MLX90621 datasheet(37/44 Pages) MELEXIS

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MLX90621

16x4 IR array

Datasheet

39001090621

Page 37 of 44

Datasheet IR16x4

Rev 3.0

15 September 2016

Applications Information

11.

Use of the MLX90621 thermometer in I

2C configuration

11.1.

Figure 30: MLX90621 I

2C connection

As the MLX90621xxx is fully I

2C compatible it allows to have a system in which the MCU may be supplied with

VDD=2.5…5V while the sensor it’s self is supplied from separate supply VDD1=2.6V (or even left with no supply i.e.

VDD=0V), with the I

2C connection running at supply voltage of the MCU.

Application Comments

12.

Significant contamination at the optical input side (sensor filter) might cause unknown additional filtering/distortion

of the optical signal and therefore result in unspecified errors.

IR sensors are inherently susceptible to errors caused by thermal gradients. There are physical reasons

for these phenomena and, in spite of the careful design of the MLX90621xxx, it is recommended not to

subject the MLX90621 to heat transfer and especially transient conditions.

The MLX90621 is designed and calibrated to operate as a non-contact thermometer in settled conditions.

Using the thermometer in a very different way will result in unknown results.

Capacitive loading on an I

2C can degrade the communication. Some improvement is possible with use of current

sources compared to resistors in pull-up circuitry. Further improvement is possible with specialized commercially

available bus accelerators. With the MLX90621 additional improvement is possible by increasing the pull-up current

(decreasing the pull-up resistor values). Input levels for I

2C compatible mode have higher overall tolerance than the

2C specification, but the output low level is rather low even with the high-power I2C specification for pull-up

currents. Another option might be to go for a slower communication (clock speed), as the MLX90621 implements

Schmidt triggers on its inputs in I

2C compatible mode and is therefore not really sensitive to rise time of the bus (it is

more likely the rise time to be an issue than the fall time, as far as the I

2C systems are open drain with pull-up).

2 - SDA

4 - VSS

3 - VDD

1 - SCL

MCU

VDD

VDD1

MCU VDD = 2.5...5V

SENSOR VDD = 2.6V

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