TDA1085CG Datasheet TDA1085C, TDA1085CG | P4-P6

TDA1085C

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GENERAL DESCRIPTION

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 failure.

INPUT/OUTPUT FUNCTIONS

(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 smothering

capacitor, the voltage of which is checked by the IC.

When V

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:

•To let 1.0 mA flow through Pin 10 when AC line is

minimum and V

consumption is maximum (fast

ramps and pulses present).

•To let V

reach 3.0 V when AC line provides

maximum current and V

consumption is minimum

(no ramps and no pulses).

•All along the main line cycle, the Pin 10 dynamic range

must not be 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 V

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 inexpensive tachogenerator

which doesn′t need any tuning. During every positive cycle at

Pin 12, the capacitor C

is charged to almost V

and

during this time, Pin 4 delivers a current which is 10 times the

one charging C

. The current source gain is called G and

is tightly specified, but nevertheless requires an adjustment on

. The current into this resistor is proportional to C

and to the motor speed; being filtered by a capacitor, V

becomes smothered and represents the “true actual motor

speed”.

To maintain linearity into the high speed range, it is important

to verify that C

is fully charged: the internal source on Pin

11 has 100KW impedance. Nevertheless C

Pin 11

has to be as

high as possible as it has a large influence on FV/C temperature

factor. A 470 KW resistor 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 circuit.

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 C

up to the moment V

Pin5

(set speed) equals V

(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 5.0mA under Pin 6 full control, as shown by

following conditions:

•Presence of high acceleration ramp V

> V

•Distribution occurs in the V

range (true motor

speed) defined by V

x V

x 2.0 V

For two fixed values of V

and V

, the motor speed

will have high acceleration, excluding the time for V

go from V

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 V

= 0, only the high

acceleration ramp occurs.

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.

TDA1085C

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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 V

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 mA and a specified

transconductance (340 mA/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

Figure 4.

This network must be adjusted experimentally.

In case of a periodic torque variations, Pin 16 directly

provides the phase angle oscillations.

Trigger Pulse Generator (Pins 1, 2, 5, 13, 14, 15)

This circuit performs four functions:

•The conversion of the control amplifier DC output

level to a proportional firing angle at every main line

half cycle.

•The calibration of pulse duration.

•The repetition of the pulse if the triac fails to latch on if

the current has been interrupted by brush bounce.

•The delay of firing pulse until the current crosses zero

at wide firing angles and inductive loads.

programs the Pin 14 discharging current. Saw

tooth signal is then fully determined by R15 and C14

(usually 47 nF). Firing pulse duration and repetition period

are in inverse ratio to the saw tooth slope.

Pin 13 is the pulse output and an external limiting resistor

is mandatory. Maximum current capability is 200 mA.

Current Limiter (Pin 3)

Safe operation of the motor and triac under all conditions

is ensured by limiting the peak current. The motor current

develops an alternative voltage in the shunt resistor (0.05 W

in Figure 4). The negative half waves are transferred to Pin

3 which is positively preset at a voltage determined by

resistors R3 and R4. As motor current increases, the

dynamical voltage range of Pin 3 increases and when Pin 3

becomes slightly negative in respect to Pin8, a current

starts to circulate in it. This current, amplified typically 180

times, is then used to discharge Pin 7 capacitor and, as a

result, reduces firing angle down to a value where an

equilibrium is reached. The choice of resistors R3, R4 and

shunt determines the magnitude of the discharge current

signals on C

Pin7

Notice that the current limiter acts only on peak triac

current.

APPLICATION NOTES

(Refer to Figure 4)

Printed Circuit Layout Rules

In the common applications, where TDA 1085C is used,

there is on the same board, presence of high voltage, high

currents as well as low voltage signals where millivolts

count. It is of first magnitude importance to separate them

from each other and to respect the following rules:

•Capacitor decoupling pins, which are the inputs of the

same comparator, must be physically close to the IC,

close to each other and grounded in the same point.

•Ground connection for tachogenerator must be directly

connected to Pin 8 and should ground only the tacho. In

effect, the latter is a first magnitude noise generator due

to its proximity to the motor which induces high dφ/dt

signals.

•The ground pattern must be in the “star style” in order

to fully eliminate power currents flowing in the ground

network devoted to capacitors decoupling sensitive

Pins: 4, 5, 7, 11, 12, 14, 16.

As an example, Figure 5 presents a PC board pattern

which concerns the group of sensitive Pins and their

associated capacitors into which the a.m. rules have been

implemented. Notice the full separation of “Signal World”

from “Power”, one by line AB and their communication by

a unique strip.

These rules will lead to much satisfactory volume

production in the sense that speed adjustment will stay

valid in the entire speed range.

Power Supply

As dropping resistor dissipates noticeable power, it is

necessary to reduce the I

needs down to a minimum.

Triggering pulses, if a certain number of repetitions are kept

in reserve to cope with motor brush wearing at the end of its

life, are the largest I

user. Classical worst case

configuration has to be considered to select dropping

resistor. In addition, the parallel regulator must be always

into its dynamic range, i.e., I

over 1.0 mA and V

over 3.0 V in any extreme configuration. The double

filtering cell is mandatory.

TDA1085C

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Tachogenerator Circuit

The tacho signal voltage is proportional to the motor speed.

Stability considerations, in addition, require an RC filter, the

pole of which must be looked at. The combination of both

elements yield a constant amplitude signal on Pin 12 in most

of the speed range. It is recommended to verify this maximum

amplitude to be within 1.0 V peak in order to have the largest

signal/noise ratio without resetting the integrated circuit

(which occurs if V

reaches 5.5 V). It must be also verified

that the Pin 12 signal is approximately balanced between

“high” (over 300 mV) and “low”. An 8-poles tacho is a

minimum for low speed stability and a 16-poles is even better.

The RC pole of the tacho circuit should be chosen within

30 Hz in order to be as far as possible from the 150 Hz which

corresponds to the AC line 3rd harmonic generated by the

motor during starting procedure. In addition, a high value

resistor coming from V

introduces a positive offset at Pin

12, removes noise to be interpreted as a tacho signal. This

offset should be designed in order to let Pin 12 reach at least

- 200 mV (negative voltage) at the lowest motor speed. We

remember the necessity of an individual tacho ground

connection.

Frequency to Voltage Converter - F V/C

11 has a recommended value of 820 pF for 8-poles

tachos and maximum motor rpm of 15000, and R

11 must

be always 470 K.

Pin4

should be chosen to deliver within 12 V at

maximum motor speed in order to maximize signal/noise

ratio. As the FV/C ratio as well as the C

Pin11

value are

dispersed, R

Pin4

must be adjustable and should be made of

a fixed resistor in service with a trimmer representing 25%

of the total. Adjustment would become easier.

Once adjusted, for instance at maximum motor speed, the

FV/C presents a residual non linearity; the conversion factor

(mV per RPM) increases by within 7.7% as speed draws to

zero. The guaranteed dispersion of the latter being very

narrow, a maximum 1% speed error is guaranteed if during

Pin 5 network design the small set values are modified, once

forever, according this increase.

The following formulas give V





+ G.0 @ (V

–V

) @ C



@ R

@ f @

(1 )

120k

Pin11

)

In volts

G.0

- V

) ] 140

= 2.0 V

120 k = R

int

, on Pin 11

Speed Set (Pin 5)

Upon designer choice, a set of external resistors apply a

series of various voltages corresponding to the various

motor speeds. When switching external resistors, verify that

no voltage below 80 mV is ever applied to Pin 5. If so, a full

circuit reset will occur.

Ramps Generator (Pin 6)

If only a high acceleration ramp is needed, connect Pin 6

to ground.

When a Distribute ramp should occur, preset a voltage on

Pin 6 which corresponds to the motor speed starting ramp

point. Distribution (or low ramp) will continue up to the

moment the motor speed would have reached twice the

starting value.

The ratio of two is imposed by the IC. Nevertheless, it

could be externally changed downwards (Figure 6) or

upwards (Figure 7).

The distribution ramp can be shortened by an external

resistor from V

charging C

, adding its current to the

internal 5.0 mA generator.

Power Circuits

Triac Triggering pulse amplitude must be determined by

Pin13 resistor according to the needs in Quadrant IV.

Trigger pulse duration can be disturbed by noise signals

generated by the triac itself, which interfere within Pins 14

and 16, precisely those which determine it. While easily

visible, this effect is harmless.

The triac must be protected from high AC line dV/dt during

external disturbances by 100 nF x 100 W network.

Shunt resistor must be as non-inductive as possible. It can

be made locally by using constantan alloy wire.

When the load is a DC fed universal motor through a

rectifier bridge, the triac must be protected from commutating

dV/dt by a 1.0 to 2.0mH coil in series with MT

Synchronization functions are performed by resistors

sensing AC line and triac conduction. 820 k values are

normal but could be reduced down to 330 k in order to detect

the “zeros” with accuracy and to reduce the residual DC line

component below 20 mA.

Current Limitation

The current limiter starts to discharge Pin 7 capacitor

(reference speed) as the motor current reaches the designed

threshold level. The loop gain is determined by the resistor

connecting Pin 3 to the series shunt. Experience has shown

that its optimal value for a 10Arms limitation is within

2.0 kW. Pin 3 input has a sensitivity in current which is

limited to reasonable values and should not react to spikes.

If not used, Pin 3 must be connected to a maximum

positive voltage of 5.0V rather than be left open.

Loop Stability

The Pin 16 network is predominant and must be adjusted

experimentally during module development. The values

indicated in Figure 4 are typical for washing machine

applications but accept large modifications from one model

to another. R16 (the sole restriction) should not go below

33 k, otherwise slew rate limitation will cause large transient

errors for load steps.

P1-P3 P4-P6 P7-P9 P10-P12

TDA1085CG

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Motor / Motion / Ignition Controllers & Drivers Universal Motor Speed Controller

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