TDA1085C

6

MOTOROLA ANALOG IC DEVICE DATA

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

VCC charging CPin 7, adding its current to the internal 5.0 µA

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

Ω 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 MT2.

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 k

Ω. 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.

Figure 2. Acceleration Ramp

Figure 3. Programmable Double

Acceleration Ramp

V

VPin 5

VPin 7

t

0

VPin 6 = VDS

0

VDS

VDF

High Acceleration

Ramp

Distribution

Low Acceleration

Ramp

High Acceleration

Ramp

VPin 5 fixed set value

Speeds

t

VPin 4

VDF = 2 VDS