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AN1320 APPLICATION NOTE

This is an added value of the micro.

An important feature of the overall application is its modularity: we can have a board with the micro and a board

without it changing very few parts, we can also put all the parts on the same PCB and then decide which con-

nection to do.

7.0 COMMENTS:

The lamp disconnection fault is managed as an interrupt not only for fast acting, but also for the characteristics

of the application we have chosen. The ST62E62C has just a PWM output, while the application needs two

PWM. We have solved the problem using the software PWM. This is something very “heavy” for the micro to

perform, and it influences all the other choices: e.g. a polling sequence is to expensive as time consuming and

it influences the SW PWM duty cycle dynamic. It consumes ~25%-30% of the cycle, and this, added to 20% due

to the 4 instructions to do the PWM itself was too large. That is the main reason why the disconnection fault is

managed as an interrupt.

Of course there are different solutions. A feasible choice could be to use the hardware PWM to set the reference

of the non inverting input and not to use the software PWM. But we should relay on the L6574 preheat and ig-

supervise less items.

A third choice might be to choose a

µC with two PWM output: in this way the application has the same charac-

teristics and the

µC has an easier code to run.

8.0 REFERENCES:

1] L6574 datasheet

2] AN993: electronic ballast with PFC using L6574 and L6561

3] ST62E62C datasheet

9.0 APPENDIX:

1) Flow Chart

2) Vardef.inc

3) Ballast.asm