MLX90323 Datasheet, PDF (12/25 Pages) Melexis Microelectronic Systems – 4 – 20 mA Loop Sensor Interface with Signal Conditioning and EEPROM

MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
Clock Temperature Stabilization
To provide a stable clock frequency from the internal clock over the entire operating temperature range, three
separate clock adjust values are used. Shifts in operating frequency over temperature do not effect the
performance but do, however, cause the communications baud rate to change.
The firmware monitors the internal temperature sensor to determine which of three temperature ranges the
device currently is in. Each temperature range has a factory set clock adjust value, ClkTC1, ClkTC2, and
ClkTC3. The temperature ranges are also factory set. The Ctemp1 and Ctemp2 values differentiate the three
ranges. In order for the temperature A to D value to be scaled consistently with what was used during factory
programming, the CLKgntp (temperature amplifier gain) valued is stored. The Cadj value stored in byte 1 of
the EEPROM is used to control the internal clock frequency while the chip boots.
Unused Bytes
There are eight unused bytes in the EEPROM address map. These bytes can be used by the user to store
information such as a serial number, assembly date code, production line, etc. Melexis doesn’t guarantee that
these bytes will be available to the user in future revisions of the firmware.
EEPROM Checksum
A checksum test is used to ensure the contents of the EEPROM. The eight bit sum of all of the EEPROM
addresses should have a remainder of 0FFh when the checksum test is enabled (mode byte). Byte 47 is
used to make the sum remainder totals 0FFh. If the checksum test fails, the output will be driven to a user
defined value, Faultval. When the checksum test is enabled, the checksum is verified at initialization of RAM
after a reset.
RAM Data
All the coefficients are compacted in a manner similar to that used for the EEPROM. They are stored on 12
bits (instead of keeping 16 bits for each coefficient). All the measurements are stored on 16 bits. The user
must have access to the RAM and the EEPROM, while interrupt reading of the serial port. Therefore, bytes
must be kept available for the return address, the A-accu and the B-accu, when an interrupt occurs. The RAM
keeps the same structure in the both modes.
Table 4. Examples of Fixed Point Signed Numbers
Decimal Hexadecimal
Value
Equivalent
Fixed Point Signed
Number Equivalent
0
1023
1024
2047
2048
3071
3072
0000h
3FFh
400h
7FFh
800h
0BFFh
0C00h
+0.00
+0.9990234
+1.000
+1.9990234
-0.000
-0.9990234
-1.000
4095
0FFFh
-1.9990234
Data Range
Various data are arranged as follows:
Temperature points: 10 bits, 0-03FF in
high-low order.
GN1: 10 bits, 0-03FF in high-low order.
OF1: 10 bits, 0-03FF in high-low order.
GNTCi: signed 12 bits (with MSB for the
sign), [-1.9990234, +1.9990234].
OFTCi: signed 12 bits (with MSB for the
sign), [-1.9990234, +1.9990234].
3901090323
Rev 003
Page 12 of 25
Data Sheet
Feb/12