ams Datasheet

Page 9

[v1-01] 2015-Oct-12

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AS-MLV-P2 − Application Information

A constant current source can also be used to read-out the

sensitive layer. In this case the electrical power dissipated in the

sensitive layer must be limited and must not exceed 1mW for

Heater Control

To solve the application the sensor needs a certain temperature,

the operation point. This temperature correlates with the

heater resistance of the sensor module. The heater resistance

and its TCR varies with production and the sensor temperature

should be adjusted by applying a calibration step up front. In

this calibration step the characteristic of the correlation of

temperature and heater power is used. For iAQ applications the

dependency for the operation temperature of ~300°C is 34mW

@ 23°C ± 2°C. The measured heater resistance value with this

applied conditions is the set-point which will be important for

the further operation.

Variation of ambient temperature may have an influence in the

sensor temperature and its heater resistance. The chosen circuit

shall be adjustable and should keep the heater resistance

constant at the desired set-point. This can be solved by a basic

PWM circuit shown in Figure 10.

Figure 10:

Basic PWM Circuit for Heater Control

Basic PWM Circuit for Heater Control: A typically heater driver circuit, R1 is the current limit resistor, R2 is

needed as a bypass resistor