MLX90804 Datasheet, PDF (6/12 Pages) List of Unclassifed Manufacturers – Speed regulator for universal motors

MLX90804
Speed regulator for universal motors
Digital features
Ignition detector
This block tracks if the triac is ON after each firing
pulse. It senses the voltage at the gate of the triac. If
the triac is OFF 10us after a firing pulse, a new pulse
will be generated.
There is an option (active mask) allowing to eliminate
the ignition detector circuit. Two firing pulses are
generated every half period to fire the triac, instead.
Debounce of ADC
To assure a stable operation, the result from
potentiometer reading is debounced before passing
through.
Set of speeds (ROM table)
The analog voltage at pin SET is converted to a
digital value. This digital value is addressing a value
in the ROM table. This value defines the required
speed and has a resolution of 10 bits.
The definition of the speed settings is totally free: it
SWITCH
position
1
2
3
4
5
6
POT
settings
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
SPEED
[rpm]
1700
1700
1700
1700
0
0
2000
2000
3500
3500
7200
7200
12200
12200
12200
12200
does not need to be linear, nor continuously, and
different ROM adresses can have the same speed.
An example can be found in the table: this is an
application where the SET input voltage is defined
with a rotating knob which has only 6 positions.
Switch position 1 corresponds to a very low speed
(1700 rpm) and covers position 0 to 3 of the AD
converter. Switch position 2, corresponding to ADC
position 4 and 5 has zero speed. For switch position
3 to 6 the speed setting is increasing.
Multiplier of input frequency from
sensor
A frequency multiplier is designed in order to
guarantee accurate measuring of the low frequency
at the SPD input. The multiplier has measured the
period of Fspd =>N = Tspd*Fm;
where Tspd =1/Fspd;
Fm=Fosc/MULT.
The value N determines the division coefficient of a
down counter (divider), which clock input is Fosc.
The output frequency from this counter has value
Fout = Fosc/N = Fosc/(Tspd*(Fosc/MULT)) =
Fspd*MULT. The output frequency is Fspd multiplied
by coefficient MULT. The coefficient MULT is
programmable from 1 to 256.
Frequency meter
The frequency meter is implemented as a simple
counter .This counter is cleared at the beginning of
every mains period (20ms) .During the mains period
the output frequency from the frequency multiplier
(Fout = Fref*Mult) is applied at the clock input of this
counter. At the end of the mains period the value of
the counter is stored in a latch. This stored value is
proportional to Fspd and equals
Tmains*Fspd*MULT.
The frequency can be measured during a full or
during half a period of the mains.
If option FP = 1 the frequency is measured over a full
mains period.
If option FP = 0 the frequency is measured for a half
mains period.
Soft start
The soft start is initiated after a proper power on
reset sequence. The startup sequence can be
influenced by several options.
The initial phase angle applied to the triac is defined
as (MIN[9:0] - LD[9:0]), where MIN[9:0] is the
minimum allowed firing angle, and LD[9:0] is the
value initially stored in the integrator. The phase
angle remains unchanged for a duration defined by
the startup time SFT[1:0].
After that time the PI regulator is enabled with a Kp
factor defined by PX[3:1]. As long as the measured
speed is smaller then the start speed (defined by
SPE[1:0]), the error signal at the input of the PI
MLX90804 Speed regulator for universal motors
Page 6
Rev 1.0 30/Jun/00