UAA2016

5

MOTOROLA ANALOG IC DEVICE DATA

CIRCUIT FUNCTIONAL DESCRIPTION

Power Supply (Pin 5 and Pin 7)

The application uses a current source supplied by a single

high voltage rectifier in series with a power dropping resistor.

An integrated shunt regulator delivers a VEE voltage of

– 8.6 V with respect to Pin 7. The current used by the total

regulating system can be shared in four functional blocks: IC

supply, sensing bridge, triac gate firing pulses and zener

current. The integrated zener, as in any shunt regulator,

absorbs the excess supply current. The 50 Hz pulsed supply

current is smoothed by the large value capacitor connected

between Pins 5 and 7.

Temperature Sensing (Pin 3)

The actual temperature is sensed by a negative

temperature coefficient element connected in a resistor

divider fashion. This two element network is connected

between the ground terminal Pin 5 and the reference voltage

– 5.5 V available on Pin 1. The resulting voltage, a function of

the measured temperature, is applied to Pin 3 and internally

compared to a control voltage whose value depends on

several elements: Sawtooth, Temperature Reduction and

Hysteresis Adjust. (Refer to Application Information.)

Temperature Reduction

For energy saving, a remotely programmable temperature

reduction is available on Pin 4. The choice of resistor R1

connected between Pin 4 and VCC sets the temperature

reduction level.

Comparator

When the positive input (Pin 3) receives a voltage greater

than the internal reference value, the comparator allows the

triggering logic to deliver pulses to the triac gate. To improve

the noise immunity, the comparator has an adjustable

hysteresis. The external resistor R3 connected to Pin 2 sets

the hysteresis level. Setting Pin 2 open makes a 10 mV

hysteresis level, corresponding to 0.15

°C. Maximum

hysteresis is obtained by connecting Pin 2 to VCC. In that

case the level is set at 5

°C. This configuration can be useful

for low temperature inertia systems.

Sawtooth Generator

In order to comply with European norms, the ON/OFF

period on the load must exceed 30 seconds. This is achieved

by an internal digital sawtooth which performs the

proportional regulation without any additional component.

The sawtooth signal is added to the reference applied to the

comparator negative input. Figure 2 shows the regulation

improvement using the proportional band action.

Noise Immunity

The noisy environment requires good immunity. Both the

voltage reference and the comparator hysteresis minimize

the noise effect on the comparator input. In addition the

effective triac triggering is enabled every 1/3 sec.

Failsafe

Output pulses are inhibited by the “failsafe” circuit if the

comparator input voltage exceeds the specified threshold

voltage. This would occur if the temperature sensor circuit is

open.

Sampling Full Wave Logic

Two consecutive zero–crossing trigger pulses are

generated at every positive mains half–cycle. This ensures

that the number of delivered pulses is even in every case.

The pulse length is selectable by Rsync connected on Pin 8.

The pulse is centered on the zero–crossing mains waveform.

Pulse Amplifier

The pulse amplifier circuit sinks current pulses from Pin 6

to VEE. The minimum amplitude is 70 mA. The triac is then

triggered in quadrants II and III. The effective output current

amplitude is given by the external resistor Rout. Eventually,

an LED can be inserted in series with the Triac gate (see

Figure 1).

TA = – 20°C

TA = 0°C

140

80

200

Figure 4. Output Resistor versus

Triac Gate Current

IGT, TRIAC GATE CURRENT SPECIFIED AT 25°C (mA)

20

60

160

180

40

50

40

30

60

120

100

Figure 5. Minimum Output Current

versus Output Resistor

TA = – 20°C

TA = + 85°C

200

180

160

140

120

100

80

60

40

100

Rout, OUTPUT RESISTOR (Ω)

0

20

40

60

80

TA = +10°C

TA = –10°C