TDA1085C

5

MOTOROLA ANALOG IC DEVICE DATA

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

This circuit performs four functions:

proportional firing angle at every main line half cycle.

has been interrupted by brush bounce.

angles and inductive loads.

RPin 15 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

Ω

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 CPin 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:

comparator, must be physically close to the IC, close to each other

and grounded in the same point.

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 d

φ/dt signals.

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 ICC 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 ICC 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., IPin 10 over 1.0 mA and VPin 10 over 3.0 V in any

extreme configuration. The double filtering cell is mandatory.

Tachogenerator Circuit

The tacho signal voltage is proportional to the motor speed. Stablility

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 VPin 12 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 VCC

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

CPin 11 has a recommended value of 820 pF for 8–poles tachos and

maximum motor rpm of 15000, and RPin 11 must be always 470 K.

RPin 4 should be choosen 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 CPin 11 value are dispersed, RPin 4must be adjustable and

should be made of a fixed resistor in serice 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 VPin 4:

V

Pin 4 +

G.0

@ (V

CC

–Va) @ CPin 11 @ R4 @ f @

(1

) 120k

R

1

In volts.

G.0 . (VCC – Va) ' 140

Va = 2.0 VBE

120 k = Rint, 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.