MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
Features and Benefits
Application Examples
Programmable Sensor Interface IC with 4 to
20 mA current loop output
Power supply from 6 to 35VDC
External or internal temperature sensor for
compensating temperature errors
Industrial pressure transducers.
Strain gauges, accelerometers, position
sensors, etc.
Any bridge type sensor with current loop
output.
Ordering code
Product Code Temperature Code
MLX90323
K
MLX90323
K
Package Code
DF
DF
Option Code
AAA-000
AAA-000
Legend:
Temperature Code:
Package Code:
Packing Form:
K for Temperature Range -40°C to +125°C
DF for SOIC300Mil
RE for Reel, TU for Tube
Ordering example:
MLX90323KDF-AAA-000-TU
1 Functional Diagram
FET
VDD
VDD1
OFC
Packing Form Code
TU
RE
2 General Description
The IC converts small changes of output voltage
of full Wheatstone resistive bridge (caused by
mechanical stimulus such as pressure, force,
torque, light or magnetic field) to large changes of
the IC output current.
FLT
Supply Regulator
3.5V
DAC_Offset
OPA
0V
2-bit
CSGN
VBP
x 35
x2
VBN
GAIN
0.97V/V
1.24kOhm
INV
Hardware Gain = 70
GAIN
0.48V/V
TMP
Fine Gain DAC
MicroProcessor
ADC
Internal
Temp Sensor
Temp Amp Gain
GNTP [1:0]
IO1
IO2
COMS
3.5V
External
Temp Sensor
GND
CMO
CMN
Coarse Offset
0V
It removes parasitic DC level (Offset) from the
output bridge voltage and amplifies this signal
certain times (Gain). Offset and Gain are
temperature dependant, so the IC allows
temperature compensation of bridge parasitic DC
shift and sensitivity. Temperature can be
measured either by internal or external (resistor)
temperature sensor. The values of Offset and
Gain and their temperature dependency are
gotten during the calibration process and are
stored in the EEPROM..
TSTB
The IC has industry standard 4 – 20 mA current
loop output interface and takes power directly from
2-wire signal line. The MLX90323 works properly
over wide voltage range (from 6 to 35 V) at the
signal line.
3901090323
Rev 003
Page 1 of 25
Data Sheet
Feb/12
MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
Table of Contents
1 Functional Diagram ..........................................................................................................................................1
2 General Description ..........................................................................................................................................1
3 Glossary of Terms ............................................................................................................................................3
4 Absolute Maximum Ratings..............................................................................................................................4
5 Pin Definitions and Descriptions.......................................................................................................................5
6 General Electrical Specifications ......................................................................................................................6
7 Detailed General Description ...........................................................................................................................8
7.1 Understanding 4-20mA current loop interface ...........................................................................................8
7.2 Analog features ..........................................................................................................................................8
7.3 Digital features ...........................................................................................................................................9
7.4 Parameters calculation ............................................................................................................................10
7.5 Communications ......................................................................................................................................11
8 Temperature compensation ...........................................................................................................................13
9 Calibration ......................................................................................................................................................15
9.1 Baseline Calibration .................................................................................................................................15
9.2 Temperature calibration ...........................................................................................................................15
9.3 Calibration procedure ..............................................................................................................................16
10 EEPROM and RAM byte definitions .............................................................................................................17
11 Unique Features ...........................................................................................................................................22
12 Application Information .................................................................................................................................22
13 Standard information regarding manufacturability of Melexis products with different soldering processes 23
14 ESD Precautions ..........................................................................................................................................24
15 Package Information ....................................................................................................................................24
16 Disclaimer .....................................................................................................................................................24
3901090323
Rev 003
Page 2 of 25
Data Sheet
Feb/12
MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
3 Glossary of Terms
CMN
CMO
COMS
CR
CSGN
CSOF
DACFnew
DACFold
DARDIS
EOC
ETMI
ETPI
FET
FG
FLT
GNO
GNOF
GNTP
HS
IFIX
IINV
ILIM
MODSEL
MUX
OFC
PLL
POR
RX
SAR
STC
Tdiff
Text
TMI
TMP
TPI
Tref
TSTB
TX
UART
VBN
VBP
VDD
WCB
WDC
3901090323
Rev 003
Current Mode Negative (supply connection)
Current Output
Communication, Serial
Carriage Return
Coarse Gain
Coarse Offset
Filtered DAC value, new
Filtered DAC value, old
DAC Resistor Disable
End Of Conversion flag bit
Timer Interrupt Enable
Enable Temperature Interrupt
Field Effect Transistor
Fixed Gain
Filter Pin
Gain and Offset adjusted digitized signal
Gain, Offset
Temperature Gain / Offset Coarse adjustment
Hardware / Software limit
fixed current output value
input signal invert command bit
current limit
Mode Select
multiplexer
Offset Control
Phase Locked Loop
Power On Reset
receive
Successive Approximation Register
start A/D conversion
temperature difference
temperature, external
timer Interrupt
temperature signal
temperature interrupt
temperature reference
test mode pin
transmit
Universal Asynchronous Receiver / Transmitter
bridge, positive, input
bridge, negative, input
supply voltage
warn / cold boot
watch dog counter
Page 3 of 25
Data Sheet
Feb/12
MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
4 Absolute Maximum Ratings
Table 1. Absolute Maximum Ratings
Supply voltage VDD Max
6V
Supply voltage VDD Min
4.5V
Supply voltage (operating), VDD1 Max
35V
Supply current, IDD
3.5mA
Reverse voltage protection
-0.7V
Power dissipation, PD
71mW
Operating temperature range, TA
Storage temperature range, TS
Maximum junction temperature, TJ
-40 to +125°
-55 to +150°C
150°C
Exceeding the absolute maximum ratings may cause permanent damage. Exposure to absolute-maximumrated conditions for extended periods may affect device reliability.
3901090323
Rev 003
Page 4 of 25
Data Sheet
Feb/12
MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
5 Pin Definitions and Descriptions
Table 2. Pin Description
Pin
Signal Name
Description
1,2
NC
Do not connect
3
TSTB
Test pin for Melexis production testing. (in normal application connected to
VDD)
4
FLT
Filter pin; allows for connection of a capacitor to the internal analog path.
5
OFC
Offset control output. Provides access to the internal programmed offset
control voltage for use with external circuitry. (unconnected when not used)
6,7
VBN,VBP
Bridge inputs, negative and positive.
8
TMP
Temperature sensor input. An external temperature sensor can be used in
conjunction with the internal one. The external sensor can provide a
temperature reading at the location of the bridge sensor.
9
VDD
Regulated supply voltage. Used for internal analog circuitry to ensure
accurate and stable signal manipulation.
10
FET
Regulator FET gate control. For generating a stable supply for the bridge
sensor and internal analog circuitry (generates regulated voltage for VDD).
11
VDD1
Unregulated supply voltage. Used for digital circuitry and to generate FET
output.
12
NC
Do not connect
13
CMO
Current output.
14
CMN
Current negative rail. Current return path.
15
GND
Power supply return.
16
COMS
Serial communications pin. Bi-directional serial communication signal for
reading and writing to the EEPROM.
3901090323
Rev 003
1
NC
COMS
16
2
NC
GND
15
3
TSTB
CMN
14
4
FLT
CMO
13
5
OFC
NC
12
6
VBN
VDD1
11
7
VBP
FET
10
8
TMP
VDD
9
Page 5 of 25
Data Sheet
Feb/12
MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
6 General Electrical Specifications
Table 3. MLX90323 Electrical Specifications
o
DC operating parameters: TA = -40 to 125 C, VDD1 = 6 to 35VDC (unless otherwise specified).
Parameter
Symbol
Test Conditions
Min
Typ
Max
Units
35
V
Regulator & Consumption
Input voltage range
VIN
VDD1 (Regulator connected)
Supply current
IDD
@ TA = 100ºC
Regulated supply voltage VREG
6
2.1
4.5
Regulated voltage
temperature coefficient
Supply rejection ratio
4.75
mA
5.2
º
-600
PSRR
VDD1 > 6V
V
uV / C
90
dB
Instrumentation Amplifier
Differential input range
VBP-VBN IINV = 0
-2.88
8.38
mV/V(VDD)
Differential input range
VBP-VBN IINV = 1
-8.38
2.88
mV/V(VDD)
38.0
65.0
%VDD
Common mode
input range
Common mode
rejection Ratio
1/2(VBP+VBN)
CMRR
60
Hardware gain
Coarse offset
control Range
Fixed offset control range
dB
69
84
CSOF[1:0] = 00
-4.37
-3.97
CSOF[1:0] = 01
-1.46
-1.09
mV/V
CSOF[1:0] = 10
1.09
1.46
mV/V
CSOF[1:0] = 11
3.97
4.37
mV/V
High
1.71
2.29
mV/V
Low
-2.00
-1.43
mV/V
IA chopper frequency
300
V/V
mV/V
kHz
Gain Stage
Coarse Gain Stage
Coarse Gain
(Fixed Gain = 1023)
3901090323
Rev 003
CSGN = 00
1.05
1.17
V/V
CSGN = 01
1.71
1.89
V/V
CSGN = 10
2.77
3.06
V/V
CSGN = 11
4.48
4.95
V/V
Page 6 of 25
Data Sheet
Feb/12
MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
Fixed gain control range
Table 3. MLX90323 Electrical Specifications (continued)
0.480
0.970
V/V
Output Stage
Fixed gain
RSENSE = 24 ohm
8.4
9.3
mA/V
Output current CMO pin
27
mA
Current sense resistor
24
Ohms
Signal Path ( General)
Overall gain
Current sense res = 24Ω
Overall non-linearity
Bandwidth (-3dB)
39 nF (FLT to GND)
284
2625
mA/V
-0.25
0.25
%
4.2
KHz
2.8
3.5
Temperature Sensor & Amplifier
Temperature sensor sensitivity
390
Temperature sensor output voltage
uV/ºC
70
380
mV
Input voltage range TMP pin
GNTP[1,0] = 00
207
517
mV
@ VDD = 5.0V
GNTP[1,0] = 01
145
367
mV
GNTP[1,0] = 10
101
263
mV
GNTP[1,0] = 11
71
186
mV
DAC / ADC
Resolution
10
Bit
On-Chip RC Oscillator and Clock
Trimmed RC oscillator frequency
86.9
Frequency temperature coefficient
87.8
88.7
kHz
26
Clock Stability with temperature compensation over full
temperature range
Ratio of f (microcontroller main
TURBO = 0
clock and (RC oscillator)
TURBO = 1
-3
Hz/ºC
+3
%
7
28
UART & COMS Pin
UART baud rate
COMS pin input levels
TURBO = 0
2400
Baud
TURBO = 1
9600
Baud
Low
0.3*VDD
V
High
COMS Pin Output Resistance
3901090323
Rev 003
0.7*VDD V
Low
100
Ohms
High
100
kOhms
Page 7 of 25
Data Sheet
Feb/12
MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
7 Detailed General Description
7.1 Understanding 4-20mA current loop interface
MLX90323 IC is optimized for 4 - 20 mA industry standard current loop interface. The 4 - 20mA current loop
shown in Figure 1 is a common method of transmitting sensor information in many industrial applications.
Transmitting sensor information via a current loop is particularly useful when the information has to be sent to
a remote location over long distances. The loop operation is straightforward: a sensor’s output voltage is first
converted to a proportional current, with 4mA normally representing the sensor’s zero-level output, and 20mA
representing the sensor’s full-scale output. Then, a receiver at the remote end converts the 4-20mA current
back into a voltage which in turn can be further processed by a controller module.
Sensor
MLX90323
VB
Signal Line
SLP
Positive
Signal processor / Controller
Transmission Line
E
INP
INM
GND
4 – 20 mA
R
Current loop
power source
Output voltage for
further processing
SLN Signal Line
Negative
Figure 1. Current loop interface diagram
7.2 Analog features
Supply Regulator
A bandgap-stabilized supply-regulator is on-chip while the pass-transistor is external. The bridge-type sensor
is typically powered by the regulated supply (typically 4.75V).
Oscillator
The MLX90323 contains a programmable on-chip RC oscillator. No external components are needed to set
the frequency (87.8 kHz +/-1%). The MCU-clock is generated by a PLL (phase locked loop tuned for 614 kHz
or 2.46 MHz) which locks on the basic oscillator.
The frequency of the internal clock is stabilized over the full temperature range, which is divided into three
regions, each region having a separate digital clock setting. All of the clock frequency programming is done
by Melexis during final test of the component. The device uses the internal temperature sensor to determine
which temperature range setting to use.
Power-On Reset
The Power-On Reset (POR) initializes the state of the digital part after power up. The reset circuitry is
completely internal. The chip is completely reset and fully operational 3.5 ms from the time the supply
crosses 3.5 volts. The POR circuitry will issue another POR if the supply voltage goes below this threshold for
1.0 us.
Temperature Sensor
The temperature measurement, TPO, is generated from the external or internal temperature sensor. This is
converted to a 10-bit number for use in calculating the signal compensation factors. A 2-bit coarse adjustment
GNTP[1:0] is used for the temperature signal gain & offset adjustment.
3901090323
Rev 003
Page 8 of 25
Data Sheet
Feb/12
MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
7.3 Digital features
UART
The serial link is a potentially full-duplex UART. It is receive-buffered, in that it can receive a second byte
before a previously received byte has been read from the receiving register. However, if the first byte is not
read by the time the reception of the second byte is completed, the first byte will be lost. The UART's baud
rate depends on the RC-oscillator's frequency and the "TURBO"-bit (see output port). Transmitted and
received data has the following structure: start bit = 0, 8 bits of data, stop bit = 1.
Sending Data
Writing a byte to port 1 automatically starts a transmission sequence. The TX Interrupt is set when the STOPbit of the byte is latched on the serial line.
Receiving Data
Reception is initialized by a 1 to 0 transition on the serial line (i.e., a START-bit). The baud rate period (i.e.,
the duration of one bit) is divided into 16 phases. The first six and last seven phases of a bit are not used.
The decision on the bit-value is then the result of a majority vote of phase 7, 8 and 9 (i.e., the center of the
bit).
Spike synchronization is avoided by de-bouncing on the incoming data and a verification of the START-bit
value. The RX Interrupt is set when the stop bit is latched in the UART.
Timer
The clock of the timers TMI and TPI is taken directly from the main oscillator. The timers are never reloaded,
so the next interrupt will take place 2x oscillator pulses after the first interrupt.
Watch Dog
An internal watch dog will reset the whole circuit in case of a software crash. If the watch dog counter is not
reset at least once every 26 milliseconds (@ 2.46 MHz main clock), the microcontroller and all the
peripherals will be reset.
Temperature Processing
Temperature reading controls the temperature compensation. This temperature reading is filtered as
designated by the user. The filter adjusts the temperature reading by factoring in a portion of the previous
value. This helps to minimize the effect of noise when using an external temperature sensor. The filter
equation is:
If measured_temp > Temp_f(n) then
Temp_f(n+1) = Temp_f(n) + [measured_temp - Temp_f(n)] / [2 n_factor]
If measured_temp < Temp_f(n), then
n_factor
Temp_f(n+1) = Temp_f(n) - [measured_temp - Temp_f(n)] [2
]
Temp_f(n+1) = new filtered temperature value
Temp_f(n) = previous filtered temperature value
Measured_temp = Value from temperature A to D
n_factor = Filter value set by the user (four LSB’s of byte 25 of EEPROM), range 0-6.
The filtered temperature value, Temp_f, is stored in RAM bytes 58 and 59. The data is a 10 bit value, left
justified in a 16 bit field.
3901090323
Rev 003
Page 9 of 25
Data Sheet
Feb/12
MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
7.4 Parameters calculation
The parameters OF and GN represent, respectively, offset correction and span control, while OFTCi and
GNTCi represent their temperature coefficients (thermal zero shift and thermal span shift). After reset, the
firmware continuously calculates the offset and gain DAC settings as follows: The EEPROM holds
parameters GN, OF, OFTCi and GNTCi, where “i” is the gap number and can be 1 < i < 4. The transfer
function is described below.
GAIN
Iout = FG * DAC_GAIN * CSGN[1:0] * {Vin+DAC_OFFSET+CSOF} * 8.85mA/V
FG = Hardware Gain (~72V/V). Part of the hardware design, and not changeable
CSGN = Course Gain, part of byte 2 in EEPROM.
CSOF = Coarse Offset, part of byte 2 in EEPROM.
DAC_GAIN (new value) ~ GN[9:0] + [GNTCi * dT]
GN[9:0] = Fixed Gain, bytes 3 and 17 in EEPROM.
GNTCi = Gain TC for a given temperature segment I. GNTCiL and GNTCiH in EEPROM table.
dT = Temp. change within the appropriate gap
How to calculate gain in the first temp. gap?:
DAC_GAIN = GN[9:0] - GNTC1 * (T1 – Temp_f1)
How to calculate gain in the other temp. gaps?:
2nd gap: DAC_GAIN = GN[9:0] + GNTC2 * (Temp_f2 – T1)
3rd gap: DAC_GAIN = DAC_GAIN2 + GNTC3 * (Temp_f3 – T2)
4th gap: DAC_GAIN = DAC_GAIN3 + GNTC4 * (Temp_f4 – T3)
Where:
Temp_f = Filtered temp (previously described)
If GNTC1 > 2047 => DAC_GAIN
If GNTC2,3,4 > 2047 => DAC_GAIN ↓
[V/V]
(0.97 − 0.48) *
GN [9 : 0]
+ 0.48 = DAC _ GAIN
1023
OFFSET
DAC_OFFSET (new value) ~ OF[9:0]+[OFTCi* dT]
OF[9:0] = Fixed Gain, bytes 4 and 17 in EEPROM.
OFTCi = Offset for a given temperature segment I. OFTCiL and OFTCiH in EEPROM table.
dT = Temp. change within the appropriate gap.
Calculation of the offset for a given temperature segment is performed the same way as for the gain.
(1.83 − −1.57 ) *
3901090323
Rev 003
OF [9 : 0]
− 1.57 = DAC _ OFFSET [mV/V]
1023
Page 10 of 25
Data Sheet
Feb/12
MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
7.5 Communications
The MLX90323 firmware transfers a complete byte of data into and from the memory based on a simple
command structure. The commands allow data to be read and written to and from the EEPROM and read
from the RAM. RAM data that can be read includes the current digitized temperature. The commands are
described below. Melexis provides setup software for programming the MLX90323.
UART Commands
The commands can be divided into three parts: (1) downloading of data from the ASIC, (2) uploading of data
to the ASIC and (3) the reset command. UART configuration: start bit, 8 data bits, stop bit.
All the commands have the same identification bits. The two MSB’s of the sent byte indicate the command
while the last six MSB’s designate the desired address. The commands are coded as followed:
Command
Read RAM
Write RAM
Read EEPROM
Write EEPROM
Reset
Start
bit
0
0
0
0
0
Bit7
1
0
1
0
1
Bit6
1
0
0
1
0
Bit5
AD5
AD5
AD5
AD5
1
Bit4
AD4
AD4
AD4
AD4
1
Bit3
AD3
AD3
AD3
AD3
1
Bit2
AD2
AD2
AD2
AD2
1
Bit1
AD1
AD1
AD1
AD1
1
Bit0
AD0
AD0
AD0
AD0
1
Stop
Bit
1
1
1
1
1
The addresses can include 0-63 for the RAM, 0-47 for the EEPROM, and 63 for the EEPROM, RESET
Command (read).
Downloading Command
With one byte, data can be downloaded from the ASIC. The ASIC will automatically send the value of the
desired byte.
Uploading Command
Writing to the RAM or EEPROM involves a simple handshaking protocol in which each byte transmitted is
acknowledged by the firmware. The first byte transmitted to the firmware includes both command and
address. The firmware acknowledges receipt of the command and address byte by echoing the same
information back to the transmitter. This “echo” also indicates that the firmware is ready to receive the byte of
data to be stored in RAM or EEPROM. Next, the byte of value to be stored is transmitted and, if successfully
received and stored by the firmware, is acknowledged by a “data received signal,” which is two bytes of value
BCh. If the “data received signal” is not observed, it may be assumed that no value has been stored in RAM
or EEPROM.
Reset Command
Reading the address 63 of the EEPROM resets the ASIC and generates a received receipt indication.
Immediately before reset, the ASIC sends a value of BCh to the UART, indicating that the reset has been
received.
EEPROM Data
All user-settable variables are stored in the EEPROM within the MLX90323. The EEPROM is always reprogrammable. Changes to data in the EEPROM do not take effect until the device is reset via a soft reset or
power cycle. 12 bit variables are stored on 1.5 bytes. The 4 MSB’s are stored in a separate byte and shared
with the four MSB’s of another 12-bit variable.
3901090323
Rev 003
Page 11 of 25
Data Sheet
Feb/12
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
4095
Decimal
Value
Hexadecimal
Equivalent
Fixed Point Signed
Number Equivalent
0
0000h
+0.00
1023
3FFh
+0.9990234
1024
400h
+1.000
2047
7FFh
+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].
2048
800h
-0.000
3071
0BFFh
-0.9990234
3072
0C00h
-1.000
3901090323
Rev 003
Page 12 of 25
0FFFh
-1.9990234
Data Sheet
Feb/12
MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
8 Temperature compensation
The MLX90323’s temperature compensation algorithm is piece-wise with up to 4 temperature segments, see
figure 2. Within each temperature segment (‘gap’), the correction is a first order calculation. There are
separate temperature coefficients for gain and offset. The first temperature gap is slightly different than the
other three. The compensation is based on the temperature difference between the current temp and the T1
point (the upper end of the gap). The other gaps use the lower end of the gap to measure the temperature
difference. For instance in the second gap, the temperature difference is current temperature minus T1. This
difference has to be accounted for in the compensation procedure.
Temperature Gaps
Temperature
Compensation
There are four temperature gaps possible with the
MLX90323. The gaps are defined with respect to
the filtered digitized temperature value saved in
RAM locations 58 and 59. The first temperature
gap is always bound at the low end by a digitized
temperature value of zero. The fourth
temperature gap is bound at the high end by a
digitized temperature value of 102310 (3FFhex).
OF & GN
OFTC4
OFTC3
OFTC2
Whenever fewer than four gaps are used, the last
gap should have an upper bound of 102310. This
is to ensure that if the temperature exceeds the
last point it won’t enter into an undefined
temperature gap.
GNTC4
GNTC3
Parameter
OFTC1
1 Gap
Temperature Points
GNTC2
i4
GNTC1
i3
i2
i1
0
Application's temperature
range
T1
T2
T3
3FFh
Temperature
Figure 2. Temperature Compensation.
The temperature points T1, T2 and T3 are defined
by the user to differentiate between the four
possible temperature compensation ranges. The
low endpoint T0 is defined as the minimum
digitized filtered temperature value, zero. This
means that the coefficients for the first gap,
OFTC1 and GNTC1, will apply to the signal until
the digitized filtered temperature reaches zero.
The high endpoint T4 is defined as the maximum
digitized filtered temperature value, 102310. This
means that the coefficients for the last gap,
OFTC4 and GNTC4 will apply to the signal from
the T3 point and up until the digitized filtered
temperature reaches its maximum, 102310.
When defining these points, the number that is
used is simply copied from the ‘Temp Value’ box
(see “MLX90323_software_descroption.pdf”) at
the desired temperature (contents of ram locations
58 and 59).
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Data Sheet
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MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
GNTC
The GNTC values are the gain temperature compensation values for each of the four temperature gaps,
GNCT1, GNTC2, GNTC3, and GNTC4. These values are used to adjust the signal up or down based on the
relative temperature within a particular gap. Mathematically this is represented by the following equation:
DAC_GAIN = CSGN * {GN[9:0] + [GNTCi *∆Ti]}
Where:
∆Ti = (T1 – temp_f) for gap 1;
∆Ti = (temp_f – Ti-1) for gaps 2,3,and 4;
Temp_f = Filtered temperature;
DAC_GAIN = The digital value that adjusts the gain on the gain amplifier;
Ti = Temperature segment point i = 2, 3, or 4;
GNTCi = Gain TC for a given temperature segment I;
CSGN = Course Gain;
GN[9:0] = Fixed Gain (doesn’t change with temperature).
The GNTC and OFTC values are 12 bit fixed point signed numbers (see table 4). That means that the most
significant bit is a sign bit. The next bit is one or zero (whole number). The remaining 10 bits are to the right
of the decimal point. This gives the variable the range of –1.9990234 to +1.9990234. The table below shows
how the fixed point numbers are represented as the binary number progresses from 0 to 4095.
OFTC
The OFTC values are the offset temperature compensation values for each of the four temperature gaps,
OFCT1, OFTC2, OFTC3, and OFTC4. These values are used to adjust the signal’s offset up or down based
on the relative temperature within a particular gap. The offset adjustment is additive from one gap to the
next. That is the offset adjustment for the fourth gap is added to the total offset adjustment of the third gap
which is also added to the total offset adjustment of the second gap. Mathematically this is represented by
the following equation:
For the first temperature gap:
DAC_OFFSET = OF[9:0] + OFTCi * (T1 – Temp_f)
For the second temperature gap:
DAC_OFFSET =OF[9:0] + OFTC2 * (Temp_f – T2)
For the third temperature gap:
DAC_OFFSET = OF[9:0] + [OFTC2 * (T2-T1)] + OFTC3 * (Temp_f – T3)
For the fourth temperature gap:
DAC_OFFSET =OF[9:0] + [OFTC2 * (T2-T1)] + [OFTC3 * (T3 – T2)] + OFTC4 * (Temp_f – T4),
Where OF[9:0] = Fixed offset
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Data Sheet
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MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
9 Calibration
9.1 Baseline Calibration
The baseline calibration involves setting the operating modes and temperature gain along with the coarse
and fixed gain and offset.
The operating modes are turbo mode, internal or external temperature sensor, and checksum test. The
checksum test, if used, should be enabled after all other settings are complete.
The invert signal bit swaps the differential inputs to the signal path. This has the same effect as swapping the
connections to the VBP and VBN pins of the chip.
Temperature amplifier gain, GNTP, should be set such that the analog converter doesn’t under-run or overrun at the temperature extremes. When using the internal temperature sensor over the full temperature span
of the device (-40C to +125°C) typically a GNTP setting of 2 will work. When using an external temperature
sensor the voltage on the TMP pin must stay within the ranges as described in the datasheet. The more of
the voltage range used the greater the temperature compensation adjustment range will be.
The coarse gain and fixed gain should be set before the coarse offset and fixed offset. Gain and offset are
inter-related, the offset is multiplied by the gain. It is much easier to program the gain first then offset. It may
be necessary to make some minor adjustment to the coarse offset settings before adjusting the gain. This is
only needed if the output clips at either high end or low end. It is difficult to precisely calculate the offset and
gain values. The amplifier circuitry within the chip uses resistors implemented in silicon. These resistors
have around a 20% tolerance, thus the gain and offset will vary from chip to chip. Each chip is tested to
provide a gain and offset adjustment capability within a specified range. For calculations a typical value can
be taken.
9.2 Temperature calibration
The temperature compensation capability of the MLX90323 is piece-wise with first order compensation in
each segment (gap). The compensation is based on the difference between the current digitized filtered
temperature and the appropriate temperature point. The equations have been previously described. The first
temperature gap is slightly different than the other three. The first gap uses the temperature difference
between the current temperature and the T1 temperature point (the upper end of the temperature gap). The
second temperature gap also uses the T1 point for determining the temperature differences (the low end of
the second gap). The third and fourth gaps also use the temperature point at the low end of their gap. This
means that programming the temperature compensation for the first gap is slightly different than the other
gaps. The compensation coefficients for the first gap (OFTC1 and GNTC1) apply to digitized filtered
temperature values from T1 down to zero. The fourth gap coefficients apply to digitized filtered temperature
range from T3 to 1023 (decimal).
The temperature points T1 thru T3 should always be in increasing order from T1 to T2 to T3. If the
temperature sensor has increasing signal with increasing temperature then the compensation procedure is
intuitively easy. This is the case with the internal temperature sensor. If the temperature sensor has
decreasing signal with increasing temperature then the compensation will start at a hotter temperature and go
towards cold. The procedure below is written with regard to the filtered digitized temperature not the real
physical temperature.
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Data Sheet
Feb/12
MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
9.3 Calibration procedure
1) Set the desired operating mode and number of gaps. It is also helpful to set T2 and T3 to 1023.
2) At the T1 temperature do a baseline calibration, the span then the offset by using CSGN[1:0] and GN[9:0]
then CSOF[1:0] and OF[9:0]. The T1 temperature is somewhat arbitrary, typically its room temperature. If
the temperature sensor goes down with increasing temperature then the T1 value will be towards the high
end of the application’s temperature range. Update the Temp value. Copy the digitized temperature reading
to the T1 box. If one temperature gap is desired then T1 will be the highest digitized temperature value.
3) Lower the temperature to the lowest operating temperature and recalibrate the output using
GNTC1 and OFTC1 only. If the temperature sensor goes down with increasing temperature then raise the
temperature to its maximum value and re-calibrate the output using GNTC1 and OFTC1. Do not change the
T1, OF, or GN values.
4) Raise the temperature until the second temperature point, T2. If the temperature sensor goes down with
increasing temperature then lower the temperature to the T2 value. This point may be arbitrary and can be
based on how far the output has deviated from it's desired value. Re-calibrate the sensor by adjusting
GNTC2 and OFTC2 only.
5) Update the Temp value displayed on the screen. Copy the digitized temperature value to the T2 box. This
must happen AFTER step 4.
6) Repeat steps 4 and 5 for T3 and setting GNTC3, OFTC3. T1, T2, and T3 must be in ascending order.
7) For the last temperature gap, raise the temperature to the highest operating temperature point and recalibrate the output using GNTC4 and OFTC4. There is no T4, it is assumed to be 1023 (the maximum value
of the digitized filtered temperature).
For less than four temperature gaps the last temperature point should be set to 1023. This means that the
last gap extends out to the end of the temperature range.
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Data Sheet
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MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
10 EEPROM and RAM byte definitions
Table 5. EEPROM Byte Definitions
Byte
Designation
Note
0
Turbo mode, temp
selection
Bit 0: must always be set to “1”
Bit 1: (0 = internal temp, 1 = external temp)
Bit 3: (0 = Turbo mode not active, 1 = active)
Bit 2,4,5,6: must always be set to “0”
Bit 7: (0 = EEPROM Checksum test inactive, 1 = active )
1
Cadj
Controls system clock during boot.
2
Coarse Control
Contents described in Table 6.
3
GN1L
The eight LSB's of the Fixed Gain, GN[7:0].
4
OF1L
The eight LSB's of Fixed Offset OF[7:0].
5
GNTC1L
The eight LSB's of the first gain TC GNTC1[7:0].
6
OFTC1L
The eight LSB's of the first offset TC OFTC1[7:0].
7
TR1L
The eight LSB's of the first temperature point, T1[7:0].
8
GNTC2L
The eight LSB's of the second gain TC GNTC2[7:0].
9
OFTC2L
The eight LSB's of the second offset TC OFTC2[7:0].
10
TR2L
The eight LSB's of the second temperature point T2[7:0].
11
GNTC3L
The eight LSB's of the third gain TC GNTC3[7:0].
12
OFTC3L
The eight LSB's of the third offset TC OFTC3[7:0]
13
TR3L
The eight LSB's of the third temperature point T3[7:0].
14
GNTC4L
The eight LSB's of the fourth gain TC GNTC4[7:0].
15
OFTC4L
The eight LSB's of the fourth offset TC OFTC4.
16
-
Reserved
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Data Sheet
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MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
Table 5. EEPROM Byte Definitions (continued)
Byte
Designation
Note
Upper four bits
Lower four bits
17
GN1[9:8]
OF1[9:8]
Two MSB's of fixed gain
GN[9:8].
Two MSB's of fixed offset
OF[9:8]
18
GNTC1[11:8]
OFTC1[11:8]
Four MSB's of first gain TC
GNTC1[11:8].
Four MSB's of the first offset
TC OFTC1[11:8].
19
TR1[9:8]
GNTC2[11:8]
Two MSB's, first temperature
point T1[9:8]
Four MSB's, second gain
TC GNTC2[11:8]
20
OFTC2[11:8]
TR2[9:8]
Four MSB's second offset
TC OFTC2[11:8]
Two MSB's second
temperature point T2[9:8]
21
GNTC3[11:8]
OFTC3[11:8]
Four MSB's third gain TC
GNTC3[11:8]
Four MSB's third offset
TC OFTC3[11:8]
22
TR3[9:8]
GNTC4[11:8]
Two MSB's third
temperature point t3[9:8]
Four MSB's fourth gain TC
GNTC4[11:8]
23
OFTC4[11:8]
Four MSB's fourth offset TC
reserved
24
PNB_TNB
Number of temperature gaps, see Table 7
25
n_factor
Temperature filter coefficient, four LSB's. Four MSB's must all
be zero.
-
26 - 31 reserved
reserved.
32
ClkTC1
Value of Cadj at low temperature (Don’t change; factory set).
33
ClkTC2
Value of Cadj at mid temperature (Don’t change; factory set).
34
ClkTC3
Value of Cadj at high temperature Don’t change; factory set).
35
Ctemp1
First Cadj temperature point, eight MSB’s of the 10 bit
internal temperature value (set at factory; do not change).
36
Ctemp2
Second Cadj temperature point, eight MSB’s of the 10 bit
internal temperature value (set at factory; do not change).
37-38
Not used
These bytes are not used and are available to the user.
39
CLKgntp
Setting for temperature amplifier for clock temperature
adjustment temperature reading (factory set, do not change).
3901090323
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Data Sheet
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MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
Table 5. EEPROM Byte Definitions (continued)
Byte
Designation
Note
40-41
Faultval
Value sent to output if checksum test fails is a 10 bit
value.
42-46
Not Used
These bytes are not used and are available to the user.
47
Checksum
EEPROM checksum; value needed to make all bytes
add to 0FFh. Must be set by user if checksum test is
active.
Table 6. Bit Definitions, Coarse Control , Byte 2
Bit Symbol Function
7
IINV
Invert signal sign.
Table 7. PNB_TNB Bit Definition
6
GNTP1 Gain & offset of temperature
amplifier.
5
GNTP0 GNTP = 0 to 3.
4
CSOF 1 Coarse offset of signal amplifier.
3
Maximum number of
temperature gaps
Maximum number of
signal gaps
Fixed Gain and
fixed Offset
5 Gaps
2 Gaps
3 Gaps
3 Gaps
2 Gaps
4 Gaps
Fixed signal
CSOF 0 CSOF = 0 to 3.
2
-
1
CSGN1
0
CSGN0
3901090323
Rev 003
Coarse gain of signal amplifier.
CSGN = 0 to 3.
Page 19 of 25
Data Sheet
Feb/12
MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
Table 8. RAM Byte Definitions
Byte
Functions
Remarks
0
Mode byte
1
GN1L
Fixed gain number (8LSB).
2
OF1L
Fixed offset number (8LSB).
3
GNTC1L
First gain TC (8LSB).
4
OFTC1L
First offset TC (8LSB).
5
TR1L
First temperature point.
6
GNTC2L
Second gain TC.
7
OFTC2L
Second offset TC.
8
TR2L
Second temperature point.
9
GNTC3L
Third gain TC.
10
OFTC3L
Third offset TC.
11
TR3L
Third temperature point.
12
GNTC4L
Fourth gain TC.
13
OFTC4L
Fourth offset TC.
14
-
reserved
Upper four bits
Lower four bits
15
GN1[9:8]
OF1[9:8]
Two MSB's of fixed gain
GN[9:8].
Two MSB's of fixed offset
OF[9:8].
16
GNTC1
[11:8]
OFTC1[11:8]
Four MSB's of first gain TC
GNTC1[11:8].
Four MSB's of the first
offset TC OFTC1[11:8]
17
TR1[9:8]
GNTC2[11:8]
Two MSB's, first temperature
point T1[9:8]
Four MSB's, second gain
TC GNTC2[11:8]
18
OFTC2[11:8]
3901090323
Rev 003
TR2[9:8]
Four MSB's, second offsetTC Two MSB's, second temp.
OFTC2[11:8]
point T2[9:8]
Page 20 of 25
Data Sheet
Feb/12
MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
Table 8. RAM Byte Definitions (continued)
Byte
Functions
Remarks
19
GNTC3[11:8] OFTC3[11:8]
20
TR3[9:8]
21
OFTC4[11:8]
22
PNB_TNB
Same as EEPROM.
23
n_factor
Temperature filter coefficient 4 LSB’s, 4 MSB = 0
24
Not Used
GNTC4[11:8]
-
Four MSB's, Third Gain TC
GNTC3[11:8]
Four MSB's Third Offset
TC OFTC3[11:8]
Two MSB's, third temperature
point t3[9:8]
Four MSB's, Fourth Gain
TC GNTC4[11:8]
Four MSB's Fourth Offset TC reserved
OFTC4[11:8]
25-26
GN
Offset Ordinate of the current gap.
27-28
OF
Gain Ordinate of the current gap.
Taddress
35-36
A_16
4 bits for the max. temperature address of the current gap;
4 bits for the min. temperature address of the current gap.
16 bits A Register.
37-38
B_16
16 bits B Register.
39-42
RESULT_32
32 bits result (for 16 bit multiplication).
43-44
Tempo1
Measured temperature, internal or external, and temporary
variable 1.
45
Tempo2
Temporary variable 2.
-
Reserved
48
Coms_backup
Address saved when command is send.
49
P3_copy
Port 3 setting copy.
50
Adsav1
Address saved at interrupt.
51-52
Aaccsav
A-Accumulators saved at interrupt.
53
Baccsav
B-Accumulators saved at interrupt.
54-55
DAC_gain
DAC gain (GN).
56-57
DAC_offset
DAC offset (OF).
58-59
Temp_f
60-61
-
Filtered temperature. This is a 10 bit number that is left
justified in a 16 bit field.
Reserved
62-63
Adsav2
Address saved when call.
29
46-47
Note: Because of space considerations, the measured temperature can’t be kept in the RAM at all times. If
the measured temperature is to be available, the temperature filter variable, n_factor, must be set to 6.
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Data Sheet
Feb/12
MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
11 Unique Features
Special Information
The output of the sensor bridge is amplified via offset and gain amplifiers and then converted to the correct
output signal form in one of the output stages.
The sensitivity and offset of the analog signal chain are defined by numbers passed to the DAC interfaces
from the microcontroller core (GN[9:0] and OF[9:0]). The wide range of bridge offset and gain is
accommodated by means of a 2-bit coarse adjustment DAC in the offset adjustment (CSOF[1:0]), and a
similar one in the gain adjustment (CSGN[1:0]). The signal path can be directed through the processor for
digital processing.
Programming and Setup
The MLX90323 needs to have the compensation coefficients programmed for a particular bridge sensor to
create the sensor system. Programming the EEPROM involves some minimal communications interface
circuitry, Melexis setup software, and a PC. The communications interface circuitry is available in a
development board. This circuitry communicates with the PC via a standard RS-232 serial communications
port.
12 Application Information
Supply
5K
VDD
FET VDD1
100 nF
COMS
100 nF
CMO
100 nF
VBP
75 Ohms
VBN
TMP
FLT
Depends on
stability of the
current loop
39 nF
GND CMN
24 Ohms
Ground
Figure 3. Typical application schematic
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Data Sheet
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MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
13 Standard information regarding manufacturability of Melexis products with
different soldering processes
Our products are classified and qualified regarding soldering technology, solderability and moisture sensitivity
level according to following test methods:
Reflow Soldering SMD’s (Surface Mount Devices)
•
•
IPC/JEDEC J-STD-020
Moisture/Reflow Sensitivity Classification for Nonhermetic Solid State Surface Mount Devices
(classification reflow profiles according to table 5-2)
EIA/JEDEC JESD22-A113
Preconditioning of Nonhermetic Surface Mount Devices Prior to Reliability Testing
(reflow profiles according to table 2)
Wave Soldering SMD’s (Surface Mount Devices) and THD’s (Through Hole Devices)
•
•
EN60749-20
Resistance of plastic- encapsulated SMD’s to combined effect of moisture and soldering heat
EIA/JEDEC JESD22-B106 and EN60749-15
Resistance to soldering temperature for through-hole mounted devices
Iron Soldering THD’s (Through Hole Devices)
•
EN60749-15
Resistance to soldering temperature for through-hole mounted devices
Solderability SMD’s (Surface Mount Devices) and THD’s (Through Hole Devices)
•
EIA/JEDEC JESD22-B102 and EN60749-21
Solderability
For all soldering technologies deviating from above mentioned standard conditions (regarding peak
temperature, temperature gradient, temperature profile etc) additional classification and qualification tests
have to be agreed upon with Melexis.
The application of Wave Soldering for SMD’s is allowed only after consulting Melexis regarding assurance of
adhesive strength between device and board.
Melexis is contributing to global environmental conservation by promoting lead free solutions. For more
information on qualifications of RoHS compliant products (RoHS = European directive on the Restriction Of
the use of certain Hazardous Substances) please visit the quality page on our website:
http://www.melexis.com/quality.aspx
3901090323
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Data Sheet
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MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
14 ESD Precautions
Electronic semiconductor products are sensitive to Electro Static Discharge (ESD).
Always observe Electro Static Discharge control procedures whenever handling semiconductor products.
15 Package Information
10.65
10.00
7.60
7.40
0.32
0.23
1.27
0.40
0.51
0.33
1.27
0o to
8o
Notes:
10.50
10.10
1. All dimensions in millimeters.
2. Body dimensions do not include mold flash or
protrusion, which are not to exceed 0.15mm.
2.65
2.35
0.010
min.
3901090323
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Data Sheet
Feb/12
MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
16 Disclaimer
Devices sold by Melexis are covered by the warranty and patent indemnification provisions appearing in its
Term of Sale. Melexis makes no warranty, express, statutory, implied, or by description regarding the
information set forth herein or regarding the freedom of the described devices from patent infringement.
Melexis reserves the right to change specifications and prices at any time and without notice. Therefore, prior
to designing this product into a system, it is necessary to check with Melexis for current information. This
product is intended for use in normal commercial applications. Applications requiring extended temperature
range, unusual environmental requirements, or high reliability applications, such as military, medical lifesupport or life-sustaining equipment are specifically not recommended without additional processing by
Melexis for each application.
The information furnished by Melexis is believed to be correct and accurate. However, Melexis shall not be
liable to recipient or any third party for any damages, including but not limited to personal injury, property
damage, loss of profits, loss of use, interrupt of business or indirect, special incidental or consequential
damages, of any kind, in connection with or arising out of the furnishing, performance or use of the technical
data herein. No obligation or liability to recipient or any third party shall arise or flow out of Melexis’ rendering
of technical or other services.
© 2012 Melexis NV. All rights reserved.
For the latest version of this document, go to our website at
www.melexis.com
Or for additional information contact Melexis Direct:
Europe, Africa, Asia:
Phone: +32 1367 0495
E-mail: [email protected]
America:
Phone: +1 248 306 5400
E-mail: [email protected]
ISO/TS 16949 and ISO14001 Certified
3901090323
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Data Sheet
Feb/12