MOTOROLA ANALOG IC DEVICE DATA
The TDA 1085C triggers a triac accordingly to the speed regulation
requirements. Motor speed is digitally sensed by a tachogenerator
and then converted into an analog voltage.
The speed set is externally fixed and is applied to the internal linear
regulation input after having been submitted to programmable
acceleration ramps. The overall result consists in a full motor speed
range with two acceleration ramps which allow efficient washing
machine control (Distribute function).
Additionally, the TDA 1085C protects the whole system against AC
line stop or variations, overcurrent in the motor and tachogenerator
(Refer to Figures 1 and 8)
Voltage Regulator – (Pins 9 and 10) This is a parallel type regulator
able to sink a large amount of current and offering good
characteristics. Current flow is provided from AC line by external
dropping resistors R1, R2, and rectifier: This half wave current is
used to feed a smoothering capacitor, the voltage of which is
checked by the IC.
When VCC is reached, the excess of current is derived by another
dropping resistor R10 and by Pin 10. These three resistors must be
determined in order:
consumption is maximum (fast ramps and pulses present).
10 reach 3.0 V when AC line provides maximum current and
VCC consumption is minimum (no ramps and no pulses).
exceeded unless loss of regulation.
An AC line supply failure would cause shut down.
The double capacitive filter built with R1 and R2 gives an efficient
VCC smoothing and helps to remove noise from set speeds.
Speed Sensing – (Pins 4, 11, 12) The IC is compatible with an
external analog speed sensing: its output must be applied to Pin 4,
and Pin 12 connected to Pin 8.
In most of the applications it is more convenient to use a digital
speed sensing with an unexpensive tachogenerator which
′t need any tuning. During every positive cycle at Pin 12,
the capacitor CPin 11 is charged to almost VCC and during this
time, Pin 4 delivers a current which is 10 times the one charging
CPin 11. The current source gain is called G and is tightly
specified, but nevertheless requires an adjustment on RPin 4. The
current into this resistor is proportional to CPin 11 and to the motor
speed; being filtered by a capacitor, VPin 4 becomes smothered
and represents the “true actual motor speed”.
To maintain linearity into the high speed range, it is important to verify
that CPin 11 is fully charged: the internal source on Pin 11 has 100 KΩ
impedance. Nevertheless CPin 11 has to be as high as possible as it
has a large influence on FV/C temperature factor. A 470 K
between Pins 11 and 9 reduces leakage currents and temperature
factor as well, down to neglectable effects.
Pin 12 also has a monitoring function: when its voltage is above
5.0 V, the trigger pulses are inhibited and the IC is reset. It also
senses the tachogenerator continuity, and in case of any circuit
aperture, it inhibits pulse, avoiding the motor to run out of control. In
the TDA 1085C, Pin 12 is negatively clamped by an internal diode
which removes the necessity of the external one used in the former
Ramp Generator – (Pins 5, 6, 7) The true Set Speed value taken in
consideration by the regulation is the output of the ramp generator
(Pin 7). With a given value of speed set input (Pin 5), the ramp
generator charges an external capacitor CPin 7 up to the moment
VPin 5 (set speed) equals VPin 4 (true speed), see Figure 2. The IC
has an internal charging current source of 1.2mA and delivers it from
0 to 12 V at Pin 7. It is the high acceleration ramp (5.0 s typical) which
allows rapid motor speed changes without excessive strains on the
mechanics. In addition, the TDA 1085C offers the possibility to break
this high acceleration with the introduction of a low acceleration ramp
(called Distribution) by reducing the Pin 7 source current down to
µA under Pin 6 full control, as shown by following conditions:
• Presence of high acceleration ramp VPin 5 > VPin 4
• Distribution occurs in the VPin 4 range (true motor speed) defined
by VPin 6 x VPin 4 x 2.0 VPin 6
For two fixed values of VPin 5 and VPin 6, the motor speed will have
high acceleration, excluding the time for VPin 4 to go from VPin 6
to two times this value, high acceleration again, up to the moment
the motor has reached the set speed value, at which it will stay,
see Figure 3.
Should a reset happen (whatever the cause would be), the above
mentioned successive ramps will be fully reprocessed from 0 to the
maximum speed. If VPin 6 = 0, only the high acceleration ramp
To get a real zero speed position, Pin 5 has been designed in such a
way that its voltage from 0 to 80 mV is interpreted as a true zero. As
a consequence, when changing the speed set position, the designer
must be sure that any transient zero would not occur: if any, the entire
circuit will be reset.
As the voltages applied by Pins 5 and 6 are derived from the internal
voltage regulator supply and Pin 4 voltage is also derived from the
same source, motor speed (which is determined by the ratios
between above mentioned voltages) is totally independent from VCC
variations and temperature factor.
Control Amplifier – (Pin 16) It amplifies the difference between true
speed (Pin 4) and set speed (Pin 5), through the ramp generator. Its
output available at Pin 16 is a double sense current source with a
maximum capability of
± 100 µA and a specified transconductance
µA/V typical). Pin 16 drives directly the trigger pulse generator,
and must be loaded by an electrical network which compensates the
mechanical characteristics of the motor and its load, in order to
provide stability in any condition and shortest transient response; see
This network must be adjusted experimentally.
In case of a periodic torque variations, Pin 16 directly provides the
phase angle oscillations.