MLX90805S datasheet(9/13 Pages) ETC

9 / 13 page

MLX902xx Name of Sensor

Rev Y.X

22/Aug/98

Page 9

MLX90805

Intelligent Triac Controller

MLX90805 Intelligent Triac Controller

Page 9

Rev 1.2

17/May/00

Applications Example - Soft Start with 2-Wire Setting

90805

T H P

Vref

SET

NTC

Pot

Vss

Vdda

TRG

Soft Start With 2-Wire Setting

The speed control is performed in addition to the soft

start in this application. A potentiometer in 2-wire

connection is used to define different speed settings.

An additional resistor RP with value equal to the po-

tentiometer is used to keep the ADC input to be ra-

tiometric. In this case, the input signal for the ADC

varies between 0 and VREF/2.

The minimum speed corresponds to a potentiometer

set to its minimum value (i.e. Rpot = 0). Maximum

speed corresponds to a potentiometer set to its maxi-

mum value. When the mains voltage is applied to the

system, the motor starts running at a speed defined

by the potentiometer, as soon as the soft start time

has finished.

The disadvantage of the 2-wire application is that, at

maximum speed setting, the tolerance on the abso-

lute value of the potentiometer defines the tolerance

of the voltage at the SET input, resulting in a less

accurate selection of the maximum speed setting.

This can be avoided when using the 3-wire applica-

tion.

The voltage at SET is transferred to a 4 bit value to

address a ROM table in which the different phase

angles are defined with a 10 bit resolution.

The 2-wire mode is selected by connecting VFB to

VREF (eventually via a resistor).

Note:

R1, R2 and NTC are only needed for thermal pro-

tection, and can be left out otherwise

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