MLX90251
Programmable Linear Hall Effect Sensor
3901090251 Page 17 of 20 Data Sheet
Rev 012 Oct/2012
Note: External capacitors and resistors will effect the rise and fall times for the programming waveforms.
Program pulse timings may require adjustment for the application. The device can not be programmed if
MEMLOCK equals 1.
The EEPROM contents can be read from the device. This procedure, known as a read back, is done by
sending a read command and then measuring the supply current. To successfully read the EEPROM it must
be possible to measure the supply current to the device. The Melexis PTC hardware and software tools
contain built in functions for reading the EEPROM.
The MLX90251 can be programmed by using the PTC-04 programmer and the dedicated software tools. The
timing and voltage levels are controlled through the programming hardware and software. Further details can
be found in the MLX90251 software documentation.
12.3 Calibration Procedure
The programmable features of the device allow for calibration within the application. This section gives
general information for a two point calibration procedure. The two point calibration is the most common
however, it is possible to adapt other procedures.
1.) The first step in the calibration procedure is to initialize the device. This is done by establishing
communication and reading the contents of the EEPROM.
2.)The second step is to set the TempCo and FILTER settings.
3.) Step three is the evaluation of position one. During this step the output voltage is measured with initial
values for RG, FG and OFFSET.
4.) Step four is the evaluation of position two. During this step, the output voltage is measured with the same
values from step 3. From the measurements it is possible to calculate the slope and offset error. Next the
output slope transfer characteristic versus FG and RG is interpolated. With this information the initial settings
are adjusted and the output voltage is measured again.
5.) Step five is the final check and adjustment. At this stage small corrections are made to the OFFSET and
FG parameters. Next, the output clamping parameters, CLAMPHIGH and CLAMPLOW, are determined.
6.) The sixth step is the program phase. Now that all the parameters are determined and the application
requirements are satisfied, the settings are programmed into the EEPROM.
7.) The final step, seven, is the lock and verify step. Here the customer can perform any number of additional
measurements and verify the EEPROM contents. After this is completed the MEMLOCK is set and the
EEPROM is locked, preventing any further programming.
Note: EEPROM verification is done by reading the contents of the EEPROM and comparing it to the data
written. It is possible to read the EEPROM contents regardless of the status of MEMLOCK.
The Melexis PTC software tools contain built in functions and procedures for calibrating the MLX90251.
Please refer to the software documentation for more information on how to use the calibration tools.
The output of the MLX90251 is ratiometric. To avoid calibration errors from fluctuations in the supply voltage,
the output voltage should be measured as a percentage of the supply voltage.
