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General Description
The MAX1459 highly integrated analog-sensor signal
conditioner is optimized for piezoresistive sensor calibra-
tion and compensation with minimal external compo-
nents. It includes a programmable current source for
sensor excitation, a 3-bit programmable-gain amplifier
(PGA), a 128-bit internal EEPROM, and four 12-bit DACs.
Achieving a total error factor within 1% of the sensor's
repeatability errors, the MAX1459 compensates offset,
offset temperature coefficient (offset TC), full-span output
(FSO), FSO temperature coefficient (FSOTC), and FSO
nonlinearity of silicon piezoresistive sensors.
The MAX1459 calibrates and compensates first-order
temperature errors by adjusting the offset and span of
the input signal through digital-to-analog converters
(DACs), thereby eliminating quantization noise.
The MAX1459 allows temperature compensation via the
external sensor, an internal temperature-dependent
resistor, or a dedicated external temperature transduc-
er. Accuracies better than 0.5% can be achieved with
low-cost external temperature sensors (i.e., silicon tran-
sistor), depending on sensor choice.
Built-in testability features on the MAX1459 result in the
integration of three traditional sensor-manufacturing
operations into one automated process:
· Pretest: Data acquisition of sensor performance
under the control of a host test computer.
· Calibration and compensation: Computation and
storage (in an internal EEPROM) of calibration and
compensation coefficients computed by the test
computer and downloaded to the MAX1459.
· Final test operation: Verification of transducer cali-
bration and compensation without removal from the
pretest socket.
Although optimized for use with piezoresistive sensors,
the MAX1459 may also be used with other resistive
sensors (i.e., accelerometers and strain gauges) with
some additional external components.
________________________Applications
420mA Transmitters
Piezoresistive Pressure and Acceleration
Industrial Pressure Sensors
Load Cells/Wheatstone Bridges
Strain Gauges
Temperature Sensors
Features
o Highly Integrated Sensor Signal Conditioner for
2-Wire, 420mA Transmitters
o Sensor Errors Trimmed Using Correction
Coefficients Stored in Internal EEPROM--
Eliminates the Need for Laser Trimming and
Potentiometers
o Compensates Offset, Offset TC, FSO, FSOTC,
FSO Linearity
o Programmable Current Source (0.1mA to 2.0mA)
for Sensor Excitation
o Fast Signal-Path Settling Time (1ms)
o Accepts Sensor Outputs from +1mV/V to +40mV/V
o Fully Analog Signal Path
o Internal or External Temperature Reference
Compensation
o Automated Pilot Production (Calibration/
Compensation) System Available
o Write Protection for EEPROM Data Security
Pin Configuration
Ordering Information
MAX1459
2-Wire, 420mA
Smart Signal Conditioner
________________________________________________________________ Maxim Integrated Products
1
20
19
18
17
16
15
14
13
1
2
3
4
5
6
7
8
SCLK
V
DD
NBIAS
CK50
TEMP2
TEMP1
INM
INP
BDRIVE
TOP VIEW
MAX1459
SSOP
CS
DIO
AMP+
WE
FSOTC
AMP-
AMPOUT
12
11
9
10
V
SS
OUT
TEMPIN
ISRC
19-1619; Rev 0; 1/00
*Dice are tested at T
A
= +25°C, DC parameters only.
Functional Diagram appears at end of data sheet.
EVALUATION KIT
AVAILABLE
20 SSOP
Dice*
20 SSOP
PIN-PACKAGE
TEMP. RANGE
0°C to +70°C
0°C to +70°C
-40°C to +125°C
MAX1459AAP
MAX1459C/D
MAX1459CAP
PART
For custom versions of the MAX1459, see the Customization
section at end of data sheet.
MAX1459
2-Wire, 420mA
Smart Signal Conditioner
2
_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Supply Voltage, V
DD
to V
SS
......................................-0.3V to +6V
All Other Pins ...................................(V
SS
- 0.3V) to (V
DD
+ 0.3V)
Short-Circuit Duration, FSOTC, OUT, BDRIVE ...........Continuous
Continuous Power Dissipation (T
A
= +70°C)
20-Pin SSOP (derate 8.00mW/°C above +70°C) ..........640mW
Operating Temperature Ranges
MAX1459CAP ......................................................0°C to +70°C
MAX1459AAP .................................................-40°C to +125°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
ELECTRICAL CHARACTERISTICS
(V
DD
= +5V, V
SS
= 0, T
A
= +25°C, unless otherwise noted.)
PARAMETER
SYMBOL
MIN
TYP
MAX
UNITS
Amplifier Gain Nonlinearity
0.01
%V
DD
Input-Referred Offset Tempco
±0.5
µV/°C
Input Impedance
R
IN
1
M
Output Step Response
2
ms
Common-Mode Rejection Ratio
CMRR
90
dB
Input-Referred Adjustable Offset
Range
±150
mV
Supply Voltage
V
DD
4.5
5.0
5.5
V
Supply Current
I
DD
2.0
2.5
mA
Input-Referred Adjustable Full-
Span Output (FSO) Range
+1 to +40
mV/V
Differential Signal Gain Range
+41 to +230
V/V
Minimum Differential Signal Gain
+36
+41
+44
V/V
Differential Signal Gain Tempco
±50
ppm/°C
Output Current Range
-0.45 0.45
(sink)
(source)
mA
Output Noise
500
µV
RMS
CONDITIONS
(Note 5)
(Notes 2, 3)
63% of final value
Selectable in eight steps
T
A
= T
MIN
to T
MAX
From V
SS
to V
DD
At minimum gain (Note 4)
T
A
= T
MIN
to T
MAX
V
OUT
= (V
SS
+ 0.25V) to (V
DD
- 0.25V)
DC to 10Hz (gain = 41,
source impedance = 5k
)
R
NBIAS
= 402k
, V
DD
= 5.0V (Note 1)
Output Voltage Swing
V
SS
+ 0.05
V
DD
- 0.05
V
No load
V
SS
+ 0.25
V
DD
- 0.25
10k
load
GENERAL CHARACTERISTICS
ANALOG INPUT (PGA)
ANALOG OUTPUT (PGA)
Bridge Current Range
I
BDRIVE
0.1
0.5
2.0
mA
Bridge Voltage Swing
V
BDRIVE
V
SS
+ 1.3
V
DD
- 1.3
V
I
BDRIVE
= 2mA
Reference Input Voltage Range
(ISRC)
V
ISRC
V
SS
+ 1.3
V
DD
- 1.3
V
CURRENT SOURCE
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= +5V, V
SS
= 0, T
A
= +25°C, unless otherwise noted.)
MAX1459
2-Wire, 420mA
Smart Signal Conditioner
_______________________________________________________________________________________
3
FSO DAC Bit Weight
V
ISRC
Code
1.22
mV/bit
FSOTC DAC Bit Weight
V
FSOT
Code
0.6
mV/bit
DAC reference = V
DD
= 5.0V
DAC reference = V
BDRIVE
= 2.5V
Offset DAC Bit Weight
V
OUT
Code
2.8
mV/bit
Offset TC DAC Bit Weight
V
OUT
Code
1.4
mV/bit
DAC reference = V
DD
= 5.0V
DAC reference = V
BDRIVE
= 2.5V
DAC Resolution
12
Bits
Differential Nonlinearity
DNL
±1.5
LSB
PARAMETER
SYMBOL
MIN
TYP
MAX
UNITS
DAC Bit Weight
9
mV/bit
DAC Resolution
3
Bits
Output Voltage Swing
0.2
4.0
V
Current Drive
-20
20
µA
Current Source Reference
Resistor
R
ISRC
100
k
FSO Trim Resistor
R
FTC
100
k
Temperature-Dependent
Resistor
R
TEMP
100
k
CONDITIONS
Input referred, V
DD
= 5V (Note 6)
No load, V
B
= 5V
V
FSOTC
= 2.5V
Input Common-Mode Range
CMR
V
SS
V
DD
V
Open-Loop Gain
A
V
60
dB
Offset Voltage (as unity-gain
follower)
-30
30
mV
V
IN
= V
DD
/2
Output Swing
V
SS
+ 0.05
V
DD -
0.05
V
No load
Output Current
±1
mA
DIGITAL-TO-ANALOG CONVERTERS
IRO DAC
FSOTC BUFFER (FSOTC Pin)
INTERNAL RESISTORS
AUXILIARY OP AMP
MAX1459
2-Wire, 420mA
Smart Signal Conditioner
4
_______________________________________________________________________________________
__________________________________________Typical Operating Characteristics
(V
DD
= +5V, V
SS
= 0, T
A
= +25°C, unless otherwise noted.)
0
0.5
1.0
1.5
2.0
2.5
-40
40
60
0
20
-20
80
100 120
SUPPLY CURRENT vs. TEMPERATURE
MAX1459 toc01
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
V
OUT
= 2.47V AT +25°C
-40
40
60
0
20
-20
80
100 120
R
TEMP
vs. TEMPERATURE
MAX1459 toc02
TEMPERATURE (°C)
R
TEMP
(
)
0
60
40
20
80
100
120
140
160
180
200
-40
40
60
0
20
-20
80
100 120
V
OUT
vs. TEMPERATURE
MAX1459 toc03
TEMPERATURE (°C)
V
OUT
(V)
0
1.5
1.0
0.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
V
OUT
= 2.5V AT +25°C
V
IN
= 56.5mV
V
OUT
= 2.47V AT +25°C
V
IN
= 0
Note 1: Excludes the sensor or load current.
Note 2: All electronics temperature errors are compensated together with sensor errors.
Note 3: The sensor and the MAX1459 must always be at the same temperature during calibration and use.
Note 4: This is the maximum allowable sensor offset.
Note 5: This is the sensor's sensitivity normalized to its drive voltage, assuming a desired full-span output of 4V and a bridge
voltage of 2.5V. Sensors smaller than +10mV/V require an auxiliary op amp.
Note 6: Bit weight is ratiometric to V
DD
.
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= +5V, V
SS
= 0, T
A
= +25°C, unless otherwise noted.)
I
SINK
= 2mA
V
0.5
V
OL
Low-Level Output Voltage
I
SOURCE
= 1mA
V
4
V
OH
High-Level Output Voltage
V
2
Input Hysteresis
V
0.25 x V
DD
V
IL
Low-Level Input Voltage
V
0.75 x V
DD
V
IH
High-Level Input Voltage
CONDITIONS
UNITS
MIN
TYP
MAX
SYMBOL
PARAMETER
DIGITAL PINS
MAX1459
2-Wire, 420mA
Smart Signal Conditioner
_______________________________________________________________________________________
5
Temperature Sensor Terminal 1
TEMP1
16
Temperature Sensor Terminal 2. R
TEMP
is a 100k
temperature-dependent resistor with 4600ppm/°C
tempco.
TEMP2
17
Output Voltage. OUT is a Rail-to-Rail® output that can drive resistive loads down to 10k
and capacitive
loads up to 0.1µF.
OUT
11
Negative Power Supply
V
SS
12
Sensor Excitation Current Output. The current source that drives the bridge.
BDRIVE
13
Positive Sensor Input. Input impedance is typically 1M
. Rail-to-rail input range.
INP
14
Negative Sensor Input. Input impedance is typically 1M
. Rail-to-rail input range.
INM
15
Auxiliary Op Amp Negative Input
AMP-
7
Auxiliary Op Amp Output
AMPOUT
8
Input pin for an External Temperature-Dependent Reference Voltage for FSOTC DAC and OTC DAC. In the
default mode, the MAX1459 uses the temperature-dependent bridge drive voltage as the FSOTC DAC and
OTC DAC reference.
TEMPIN
9
Current Source Reference. An internal 100k
resistor (R
ISRC
) connects ISRC to V
SS
(see Functional
Diagram). Optionally, external resistors can be used in place of or in parallel with R
FTC
and R
ISRC
.
ISRC
10
Auxiliary Op Amp Positive Input
AMP+
6
Buffered Full-Span Output Temperature Coefficient DAC Output. An internal 100k
resistor (R
FTC
) con-
nects FSOTC to ISRC (see Functional Diagram). Optionally, external resistors can be used in place of or in
parallel with R
FTC
and R
ISC
.
FSOTC
5
Write Enable, Dual-Function Input Pin. Used to enable EEPROM erase/write operations. Also used to set
the DAC refresh-rate mode. Internally pulled to V
DD
with a 1M
(typ) resistor. See the Chip-Select (CS)
and Write-Enable (WE) section.
WE
4
Data Input/Output. Used only during programming/testing. Internally pulled to V
SS
with a 1M
(typical)
resistor. High impedance when CS is low.
DIO
3
Positive Power-Supply Input. Connect a 0.1µF capacitor from V
DD
to V
SS
.
V
DD
20
Clock Output, nominally 50kHz
CK50
18
Chip Current Bias Source. Connect an external 402k
±1% resistor between V
DD
and NBIAS.
NBIAS
19
Pin Description
1
Chip-Select Input. The MAX1459 is selected when this pin is high. When low, OUT and DIO become high
impedance. Internally pulled to V
DD
with a 1M
(typical) resistor. Leave unconnected for normal operation.
CS
2
Data Clock Input. Used only during programming/testing. Internally pulled to V
SS
with a 1M
(typical) resistor.
Data is clocked in on the rising edge of the clock. Recommended SCLK frequency is below 50kHz.
SCLK
PIN
FUNCTION
NAME
Rail-to-Rail is a registered trademark of Nippon Motorola, Ltd.
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