AN1320 Datasheet, PDF (8/20 Pages) STMicroelectronics – IN BALLAST APPLICATIONS

AN1320 APPLICATION NOTE
5.2 SOFTWARE CHOICES
We have already done some software choose choosing the microcontroller. When we chose a microcontroller
with only one PWM output we have already decided to devote a certain amount of microcontroller resources to
build the PWM software (see appendix for software details).
A logic sequence of actions could be:
1) to check that everything is ok - i.e. all the ICs are supplied in the right way;
2) check the presence of the load
3) do the preheat sequence
4) check lamp ignition
5) set the current in the load according to the user input
This is a basic set of functions typical of nearly any ballast application (see fig. 7)
Figure 7. Flow Chart
N
L6574 OK?
Y
Y
open load?
N
ST6 start up
8/20
set Fpre
N
t>Tpre?
Y
set IGN freq.
profile
wait for reset
and/or power
off
L6574 and
L6561 disable
N
lamp on?
N
Y
#fail<MAX?
Y
set working
freq.
(freq.&loop
ref.)
Y
N
dimming?
Y
fault cd.?
N