19-1619; Rev 0; 1/00
KIT
ATION
EVALU
BLE
AVAILA
2-Wire, 4–20mA
Smart Signal Conditioner
General Description
Features
o
Highly Integrated Sensor Signal Conditioner for
2-Wire, 4–20mA 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
MAX1459
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.
For custom versions of the MAX1459, see the Customization
section at end of data sheet.
Ordering Information
PART
MAX1459CAP
MAX1459C/D
TEMP. RANGE
0°C to +70°C
0°C to +70°C
PIN-PACKAGE
20 SSOP
Dice*
MAX1459AAP
-40°C to +125°C
20 SSOP
*Dice
are tested at T
A
= +25°C, DC parameters only.
Functional Diagram appears at end of data sheet.
Pin Configuration
TOP VIEW
SCLK 1
CS 2
DIO 3
WE 4
FSOTC 5
AMP+ 6
AMP- 7
AMPOUT 8
TEMPIN 9
ISRC 10
20 V
DD
19 NBIAS
18 CK50
MAX1459
17 TEMP2
16 TEMP1
15 INM
14 INP
13 BDRIVE
12 V
SS
11 OUT
________________________Applications
4–20mA Transmitters
Piezoresistive Pressure and Acceleration
Industrial Pressure Sensors
Load Cells/Wheatstone Bridges
Strain Gauges
Temperature Sensors
SSOP
1
________________________________________________________________
Maxim Integrated Products
For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
2-Wire, 4–20mA
Smart Signal Conditioner
MAX1459
ABSOLUTE MAXIMUM RATINGS
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
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.
ELECTRICAL CHARACTERISTICS
(V
DD
= +5V, V
SS
= 0, T
A
= +25°C, unless otherwise noted.)
PARAMETER
GENERAL CHARACTERISTICS
Supply Voltage
Supply Current
ANALOG INPUT
(PGA)
Input Impedance
Input-Referred Offset Tempco
Amplifier Gain Nonlinearity
Output Step Response
Common-Mode Rejection Ratio
Input-Referred Adjustable Offset
Range
Input-Referred Adjustable Full-
Span Output (FSO) Range
ANALOG OUTPUT
(PGA)
Differential Signal Gain Range
Minimum Differential Signal Gain
Differential Signal Gain Tempco
Output Voltage Swing
Output Current Range
Output Noise
CURRENT SOURCE
Bridge Current Range
Bridge Voltage Swing
Reference Input Voltage Range
(ISRC)
I
BDRIVE
V
BDRIVE
V
ISRC
I
BDRIVE
= 2mA
0.1
V
SS
+ 1.3
V
SS
+ 1.3
0.5
2.0
V
DD
- 1.3
V
DD
- 1.3
mA
V
V
Selectable in eight steps
T
A
= T
MIN
to T
MAX
T
A
= T
MIN
to T
MAX
No load
10kΩ load
V
OUT
= (V
SS
+ 0.25V) to (V
DD
- 0.25V)
DC to 10Hz (gain = 41,
source impedance = 5kΩ)
V
SS
+ 0.05
V
SS
+ 0.25
-0.45
(sink)
500
+36
+41 to +230
+41
±50
V
DD
- 0.05
V
DD
- 0.25
0.45
(source)
+44
V/V
V/V
ppm/°C
V
mA
µV
RMS
CMRR
63% of final value
From V
SS
to V
DD
At minimum gain (Note 4)
(Note 5)
R
IN
(Notes 2, 3)
1
±0.5
0.01
2
90
±150
+1 to +40
MΩ
µV/°C
%V
DD
ms
dB
mV
mV/V
V
DD
I
DD
R
NBIAS
= 402kΩ, V
DD
= 5.0V (Note 1)
4.5
5.0
2.0
5.5
2.5
V
mA
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
2
_______________________________________________________________________________________
2-Wire, 4–20mA
Smart Signal Conditioner
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= +5V, V
SS
= 0, T
A
= +25°C, unless otherwise noted.)
PARAMETER
DAC Resolution
Differential Nonlinearity
Offset DAC Bit Weight
Offset TC DAC Bit Weight
FSO DAC Bit Weight
FSOTC DAC Bit Weight
IRO DAC
DAC Resolution
DAC Bit Weight
FSOTC BUFFER
(FSOTC Pin)
Output Voltage Swing
Current Drive
INTERNAL RESISTORS
Current Source Reference
Resistor
FSO Trim Resistor
Temperature-Dependent
Resistor
AUXILIARY OP AMP
Input Common-Mode Range
Open-Loop Gain
Offset Voltage (as unity-gain
follower)
Output Swing
Output Current
CMR
A
V
V
IN
= V
DD
/2
No load
-30
V
SS
+ 0.05
±1
V
SS
60
30
V
DD -
0.05
V
DD
V
dB
mV
V
mA
R
ISRC
R
FTC
R
TEMP
100
100
100
kΩ
kΩ
kΩ
No load, V
B
= 5V
V
FSOTC
= 2.5V
0.2
-20
4.0
20
V
µA
Input referred, V
DD
= 5V (Note 6)
3
9
Bits
mV/bit
DNL
∆V
OUT
∆Code
∆V
OUT
∆Code
∆V
ISRC
∆Code
∆V
FSOT
∆Code
DAC reference = V
DD
= 5.0V
DAC reference = V
BDRIVE
= 2.5V
DAC reference = V
DD
= 5.0V
DAC reference = V
BDRIVE
= 2.5V
SYMBOL
CONDITIONS
MIN
TYP
12
±1.5
2.8
1.4
1.22
0.6
MAX
UNITS
Bits
LSB
mV/bit
mV/bit
mV/bit
mV/bit
DIGITAL-TO-ANALOG CONVERTERS
MAX1459
3
_______________________________________________________________________________________
2-Wire, 4–20mA
Smart Signal Conditioner
MAX1459
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= +5V, V
SS
= 0, T
A
= +25°C, unless otherwise noted.)
PARAMETER
DIGITAL PINS
High-Level Input Voltage
Low-Level Input Voltage
Input Hysteresis
High-Level Output Voltage
Low-Level Output Voltage
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
V
OH
V
OL
I
SOURCE
= 1mA
I
SINK
= 2mA
4
0.5
V
IH
V
IL
2
0.75 x V
DD
0.25 x V
DD
V
V
V
V
V
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Excludes the sensor or load current.
All electronics temperature errors are compensated together with sensor errors.
The sensor and the MAX1459 must always be at the same temperature during calibration and use.
This is the maximum allowable sensor offset.
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
.
__________________________________________Typical Operating Characteristics
(V
DD
= +5V, V
SS
= 0, T
A
= +25°C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
MAX1459 toc01
R
TEMP
vs. TEMPERATURE
MAX1459 toc02
V
OUT
vs. TEMPERATURE
4.5
4.0
3.5
V
OUT
(V)
3.0
2.5
2.0
1.5
1.0
0.5
V
OUT
= 2.47V AT +25°C
V
IN
= 0
V
OUT
= 2.5V AT +25°C
V
IN
= 56.5mV
MAX1459 toc03
2.5
V
OUT
= 2.47V AT +25°C
2.0
SUPPLY CURRENT (mA)
200
180
160
140
R
TEMP
(Ω)
5.0
1.5
120
100
80
60
1.0
0.5
40
20
0
-40
-20
0
20
40
60
80
100 120
0
-40
-20
0
20
40
60
80
100 120
0
-40
-20
0
20
40
60
80
100 120
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
4
_______________________________________________________________________________________
2-Wire, 4–20mA
Smart Signal Conditioner
Pin Description
PIN
1
2
3
NAME
SCLK
CS
DIO
FUNCTION
Data Clock Input. Used only during programming/testing. Internally pulled to V
SS
with a 1MΩ (typical) resistor.
Data is clocked in on the rising edge of the clock. Recommended SCLK frequency is below 50kHz.
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 1MΩ (typical) resistor. Leave unconnected for normal operation.
Data Input/Output. Used only during programming/testing. Internally pulled to V
SS
with a 1MΩ (typical)
resistor. High impedance when CS is low.
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 1MΩ (typ) resistor. See the
Chip-Select (CS)
and Write-Enable (WE)
section.
Buffered Full-Span Output Temperature Coefficient DAC Output. An internal 100kΩ 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
.
Auxiliary Op Amp Positive Input
Auxiliary Op Amp Negative Input
Auxiliary Op Amp Output
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.
Current Source Reference. An internal 100kΩ 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
.
Output Voltage. OUT is a Rail-to-Rail® output that can drive resistive loads down to 10kΩ and capacitive
loads up to 0.1µF.
Negative Power Supply
Sensor Excitation Current Output. The current source that drives the bridge.
Positive Sensor Input. Input impedance is typically 1MΩ. Rail-to-rail input range.
Negative Sensor Input. Input impedance is typically 1MΩ. Rail-to-rail input range.
Temperature Sensor Terminal 1
Temperature Sensor Terminal 2. R
TEMP
is a 100kΩ temperature-dependent resistor with 4600ppm/°C
tempco.
Clock Output, nominally 50kHz
Chip Current Bias Source. Connect an external 402kΩ ±1% resistor between V
DD
and NBIAS.
Positive Power-Supply Input. Connect a 0.1µF capacitor from V
DD
to V
SS
.
MAX1459
4
WE
5
6
7
8
9
FSOTC
AMP+
AMP-
AMPOUT
TEMPIN
10
11
12
13
14
15
16
17
18
19
20
ISRC
OUT
V
SS
BDRIVE
INP
INM
TEMP1
TEMP2
CK50
NBIAS
V
DD
Rail-to-Rail is a registered trademark of Nippon Motorola, Ltd.
_______________________________________________________________________________________
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