MLX90805S datasheet(5/13 Pages) ETC

5 / 13 page

MLX902xx Name of Sensor

Rev Y.X

22/Aug/98

Page 5

MLX90805

Intelligent Triac Controller

MLX90805 Intelligent Triac Controller

Page 5

Rev 1.2

17/May/00

Digital Features

Debounce of ADC

The result from the potentiometer reading must not

jump from one position to the other, therefore a spe-

cial debouncing is designed. The debounce circuit

compares the current value from the ADC with the

previous one. The new value is accepted only if the

absolute difference between the new and the previ-

ous value is greater then 1 LSB.

Power Settings (ROM table)

The ADC output data is applied after debouncing at

the address bus of the ROM and the corresponding

power settings are available at its data output SETP

[9:0]. The content of the ROM can be defined freely:

it does not need to be linearly or continuous. When

the potentiometer setting is changed from one posi-

tion to the other, the phase angle is moved to the

new position via the soft start procedure, avoiding

abrupt changes.

For programming the different speed settings in the

ROM table, following formula can be used, given ti

(in msec) is the delay from the previous zero cross-

ing to the moment of ignition:

f.e.: for a phase angle of 50%, ti = 5msec for a 50Hz

mains, and thus:

Note:

The value should not be negative: very small values

can not be programmed.

Soft Start

The soft start is initiated after the supply voltage has

been built up. This behavior guarantees a gentle

start-up for the motor and automatically ensures the

optimum run-up time. The motor is fired initially with

a very small

phase angle, i.e. a delay time very

close to half the mains period. The phase angle is

than increasing up to the phase angle defined by the

potentiometer setting. The rate of increase is defined

by the option ATN[4:0]. This option defines the time

to increase the phase angle from minimum to maxi-

mum. If the phase angle, selected by the potentiome-

ter, is not the maximum phase angle then the soft

start run-up time is decreased proportionally.

Firing

The soft start circuit generates a predefined set of

values for the ignition angle IGN. These values are

compared with the value of a down counter, which is

clocked by DCLK = 100kHz (the resolution is 10 us)

and is cleared at beginning of every half period of

mains. When the counter value becomes equal to

IGN the firing circuit produces an ignition pulse

GATE with duration 20us, 40us, 80us or 320us. This

duration can be chosen with option DUTS[1:0]. The

retriggering circuit checks whether the triac is ON, if

not additional firing pulses are generated every 20us

(with respect to the end of the previous firing pulse)

until firing of the triac.

Thermal Protection

An external circuitry supplied by VREF defines the

voltage at pin THP. This voltage is proportional to

Tamb. It is tracked by an internal comparator re-

ferred to VREF/2. The tracking process is sampled.

When the switch is ON (see block diagram), the chip

checks if Tamb is greater than a predefined value. If

yes, the motor is driven to operate at the speed de-

fined at the first ROM address. During the time when

the switch is OFF, the chip checks what kind of mode

is defined by the external elements: 2-wire or 3-wire

potentiometer connection. A reconnection of the ele-

ments used for thermal protection is needed only to

define the active mode of operation.

The temperatures for which thermal protection be-

comes active or not are defined by the external ele-

ments, keeping in mind that comparator is referred

toVREF/2.

In the case when thermal protection is not used, pin

THP should be connected to pin FB, which is con-

nected either to Vss or to Vref, depending on the

mode.

2-wire mode, if V(FB) = VREF

3-wire mode, if V(FB) = VSS

]

[

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Fmains

ROMi

490

]

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ROMi

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