Another unique feature of the sensor interface is its ability to
enable programmable clamping at low- and high-output levels.
Enabling clamping ensures the sensor’s ability to detect minimum
and maximum output levels and the ability of the ECU to check
whether the sensor’s output is within an acceptable range.
Furthermore, the MLX90320 sensor interface in our example
integrates fault detection, making it suitable for a range of automotive
applications. Capable of detecting internal and external faults,
this allows for the detection of a poor sensing-element connection.
If the chip receives an incorrect input level from the sensor, in
the arenas of lower than 1.5 V or higher than 3.5 V, possibly the
result of a short circuit to ground or to supply, the IC will then
generate an output level outside of the clamping-level range. In
turn, the ECU detects the event.
Also of interest, this particular interface can program the sensor
interface through the actual connector. The module containing
the sensing element and the interface are integrated into one
housing with only the application pins connected to the outside
of the module. It isn’t necessary to add additional communication
lines since the output pin acts as both an analog output pin and as
a communication pin.
Through short-circuit detection, the IC knows that the user
is requesting the pin for communication. To guarantee that no
changes to memory parameters occur via a short circuit, a specific
timing forms the basis of this detection. Furthermore, the interface
chip includes an option to lock the EEPROM to avoid accidentally
changing a calibrated device. In essence, by using the output
of the interface we can communicate with the chip and calibrate
the parameters in EEPROM with user-defined characteristics.
Evaluation boards are available for calibrating the interface.
These boards include all the hardware necessary for communicating
with the interface, accompanying software, and production
software. The production software can control all necessary production
equipment and communicate with the device to quickly
calibrate hundreds of samples.
APPLICATIONS
Sensor interfaces are ubiquitous in cars. They translate sensor signals
into readable language and simultaneously filter out disturbing
external elements to ensure the correct message gets sent.
We find sensors of various types in common rail, suspension,
and transmission systems as well as in HVAC applications, fuel
and gas injection systems, engine control (fuel, oil boost), anti-lock
braking systems, and many other areas of the vehicle. They are so
widely used that people tend to forget them. Understanding their
capabilities will foster the use of these irreplaceable workhorses in
an ever-increasing number of applications.