginning of the incoming frame When the lamp is off the microcontroller is not the only source of power dissipation The hardware interface between the DALI bus and the microcontroller also takes quite some current as shown in Figure 6 5 11 Hardware 6 11 AN1900 Figure 6 DALI Bus ST7DALIF2 interface MISOAINAPEE MOSVAIN3JPB3 CLKIN AINA PB4 PBS Wake up from Halt DALI IN 4
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