MLX902xx Name of Sensor

Rev Y.X

22/Aug/98

Page 1

MLX90308CCC

Programmable Sensor Interface

MLX90308CCC Programmable Sensor Interface

Page 1

Rev 2.2 23/Oct/01

Features and Benefits

Microprocessor-controlled signal conditioning for bridge-type sensors
Suited for low-cost sensors: reduction of non-linearity by programmable coefficients
External or internal temperature sensor for compensating temperature errors
Versatile output signal ranges: 4, 5, 10, or 11V

; 4 to 20 mA loop

Mass calibration easy with 2400 or 9600 baud UART
Power supply from 6 to 35V

Applications

Pressure transducers
Accelerometers
Temperature sensor assemblies
Linear position sensors

Ordering Information

art No.

Temperature Suffix

Package

Option

Temperature Range

MLX90308CCC

-40C to 140C

MLX90308CCC

UD*

-40C to 140C

*UD denotes unpackaged die

Description

The MLX90308CCC is a dedicated microcontroller which performs signal conditioning for sensors wired in
bridge or differential configurations. Sensors that can be used include thermistors, strain gauges, load cells,
pressure sensors, accelerometers, etc. The signal conditioning includes gain adjustment, offset control, high
order temperature and linearity compensation. Compensation values are stored in EEPROM and are re-
programmable. Programming is accomplished by using a PC, with an interface circuit (level shifting and glue
logic), and provided software.

The application circuits can provide an
output of an absolute voltage, relative
voltage, or current. The output can be
range limited with defined outputs when
the signal is beyond the programmed
limits. Other features include alarm
outputs and level steering. The robust
e l e c t r i c a l d e s i g n a l l o w s t h e
MLX90308CCC to be used where most
signal conditioning and sensor interface
circuits cannot be used. Voltage
regulation control is provided for absolute
voltage and current modes (external FET
required).

The standard package is a plastic
SO16W. The device is static-sensitive and
requires ESD precautions.

MLX902xx Name of Sensor

Rev Y.X

22/Aug/98

Page 3

MLX90308CCC

Programmable Sensor Interface

MLX90308CCC Programmable Sensor Interface

Page 3

Rev 2.2 23/Oct/01

Table 1. MLX90308 Electrical Specifications

DC operating parameters: T

= -40 to 140

C, V

DD1

= 6 to 35V

(unless otherwise specified).

Parameter

Symbol Test Conditions

Min

Typ

Max Units

Regulator & Consumption
Input voltage range

DD1

(Regulator connected)

Supply current

@ T

= 100�C Current Mode

2.1

Supply current

@ T

= 100�C Voltage Mode

5.0

Regulated supply voltage

REG

4.5

4.75

5.2

Regulated voltage
temperature coefficient

-600

uV /

�

Supply rejection ratio

PSRR

DD1

> 6V

Instrumentation Amplifier

Differential input range

VBP-VBN IINV = 0

-11.0

32.0 mV/V

(Vdd)

Differential input range

VBP-VBN IINV = 1

-32.0

11.0 mV/V

(Vdd)

Common mode input range

1/2(VBP+VBN)

38.0

65.0 %VDD

Pin leakage current

Pins VBP & VBN to GND, V

8.0

Common mode rejection

CMRR

Hardware gain

V/V

Coarse offset control Range

CSOF[1:0] = 00

-15.3

-13.9 mV/V

CSOF[1:0] = 01

-5.1

-3.8 mV/V

CSOF[1:0] = 10

3.8

5.1

mV/V

CSOF[1:0] = 11

13.9

15.3 mV/V

Fixed offset control range

High

6.0

8.0

mV/V

Low

-7.0

-5.0 mV/V

IA chopper frequency

300

kHz

Gain Stage

Course gain

CSGN = 000

3.0

3.3

V/V

(Fixed Gain = 1023)

CSGN = 001

4.9

5.4

V/V

CSGN = 010

8.0

8.8

V/V

CSGN = 011

12.8

14.1 V/V

CSGN = 100*

7.9

8.7

V/V

CSGN = 101*

12.7

14.0 V/V

* CSGN = 100 to 111: voltage mode
only, not applicable to current mode.
Output > 6.5V; MSB = 1
Output < 6.5V; MSB = 0

MLX90308CCC

Programmable Sensor Interface

MLX90308CCC Programmable Sensor Interface

Page 4

Rev 2.2 23/Oct/01

Table 1. MLX90308 Electrical Specifications (continued)

DC operating parameters: T

= -40 to 140

C, V

DD1

= 6 to 35V

(unless otherwise specified).

Parameter

Test Conditions

Min

Typ

Max

Units

Coarse gain

CSGN = 110*

20.4

23.0

V/V

CSGN = 111*

33.1

36.6

V/V

Fixed gain control range

0.480

0.970

V/V

Digital Mode & Current Mode Coarse Gain Stage

Course Gain

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

Output voltage span

CSGN[2:2] = 0

4.5

6.5

Gain

2.74

3.04

V/V

CSGN[2:2] = 1

6.5

Gain

7.24

7.86

V/V

Minimum output voltage

-0.2

Output source current

2.0

Output sink current

@ 0V output voltage

Output resistance

Over complete output range

Ohms

Digital mode output span

CSGN[2:2] = 0

6.5

CSGN[2:2] = 1

11.0

Digital mode step size

= 5V, CSGN[2:2]=0

6.5

= 5V, CSGN[2:2]=1

11.0

Capacitive load VMO pin

Current Mode Output Stage
Fixed gain

SENSE

= 24 ohm

8.4

9.3

mA/V

Output current CMO pin

Current mode

Current sense resistor

Ohms

Digital mode current output span

= 5V

Digital mode current step Size

= 5V,R

SENSE

=24�

Signal Path ( General)
Overall gain

Voltage mode

600

V/V

Current mode = 24�

750

mA/V

Overall non-linearity

-0.25

0.25

Ratiometry Error (4.75V � 5.25V)

Overall Gain < 250V/V

-0.5

0.5

Overall Gain > 250V/V

-1.3

+1.3

Voltage Mode Output Stage ( See Voltage Mode)

MLX902xx Name of Sensor

Rev Y.X

22/Aug/98

Page 5

MLX90308CCC

Programmable Sensor Interface

MLX90308CCC Programmable Sensor Interface

Page 5

Rev 2.2 23/Oct/01

Table 1. MLX90308 Electrical Specifications (continued)

DC operating parameters: T

= -40 to 140

C, V

DD1

= 6 to 35V

(unless otherwise specified).

Parameter

Test Conditions

Min

Typ

Max Units

Bandwidth (-3dB)

39 nF connected from FLT to GND 2.8

3.5

4.2

KHz

5.0

mVRMS

Temperature Sensor & - Amplifier

Temperature sensor sensitivity

390

uV/�C

Temperature sensor output voltage

380

Temperature Sensor & Amplifier (continued).
Input voltage range TMP pin

GNTP[1,0] = 00

207

517 mV

@ V

= 5.0V

GNTP[1,0] = 01

145

367 mV

GNTP[1,0] = 10

101

263 mV

GNTP[1,0] = 11

186 mV

DAC
Resolution

Bit

Monotonicity

Guaranteed By Design

Ratiometric output range (DAC output)

% V

Offset Error

LSB

Differential non-linearly

LSB

Integral non-linearity

LSB

ADC
Resolution

Bit

Monotonicity

Guaranteed by design

Ratiometric input range

% V

Offset error

LSB

Differential non-linearly

LSB

Integral non-linearity

LSB

On-Chip RC Oscillator and Clock
Untrimmed RC oscillator
frequency

250 kHz

Trimmed RC oscillator frequency
(Measured at TMP pin with TSTB pin pulled low after power up)

86.9

87.8

88.7 kHz

Frequency temperature coefficiency

Hz/�C

Clock Stability with temperature compensation over full temperature range

-3

Ratio of f (microcontroller main clock
and (RC oscillator)

TURBO = 0

TURBO = 1

Noise, V

= 5V, C

FLT

=39nF, C

=10nF, R

=5K�,

Analog Mode

MLX90308CCC

Programmable Sensor Interface

MLX90308CCC Programmable Sensor Interface

Page 6

Rev 2.2 23/Oct/01

Table 1. MLX90308 Electrical Specifications (continued)

DC operating parameters: T

= -40 to 140

C, V

DD1

= 6 to 35V

(unless otherwise specified).

Parameter

Test Conditions

Min

Typ

Max Units

Input & Output Pins (I01 & I02)

Digital input levels

Low

0.5

High

-0.5

Output Levels

@ output current = 5mA low

-0.4

0.4

@ Output current = 5mA high

TSTB Pin
Input levels

Low

0.5

High

-0.5

Pull-up Resistor

kOhms

FLT Pin
Output resistance

1.24

kOhms

Output voltage range

VDD = 5V

0.05

3.6

OFC Pin
Output voltage range

VDD = 5V

0.05

3.75

Load capacitor

UART & COMS Pin
UART baud rate

TURBO = 0

2400

baud

TURBO = 1

9600

baud

COMS pin input levels

Low

0.3*V

High

0.7*V

COMS Pin Output Resistance

Low

100

Ohms

High

100

kOhms

MLX902xx Name of Sensor

Rev Y.X

22/Aug/98

Page 7

MLX90308CCC

Programmable Sensor Interface

MLX90308CCC Programmable Sensor Interface

Page 7

Rev 2.2 23/Oct/01

Table 2. Absolute Maximum Ratings

Supply voltage (ratiometric) V

Max

Supply voltage (ratiometric) V

Min

4.5V

Supply voltage (operating),

DD1

Max

35V

Reverse voltage protection

-0.7V

Supply current, Current Mode, I

3.5mA

Supply current, Voltage Mode, I

4.5mA

Output current, I

VMO

8mA

Output current (short to V

), I

SCVMO

100mA

Output current (short to V

), I

SCVMO

8mA

Output voltage, V

VMO

+11V

Power dissipation, P

71mW

Operating temperature range, T

-40 to +140�

Storage temperature range, T

-55 to +150�C

Maximum junction temperature, T

150�C

Unique Features

Customization

Melexis can customize the MLX90308 in both
hardware and firmware for unique requirements.
The hardware design provides 64 bytes of RAM, 3
kbytes of ROM, and 48 bytes of EEPROM for use
by the firmware.

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[2:0]). The signal path can be directed
through the processor for digital processing. Two I/
O pins are available for analog inputs or digital
outputs. These pins can be used for alarms on
various points on the analog signal path and built-in
or external temperature values.

Programming and Setup

The MLX90308 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.

Cross Reference

There are no known devices which the MLX
90308CCC can replace.

ESD Precautions

Observe standard ESD control procedures for
CMOS semiconductors.

MLX90308CCC

Programmable Sensor Interface

MLX90308CCC Programmable Sensor Interface

Page 8

Rev 2.2 23/Oct/01

Signal
Name

Description

1,2 I/O1, 2

Bi-directional I/O. Can also be used as input to A/D converter. I/O can be
controlled by serial communications or by firmware as alarm inputs or level
out. (unconnected when not used)

TSTB

Test pin for Melexis production testing. (in normal application connected to
VDD)

FLT

Filter pin; allows for connection of a capacitor to the internal analog path.

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.

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.

Regulated supply voltage. Used for internal analog circuitry to ensure
accurate and stable signal manipulation.

FET

Regulator FET gate control. For generating a stable supply for the bridge
sensor and internal analog circuitry (generates regulated voltage for VDD).

DD1

Unregulated supply voltage. Used for digital circuitry and to generate FET
output.

VMO

Voltage mode output. Compensated sensor output voltage.

CMO

Current mode output. Compensated sensor output for current mode
operation.

CMN

Current mode negative rail. Current mode return path.

GND

Power supply return.

COMS

Serial communications pin. Bi-directional serial communication signal for
reading and writing to the EEPROM.

Table 3. Pin Description

IO1

IO2

TSTB

FLT

OFC

VBN

VBP

TMP

COMS

GND

CMN

CMO

VMO

VDD1

FET

VDD

Figure 2. Pinout (SO16W (LW) Package)

MLX902xx Name of Sensor

Rev Y.X

22/Aug/98

Page 9

MLX90308CCC

Programmable Sensor Interface

MLX90308CCC Programmable Sensor Interface

Page 9

Rev 2.2 23/Oct/01

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). For ratiometric operation, the
supply-regulator can be disabled by connecting
together the unregulated and regulated supply pins.

Oscillator

The MLX90308 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.

A/D and D/A

Conversions using only one DAC

For saving chip area, the "Offset DAC" is
multiplexed in various ways. Both "fine offset" and
"digital mode" signals are stored on a capacitor. An
ADC-loop is available by using a comparator and
SAR.

D/A

Before changing to another capacitor, the DAC
output should be settled to the new value. For
example, MODSEL moves the analog multiplexer to
the so-called "open state 0." At the same time, the
10 bit mux selects OF[9:0] for the offset-DAC. After
the DAC settling time, the analog multiplexer is
moved to its final state and the DAC-output is stored
on a capacitor.

A/D

The S/W-Signal MODSEL connects the SAR-output
to the DAC and the DAC-output to the comparator.
The SARegister is initialized by a rising edge of STC
(S/W signal). At the end of the A/D conversion, the
EOC flag is set to 1 and the controller can read the
ADC values.

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.

Test Mode

For 100% testability, a "TEST" pin is provided. If the
pin is pulled low, then the monitor program is entered
and the chip changes its functionality. In all other
applications, this pin should be pulled high or left
floating (internal pull-up).

Temperature Sense

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.

MLX90308CCC

Programmable Sensor Interface

MLX90308CCC Programmable Sensor Interface

Page 10

Rev 2.2 23/Oct/01

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.

Firmware

The MLX90308 firmware performs the signal
conditioning by either of two means: analog or
digital. The analog signal conditioning allows
separate offset and gain temperature coefficients for
up to four temperature ranges. Digital mode allows
for all of the analog capabilities plus up to five
different gain values based on the input signal level.
Also available in both modes is the capability of
r a n g e l i m i t i n g a n d l e v e l s t e e r i n g .

Temperature Processing

In both analog and digital modes, the 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
Temp_f(n+1) =

Temp_f(n) - [measured_temp -

Temp_f(n)] [2

n_factor

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.

Digital Features

Microprocessor, LX11 Core, Interrupt
Controller, Memories

The LX11 microcontroller core is described in its
own datasheet. As an overview, this implementation
of the LX11 RISC core has following resources:

Two accumulators, one index and two interrupt
accumulators.
15 - 8 bit I/O ports to internal resources.
64 byte RAM.
4 kbytes ROM : 3 kbytes is available for the
customer's application firmware. 1k is
reserved for test.
48 x 8 bit EEPROM.
Four interrupt sources, two UART interrupts
and two timers.

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 STOP-bit 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.

MLX902xx Name of Sensor

Rev Y.X

22/Aug/98

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MLX90308CCC

Programmable Sensor Interface

MLX90308CCC Programmable Sensor Interface

Page 11

Rev 2.2 23/Oct/01

Different Modes

Analog Mode

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.

Vout =

FG * DAC_GAIN * CSGN[2:0] *

{Vin+DAC_OFFSET+CSOF}

Iout =

FG * DAC_GAIN * CSGN[1:0] *

{Vin+DAC_OFFSET+CSOF} * 8.85mA/V

FG = Hardware Gain (~20V/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.

GAIN

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)

3th 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]

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.

[mV/V]

Digital Mode

The MLX90308 firmware provides the capability of
digitally processing the sensor signal in addition to
the analog processing. This capability allows for
signal correction.

Signal Correction

While in digital mode the firmware can perform
signal correction. This is an adjustment to the
output level based on the input signal level.
Adjustment coefficients can be set for five different
signal ranges. The output is obtained by the
following formula:

Output = (Signal � Pi) * Pci + Poff where
Signal = input signal measurement;
Poff = Pressure ordinate
Pi = Pressure signal point (I = 2,3,4,5)
Pci = programmed coefficient.

The PCi coefficients are coded on 12 bits: one bit for
the sign, one for the unity, and the rest for the
decimals. The Pi are coded on 10 bits (0-3FFh) in
high-low order.

PNB_TNB: contains the number of signal points,
coded on the four MSB's. The four LSB's are
reserved for the number of temperature points. See
Table 4 and Table 5.

Compensation Trade-Offs

A compromise must be made between temperature
compensation and pressure correction. The
EEPROM space where the signal coefficients are
stored is shared with the temperature coefficients,
with the result that an EEPROM byte can be used
either for a temperature coefficient or for a signal
coefficient, but not both. Table 6 presents the
possibilities among the maximum number of
temperature gaps and the maximum number of
signal gaps.

GAIN

DAC

1023

]

[

)

(

OFFSET

DAC

1023

]

[

)

(

MLX90308CCC

Programmable Sensor Interface

MLX90308CCC Programmable Sensor Interface

Page 12

Rev 2.2 23/Oct/01

Table 4. PNB_TNB Bit Definition;

Table 5. PNB_TNB Bit Definition;

Temperature Gaps

# of Temperature Gaps

4 LSB of PNB_TNB

Fixed (1)

2 Gaps

3 Gaps

4 Gaps

11 (B hex)

# of Pressure Gaps

4MSB of PNB_TNB Value

Fixed

15 (F hex)

14 (E hex)

12 (C hex)

10 (A hex)

Table 6. Temperature

Parameter

Figure 3. Temperature

Linearity Correction

OF & GN

MLX90308

GN0

OF0

3FFh

GNTC4

GNTC3

GNTC2

GNTC1

OFTC1

OFTC2

OFTC3

OFTC4

1 Gap

Baseline Calibration

Output (units)

Figure 4. Signal

Linearity Correction

Output

MLX90308

PC1

PC2

PC3

PC4

PC5

Maximum number of

temperature gaps

Maximum number of

signal gaps

Fixed Gain and

fixed Offset

5 Gaps

2 Gaps

3 Gaps

2 Gaps

4 Gaps

Fixed signal

MLX902xx Name of Sensor

Rev Y.X

22/Aug/98

Page 13

MLX90308CCC

Programmable Sensor Interface

MLX90308CCC Programmable Sensor Interface

Page 13

Rev 2.2 23/Oct/01

Figure 5.
Alarm Function

OUTPUT

Output

Input Signal

MLX90308

Low

Output

Low

Trigger

High

Trigger

High

Output

Selected input

MUX Value

TPO

0010

IAO

0110

GNO

0000

VMO

0011

IO1

0100

IO2

0101

Table 7. Alarm Source Bit Definition

Figure 6.
Alarm & Steering
Source Points

VMO

CMO

CMN

TSTB

Gain

Offset

Power Supply

Regulation

Temp

Sense
& Amp

Bidirectional

I/O

ADC

DAC

UART

Microcontroller
Core, Memory,

EEPROM

Reset,Test,&

Oscillator

OFC

FLT

VDD1 FET VDD GND

COMS

IO2

IO1

TMP

VBN

VBP

IAO

GNO

TPO

Alarm Option

This option allows controlling the low and high limits
of the output (See Figure 5.). The output level is set
when the output tries to exceed the programmed
limits. Five bytes are reserved for this option. The
first byte is the low trigger limit and the second the
low output. The third and fourth bytes are used for
the high limit and the output. The fifth byte is the
alarm control, used to select the alarm input. The
different levels are programmed as eight bit
numbers. These correspond to the 8 upper bits of
the 10 bit signal measurement. When the alarm
mode is not used, all of the data is 0. The control
code is coded as shown in Table 7. The six possible
signals are listed below and are encoded on the 4
MSB's of byte 31 of the EEPROM.

IO1 & IO2

IO1 and IO2 are used in the alarm and level
steering modes. For custom firmware, they can be
used for a digital input, an analog input, or a digital

Figure 7. Level Steering
Function

IO1, IO2

Parameter

MLX90308

Level 1

1 -1

1 - 0

0 - 1

0 - 0

(I02,I01)

Level 2

Level 3

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Programmable Sensor Interface

MLX90308CCC Programmable Sensor Interface

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Bit

Function

Remarks

1= EEPROM Checksum test active
0= EEPROM Checksum test inactive

EEPROM Checksum test. Checksum test failure will
force the output to the value programmed in bytes 40
and 41 of the EEPROM (See Table 10).

0 = Analog Mode
1 = Digital Mode

Digital mode must be activated when VMO and CMO
both active.

0 = Alarm function inactive
1 = Alarm function active

Alarm functions are like "limiting functions":
If defined ADC INPUT is below low alarm trigger,
then DIGMOD becomes active with alarm low
output).
If defined ADC INPUT is above high alarm trigger,
then DIGMOD becomes active with alarm high
output.
Note: Deactivated if the level steering mode is active

0 = IO1/IO2 are not active outputs
1 = level steering: IO1/IO2 are active
outputs

Depending on the sampled input, IO1/IO2 will be a
two bit digital output. If IO1/IO2 are not active
outputs, then they will be analog inputs.

0 = Turbo inactive
1 = Turbo active

0 = VMO inactive
1 = VMO active

0 = Internal temperature sensor active
1 = External temperature sensor
active

0 = CMO inactive
1 = CMO active

CMO has fixed digital value (EEPROM byte - see
below) if both VMO and CMO are active. To activate
this value, the digital mode must be activated.

Table 9. Mode Byte Bit Definition

Level Steering

The level steering option allows configuration of the
IO pins as outputs to indicate the relative level of a
selected signal. See Figure 7. The levels at which
the two outputs change state are programmed by
the user. The programmed levels are set as eight bit
numbers and compared to the upper eight bits of
the digitized signal. This function utilizes the same
resources as the alarm function. The two functions
(level steering and alarm) can not be used
simultaneously. Four bytes in the EEPROM
command this option. The first byte is used to select
the input, while the last three comprise the transition
levels. The control byte for the level steering is the
same as for the alarm. The four MSB's hold the
code for the selected input. The control byte has
several possibilities as designated by the MUX
settings (See Table 8)

Communications

The MLX90308 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 and digitized GNO. The commands are
described below. Melexis provides setup software
for programming the MLX90308.

Selected input

MUX Value

TPO

0010

IAO

0110

GNO

0000

VMO

0011

Table 8. Level Steering Bit Definitions

MLX902xx Name of Sensor

Rev Y.X

22/Aug/98

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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.
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:

11 to read a RAM byte.

10 to read an EEPROM byte.

01 to write in the EEPROM.

00 to write in the RAM.

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 MLX90308CCC. The EEPROM
is always re-programmable. 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.

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 (pressure, temperature) 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.

MLX90308CCC

Programmable Sensor Interface

MLX90308CCC Programmable Sensor Interface

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Rev 2.2 23/Oct/01

Byte

Designation

Note

MODE byte

Contents described in Table 9.

Cadj

Controls system clock during boot.

Coarse Control

Contents described in Table 12.

GN1L

The eight LSB's of the Fixed Gain, GN[7:0].

OF1L

The eight LSB's of Fixed Offset OF[7:0].

GNTC1L

The eight LSB's of the first gain TC GNTC1[7:0].

OFTC1L

The eight LSB's of the first offset TC OFTC1[7:0].

TR1L
PC5L

The eight LSB's of the first temperature point, T1[7:0].
The eight LSB's of Pressure Coefficient 5 PC5[7:0].

GNTC2L
P5L

The eight LSB's of the second gain TC GNTC2[7:0].
The eight LSB's of Pressure Point 5 P5[7:0].

OFTC2L
PC4L

The eight LSB's of the second offset TC OFTC2[7:0].
The eight LSB's of Pressure Coefficient 4 PC4[7:0].

TR2L
P4L

The eight LSB's of the second temperature point T2[7:0].
The eight LSB's of Pressure Point 4 (or Signature) P4[7:0].

GNTC3L
PC3L

The eight LSB's of the third gain TC GNTC3[7:0].
The eight LSB's of Pressure Coefficient 3 (or Signature) PC3
[8:0].

Table 11. EEPROM Byte Definitions

Decimal

Hexadecimal
Equivalent

Fixed Point Signed
Number Equivalent

0000h

+0.00

1023

3FFh

+0.9990234

1024

400h

+1.000

2047

7FFh

+1.9990234

2048

800h

-0.000

3071

0BFFh

-0.9990234

3072

0C00h

-1.000

4095

0FFFh

-1.9990234

Table 10. Examples of Fixed Point
Signed Numbers

Data Range

Various data are arranged as follows:

Temperature points: 10 bits, 0-03FF in high-

low order.

Pressure 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].

Pci: signed 12 bits (with MSB for the sign),

[-1.9990234, +1.9990234]

DIGMO: 10 bits, 0-03FF in high-low order
(See Table 13 for examples of fixed point

MLX902xx Name of Sensor

Rev Y.X

22/Aug/98

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Byte

Designation

Note

OFTC3L or

P3L

The eight LSB's of the third offset TC OFTC3[7:0].

The eight LSB's of Pressure Point 2 (or Signature) P2[7:0].

TR3L or
PC2L

The eight LSB's of the third temperature point T3[7:0].
The eight LSB's of Pressure Coefficient 2 PC2[7:0].

GNTC4L or
P2L

The eight LSB's of the fourth gain TC GNTC4[7:0].
The eight LSB's of Pressure Point 2 P2[7:0].

OFTC4L or
PC1L

The eight LSB's of the fourth offset TC OFTC4.
The eight LSB's of Pressure Coefficient 1 PC1

PoffL

The eight LSB's of Pressure (output signal) Ordinate Poff[7:0].

Upper Lower
Four Four
Bits Bits

Upper four bits. Lower four bits

GN1[9:8] OF1[9:8]

Two MSB's of fixed gain Two MSB's of fixed offset
GN[9:8]. OF[9:8]

GNTC1[11:8] OFTC1[11:8]

Four MSB's of first gain TC Four MSB's of the first offset
GNTC1[11:8]. TC OFTC1[11:8].

TR1[9:8] GNTC2[11:8]

PC5[11:8] P5[9:8]

Two MSB's, first temperature Four MSB's, second gain
point T1[9:8] or TC GNTC2[11:8] or
Four MSB's, Pressure TC GNTC2[11:8] or
Coefficient 5 PC5[11:8]. Two MSB's Pressure Point 5
P5[9:8].

OFTC2[11:8] TR2[9:8]

PC4[11:8] P4[9:8]

Four MSB's second offset Two MSB's second
TC OFTC2[11:8] or temperature point T2[9:8] or
Four MSB's Pressure Two MSB's Pressure Point 4
Coefficient 4 PC4[11:8]. P4[9:8].

GNTC3[11:8] OFTC3[11:8]

PC3[11:8] P3[9:8]

Four MSB's third gain TC Four MSB's third offset
GNTC3[11:8] or TC OFTC3[11:8] or
Four MSB's Pressure Two MSB's Pressure Point 3
Coefficient 3 PC3[11:8]). P3[9:8].

TR3[9:8] GNTC4[11:8]

PC2[9:8] P2[9:8]

Two MSB's third Four MSB's fourth gain TC
temperature point t3[9:8] or GNTC4[11:8] or
Four MSB's Pressure Two MSB's Pressure
Coefficient 2 PC2[11:8]. Point 2 P2[9:8].

OFTC4[11:8] Poff[9:8]

PC1[11:8]

Four MSB's fourth offset TC Two MSB's Pressure
ordinate
OFTC4[11:8] or Poff[9:8].
Four MSB's Pressure
Coefficient 1 PC1[11:8].

Table 11. EEPROM Byte Definitions (continued)

MLX90308CCC

Programmable Sensor Interface

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Rev 2.2 23/Oct/01

Byte

Designation

Note

PNB_TNB

Number of temperature and pressure gaps. See Tables 4, 5,
and 6, and Figures 3 and 4.

n_factor

Temperature filter coefficient, four LSB's. Four MSB's must
all be zero.

Not used

This byte is not used.

ALARM low trigger
Level1 IO2/IO1

Value below which ALARM will go on.
Value of first level ([IO2, IO1]= 00-01). See Figures 5 & 7.

ALARM low output
Level2 IO2/IO1

Value of DIGMO during "ALARM low" condition.
Value of second level ([IO2,IO1] = 01-10). See Figures 5
and 7

ALARM high trigger
Level3 IO2/IO1

Value above which ALARM will go on.
Value of third level ([IO2,IO1]=10-11). See Figures 5 and 7.

ALARM high out level

Value of DIGMO during "ALARM high" condition. See
Figures 5 and 7.

ALARM control byte

IO1/IO2 control byte

Four LSB's are unused

Three bits needed for choice of input for ALARM detection
(TPO, IAO, GNO, VMO, IO1 or IO2).

Two bits needed for choice of input for LEVEL-steering
(TPO, IAO, GNO or VMO).

The above bits are multiplexed according to the mode. If
both CMO and VMO are active, then alarm is not active.

ClkTC1

Value of Cadj at low temperature (Don't change; factory set).

ClkTC2

Value of Cadj at mid temperature (Don't change; factory
set).

ClkTC3

Value of Cadj at high temperature Don't change; factory set).

Ctemp1

First Cadj temperature point, eight MSB's of the 10 bit
internal temperature value (set at factory; do not change).

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 by the firmware and are available
to the user.

CLKgntp

Setting for temperature amplifier for clock temperature
adjustment temperature reading (set at factory; do not
change).

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 by the firmware and are available
to the user.

Checksum

EEPROM checksum; value needed to make all bytes add to
0FFh. Must be set by user if checksum test is active.

Table 11. EEPROM Byte Definitions (continued)

MLX902xx Name of Sensor

Rev Y.X

22/Aug/98

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MLX90308CCC

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Notes For Table 11

1. Not all the temperature and pressure coefficients
must be used. When a coefficient is unused, the
eight LSB's and the four MSB's are replaced by 0.

2. The level steering and the alarm mode cannot be
active simultaneously because the levels bytes are
shared with the two modes.

3. If the alarm mode and the level steering are both
active, the level steering mode is dominant. The
firmware will run with the level steering mode, by
default.

4. If the DIGMO mode (VMO and CMO both active)
is active, the alarm will be automatically disabled by
the firmware.

5. At PNB_TNB address, the four MSB's correspond
to the address of the last pressure point and the four
LSB's to the address of the last temperature point.

6. In the alarm_control variable, the selected
input is stored on the three MSB's.

7. Pi and OFi are 10 bit values, right justified in 12
bits fields.

Table 12. Bit Definitions;
Coarse Control , Byte 2

Bit Symbol Function

IINV

Invert signal sign.

GNTP1 Gain & offset of temperature

amplifier.

GNTP0 GNTP = 0 to 3.

CSOF 1 Coarse offset of signal amplifier.

CSOF 0 CSOF = 0 to 3.

CSGN2

CSGN1

CSGN0

Coarse gain of signal amplifier.
CSGN = 0 to 7. If CSGN > 3,
output range = 0 to 10V. If
CSGN <= 3, output range = 0 to
5V.

Byte

Functions

Remarks

MODE byte

See Table 9.

GN1L

Fixed gain number (8LSB).

OF1L

Fixed offset number (8LSB).

GNTC1L

First gain TC (8LSB).

OFTC1L

First offset TC (8LSB).

TR1L
PC5L

First temperature point.
Pressure Coefficient 5 (8LSB).

GNTC2L
P5L

Second gain TC.
Pressure point 5 (8LSB).

OFTC2L
PC4L

Second offset TC.
Pressure coefficient 4 (8LSB).

TR2L
P4L

Second temperature point.
Pressure Point 4 (or Signature) (8LSB).

GNTC3L
PC3L

Third gain TC.
Pressure Coefficient 3 (or Signature) (8LSB).

OFTC3L
P3L

Third offset TC.
Pressure Point 2 (or Signature) (8LSB).

Table 13. RAM Byte Definitions

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Programmable Sensor Interface

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Rev 2.2 23/Oct/01

Table 13. RAM Byte Definitions (continued)

Byte

Functions

Remarks

TR3L

PC2L

Third temperature point.

Pressure Coefficient 2 (8LSB).

GNTC4L

P2L

Fourth gain TC.

Pressure Point 1 (8LSB).

OFTC4L

PC1L

Fourth offset TC.

Pressure Coefficient 1 (8LSB).

DIGMOP1L

Fixed pressure (8LSB).

GN1[9:8] OF1[9:8]

Two MSB's of fixed gain Two MSB's of fixed offset
GN[9:8]. OF[9:8].

GNTC1 OFTC1
[11:8] [11:8]

Four MSB's of first gain TC Four MSB's of the first
GNTC1[11:8]. offset TC OFTC1[11:8]

TR1[9:8] GNTC2
[11:8]

PC5[11:8] P5[9:8]

Two MSB's, first temperature Four MSB's, second gain
point T1[9:8] or TC GNTC2[11:8] or

Four MSB's Pressure Two MSB's, Pressure
Coefficient 5 PC5[11:8]. Point 5 P5[9:8]

OFTC2[11:8]

TR2

[9:8]

PC4[11:8] P4[9:8]

Four MSB's, second offset TC Two MSB's, second temp.
OFTC2[11:8] or point T2[9:8] or

Four MSB's, Pressure Two MSB's, Pressure
Coefficient 4 PC4[11:8]. Point 4 P4[9:8].

GNTC3[11:8] OFTC3
[11:8]

PC3[11:8] P3[9:8]

Four MSB's, Third Gain TC Four MSB's Third Offset
GNTC3[11:8] or TC OFTC3[11:8] or

Four MSB's, Pressure Two MSB's Pressure
Coefficient 3 PC3[11:8]). Point 3 P3[9:8]

TR3[9:8]

GNTC4

[11:8]

PC2[9:8] P2[9:8]

Two MSB's, third temperature Four MSB's, Fourth Gain
point t3[9:8] or TC GNTC4[11:8] or

Four MSB's, Pressure Two MSB's, Pressure
Coefficient 2 PC2[11:8]. Point 2 P2[9:8].

OFTC4[11:8]

P1[9:8]

PC1[11:8]

Four MSB's Fourth Offset TC Two MSB's Pressure
OFTC4[11:8] or Point 1 P1[9:8].

Four MSB's Pressure
Coefficient 1 PC1[11:8].

PNB_TNB

Same as EEPROM.

N_Factor

Temperature filter coefficient -- 4 LSB's, 4 MSB = 0

Not Used

25-26

Offset Ordinate of the current gap.

27-28

Gain Ordinate of the current gap.

Taddress

4 bits for the max. temperature address of the current gap; 4
bits for the min. temperature address of the current gap.

MLX902xx Name of Sensor

Rev Y.X

22/Aug/98

Page 21

MLX90308CCC

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Rev 2.2 23/Oct/01

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.

Table 13. RAM Byte Definitions (continued)

Byte

Functions

Remarks

ALARM control byte
IO1/IO2 control byte

Three bits needed for choice of input for ALARM detection
(TPO, IAO, GNO, VMO, IO1 or IO2). Two bits needed for
choice of input for LEVEL-steering (TPO, IAO, GNO or
VMO). These bits are multiplexed according the mode.
Note: if both CMO and VMO are active, then alarm is not
active.

ALARM low trigger level

IO1/IO2 level 1

Value below which ALARM will go on.

Value of first level ([IO2,IO1]=00-01).

ALARM low output level

IO1/IO2 level 2

Value of DIGMO during "ALARM low" condition.

Value of second level ([IO2,IO1]=01-10).

ALARM high trigger
level

IO1/IO2 level 3

Value above which ALARM will go on.

Value of third level ([IO2,IO1] = 10-11).

ALARM high output
level

Value of DIGMO during "ALARM high" condition.

35-36

A_16

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.

Tempo2

Temporary variable 2.

46-47

Signal_In

Digitized signal value, analog and digital mode

Coms_backup

Address saved when command is send.

P3_copy

Port 3 setting copy.

Adsav1

Address saved at interrupt.

51-52

Aaccsav

A-Accumulators saved at interrupt.

Baccsav

B-Accumulators saved at interrupt.

54-55

DAC_gain

DAC gain (GN).

56-57

DAC_offset

DAC offset (OF).

58-59

Temp_f

Filtered temperature. This is a 10 bit number that is left justi-
fied in a 16 bit field.

60-61

Signal_Out

Digitized linearity corrected signal value. Digital mode only.

62-63

Adsav2

Address saved when call.

MLX90308CCC

Programmable Sensor Interface

MLX90308CCC Programmable Sensor Interface

Page 22

Rev 2.2 23/Oct/01

Prototyping

Melexis offers an MLX90308 evaluation kit which
contains an evaluation circuit board, serial interface
cable, and software diskette. The circuit board
provides the necessary circuitry for all three
applications circuits shown on the next page. Also
included in the circuit board is level shifting and glue
logic necessary for RS-232 communications.

The board has a socket with a single MLX90308
installed, and direct access to the pins of the IC.
The user can easily attach bridge sensor to the
board for in-system evaluation. The serial interface
cable connects the evaluation board directly to a
PC's serial port for in-system calibration.

The software runs in the familiar Windows platform
and allows for programming and evaluation of all
compensation parameters within the EEPROM.

Figure 8. MLX90308 Evaluation Kit with MLX Software

MLX90308CCC

Programmable Sensor Interface

MLX90308CCC Programmable Sensor Interface

Page 24

Rev 2.2 23/Oct/01

IO1

IO2

TSTB

FLT

OFC

VBN

VBP

TMP

COMS

GND

CMN

CMO

VMO

VDD1

FET

VDD

MLX90308CCC

External FET

for Regulation

Pressure
Sensor

Oil

Pressure

(psi)

Communication

GND

Signal Out

V
+

Programmable Oil Pressure Gauge

This application example illustrates a fundamental

application of the MLX90308 and a bridge type

pressure sensor element. In this application, the

MLX90308 uses an external FET as a pass transistor to

regulate the voltage to the sensor and the analog portion

of the IC. This is known as Absolute Voltage Mode, where

voltage to the sensor and analog circuit is regulated independent

of the supply voltage. The MLX90308 can be operated in Ratiometric

Voltage Mode, in which the output (VMO) is tied to an A/D converter

sharing the same supply and ground reference. A third wiring option is

Current Mode, which allows the user a 4 to 20 milliampere current range to use as a
2-wire analog sensor.

Communications

Signal Out

GND

V+

Figure 10. Application Example

Figure 10a. Programmable Oil Pressure Gauge

Figure 10b. Programmable Oil Pressure Gauge Electrical Connections

MLX902xx Name of Sensor

Rev Y.X

22/Aug/98

Page 25

MLX90308CCC

Programmable Sensor Interface

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Rev 2.2 23/Oct/01

Pressure

100%

Voltage (in mV)

170

140

-40

Pressure

100%

Voltage (V

)

140

-40

Figure 11b. Conditioned Sensor
Output

Figures 11a and 11b above illustrate the
performance of an unconditioned sensor output and
a conditioned sensor output versus stimulus
(pressure) and temperature. It can be seen that
Figure 11a has a range of only 170 mV (maximum
range with a 5V supply) and has a non-linear
response over a 0-100 psi range. The sensitivity of
the unconditioned output will also drift over
temperature, as illustrated by the three slopes. The
MLX90308 corrects these errors and amplifies the
output to a more usable voltage range as shown in
Figure 11b.

Figure 11. Error Compensation

Table 14. Glossary of Terms

A/D

analog to digital conversion

ADC

analog to digital converter

ASCII

American Standard Code for Information

Interchange

ASIC

application specific integrated circuit

current mode

CMN

current mode negative (supply connection)

CMO

current mode output

COMS

communication, serial

carriage return

CSGN

coarse gain

CSOF

coarse offset

current / voltage mode select bit

DAC

digital to analog converter

DACFnew

filtered DAC value, new

DACFold

filtered DAC value, old

DARDIS

DAC resistor disable

decibel

DOGMO

digital mode

EEPROM

electrically erasable programmable read only

memory

EOC

end of conversion flag bit

ESD

electrostatic discharge

ETMI

timer interrupt enable

ETPI

enable temperature interrupt

FET

field effect transistor

fixed gain

FLT

filter pin

GNO

gain and offset adjusted digitized signal

GNOF

gain, offset

GNTP

temperature gain / offset coarse adjustment

hardware / software limit

I/O

input / output

IFIX

fixed current output value

IINV

input signal invert command bit

ILIM

current limit

kHz

kilohertz, 1000 Hz

LSB

least significant bit

milliamperes, 0.001 amps

MODSEL

mode select

millisecond, 0.001 second

MSB

most significant bit

MUX

multiplexer

millivolts, 0.001 Volts

nanofarads, 1 X 10

-9

farads

OFC

offset control

personal computer, IBM clone

picofarad, 1 X 10

-12

farads

PLL

phase locked loop

POR

power on reset

RAM

random access memory

RISC

reduced instruction set computer

ROM

read only memory

RS-232

industry std. serial communications protocol

receive

SAR

successive approximation register

STC

start A/D conversion

Tdiff

temperature difference

Text

temperature, external

TMI

timer Interrupt

TMP

temperature signal

TPI

temperature interrupt

Tref

temperature reference

TSTB

test mode pin

transmit

UART

universal asynchronous receiver / transmitter

VBN

bridge, positive, input

VBP

bridge, negative, input

supply voltage

voltage mode

VMGN

voltage mode gain

VMO

voltage mode output

WCB

warn / cold boot

Figure 11a. Raw Sensor Output
(measured between VPB and VBN)

Электронный компонент: MLX90308CCC