ST AN1900 APPLICATION NOTE

AN1900

Application note

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

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

		Ballast	Ballast	DALI Slave
				Software
DALI		1-10 V	1-10 V
Master
		DALI	DALI
		Slave	Slave
	DALI	Board	Board
	Master
	Board			Up to 64 slaves
			DALI Evaluation Kit

Please refer to the ST7DALI-EVAL Evaluation Kit user manual.

March 2009

Rev 2

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Contents	AN1900

Contents

1	Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		. . . . . 3
	1.1	ST7DALIF2 features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. . . . . 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 . . . . . . . . . . . . . . . . . . . . . . . . .	. . . . . 4

2	Schematics and PCB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		. 7
	2.1	Schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	7
	2.2	PCB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	9
	2.3	Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	9
3	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		10

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AN1900	Hardware

1 Hardware

1.1ST7DALIF2 features

	Table 1.	List of requirements for the microcontroller
	Minimum requirements		ST7DALIF2 features
	26 bytes of EEPROM, to save non-		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.
	I/Os and PWM outputs to perform the		Up to 15 multi-functional I/Os, one 12-bit Auto-reload
			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.

1.2Interface 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 ST7DALIF2 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 & 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.

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Hardware	AN1900

Figure 3. ST7DALI-EVAL DALI slave evaluation board

1.3Handling 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.

1.4Power consumption considerations

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 standby, 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.

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