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PDF MAX1457 Data sheet ( Hoja de datos )
| Número de pieza | MAX1457 | |
| Descripción | 0.1%-Accurate Signal Conditioner for Piezoresistive Sensor Compensation | |
| Fabricantes | Maxim Integrated | |
| Logotipo |  |
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19-1342; Rev 1; 8/98
EVAALVUAAILTAIOBNLEKIT
0.1%-Accurate Signal Conditioner
for Piezoresistive Sensor Compensation
________________General Description
The MAX1457 is a highly integrated analog-sensor sig-
nal processor optimized for piezoresistive sensor cali-
bration and compensation. It includes a programmable
current source for sensor excitation, a 3-bit program-
mable-gain amplifier (PGA), a 12-bit ADC, five 16-bit
DACs, and an uncommitted op amp. Achieving a total
error factor within 0.1% of the sensor’s repeatability
errors, the MAX1457 compensates offset, full-span out-
put (FSO), offset TC, FSO TC, and full-span output non-
linearity of silicon piezoresistive sensors.
The MAX1457 calibrates and compensates first-order
temperature errors by adjusting the offset and span of
the input signal via digital-to-analog converters (DACs),
thereby eliminating quantization noise. If needed, resid-
ual higher-order errors are then compensated using lin-
ear interpolation of the first-order coefficients stored in
a look-up table (in external EEPROM).
The MAX1457 integrates 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 external EEPROM) of calibration and compensation
coefficients determined from transducer pretest data.
• Final Test: Verification of transducer calibration and
compensation, without removal from a pretest socket.
Analog outputs are provided for both pressure and tem-
perature. A general-purpose, uncommitted op amp is also
included on-chip to increase the overall circuit gain, or to
facilitate the implementation of a 2-wire, 4–20mA transmit-
ter. The serial interface is compatible with MicroWire™
and SPI™, and directly connects to an external EEPROM.
Additionally, built-in testability features of the MAX1457
facilitate manufacturing and calibration of multiple sensor
modules, thus lowering manufacturing cost.
Although optimized for use with piezoresistive sensors,
the MAX1457 may also be used with other resistive
sensor types (i.e., accelerometers and strain gauges)
with the addition of a few external components.
_______________________Customization
Maxim can customize the MAX1457 for unique require-
ments. With a dedicated cell library of more than 90
sensor-specific functional blocks, Maxim can quickly pro-
vide customized MAX1457 solutions. Contact Maxim for
additional information.
Rail-to-Rail is a registered trademark of Nippon Motorola, Ltd.
SPI is a trademark of Motorola, Inc.
MicroWire is a trademark of National Semiconductor Corp.
____________________________Features
o High Accuracy (within ±0.1% of sensor’s
repeatable errors)
o Compensates Offset, Offset TC, FSO, FSO TC,
Temperature/Pressure Nonlinearity
o Rail-to-Rail® Analog Output for Calibrated,
Temperature-Compensated Pressure
Measurements
o Programmable Sensor Excitation Current
o SPI/MicroWire-Compatible Serial Interface
o Fast Signal-Path Settling Time (<1ms)
o Accepts Sensor Outputs from 5mV/V to 30mV/V
o Pin-Compatible with MCA7707
_______________Ordering Information
PART
TEMP. RANGE PIN-PACKAGE
MAX1457CWI
0°C to +70°C
28 Wide SO
MAX1457CCJ
0°C to +70°C
32 TQFP
MAX1457C/D
0°C to +70°C
Dice*
Ordering Information continued at end of data sheet.
Note: Contact the factory for customized solutions.
*Dice are tested at TA = +25°C.
Pin Configurations appear at end of data sheet.
Functional Diagram
ISRC
BDRIVE
INP
INM
AGND
MCS
ECS
ECLK
EDI
EDO
LINDACREF
AMP+
AMP-
VDD
VDD BIAS
GENERATOR
MAX1457
OSCILLATOR
PGA
VDD
VSS
12-BIT ADC
SERIAL
EEPROM
INTERFACE
VDD
A=1
A=1
VBDRIVE A = 1
VSS
NBIAS
FADJ
FOUT
VOUT
LINDAC
FSOTCDAC
OTCDAC
OFSTDAC
FSODAC
LINOUT
FSOTCOUT
VBBUF
AMPOUT
________________________________________________________________ Maxim Integrated Products 1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 408-737-7600 ext. 3468.
1 page  
0.1%-Accurate Signal Conditioner
for Piezoresistive Sensor Compensation
_______________Detailed Description
The MAX1457 provides an analog amplification path for
the sensor signal and a digital path for calibration and
temperature correction. Calibration and correction are
achieved by varying the offset and gain of a program-
mable-gain amplifier (PGA) and by varying the sensor
bridge current. The PGA utilizes a switched-capacitor
CMOS technology, with an input-referred offset trim-
ming range of ±100mV (20mV/V) and an approximate
3µV (input referred, at minimum gain of 54V/V) resolu-
tion (16 bits). The PGA provides eight gain values from
54V/V to 306V/V. The bridge current source is program-
mable from 0.1mA to 2mA, with a 15nA step size.
The MAX1457 uses five 16-bit DACs with calibration
coefficients stored in a low-cost external EEPROM. This
memory (an external 4096-bit EEPROM) contains the
following calibration coefficients as 16-bit words:
• FSO (full-span output)
• FSO TC (including nonlinearities)
• Offset
• Offset TC (including nonlinearities)
• Pressure nonlinearity
Figure 1 shows a typical pressure-sensor output and
defines the offset, full-scale, and full-span output values
as a function of voltage.
Offset Correction
Initial offset calibration is accomplished by reading a
16-bit word (coefficient) from the EEPROM and writing it
to the OFFSET DAC. The resulting voltage (OFSTDAC)
is fed into a summing junction at the PGA output for
compensating the sensor offset with a resolution of
±0.2mV (±0.005% FSO).
FULL-SPAN OUTPUT (FSO)
FULL-SCALE (FS)
OFFSET
PRESSURE
Figure 1. Typical Pressure-Sensor Output
VDD
RSTC
IBR
BDRIVE
VBR
VBR
T
TO/FROM
EXTERNAL EEPROM
ECLK EDO
ECS EDI
TEMPERATURE-
DEPENDENT VOLTAGE
DAC REFERENCE VOLTAGE
16
EEPROM
INTERFACE
FSO TC
DAC
12
ADC
16
OFFSET TC
OUTPUT
Σ A=1
PGA
Figure 2. Simplified Diagram of Temperature Error Correction
_______________________________________________________________________________________ 5
5 Page 
0.1%-Accurate Signal Conditioner
for Piezoresistive Sensor Compensation
Table 1. MAX1457 Sensor Calibration and Compensation
Typical Uncompensated Input (Sensor)
Offset . . . . . . . . . . . . . . . . . . . . . . . . . .±100% FSO
FSO . . . . . . . . . . . . . . . . . . . . . .20mV/V to 30mV/V
Offset TC . . . . . . . . . . . . . . . . . . . . . . . . .20% FSO
Offset TC Nonlinearity . . . . . . . . . . . . . . . .4% FSO
FSO TC . . . . . . . . . . . . . . . . . . . . . . . . . .-20% FSO
FSO TC Nonlinearity . . . . . . . . . . . . . . . . . .5% FSO
Typical Compensated Transducer Output
Temperature Range . . . . . . . . . . .-40°C to +125°C
VOUT . . . . . . . . . . . . . . . .ratiometric to VDD at 5.0V
Offset at +25°C . . . . . . . . . . . . . . .0.500V ± 200µV
FSO at +25°C . . . . . . . . . . . . . . . . .4.000V ±200µV
Offset Accuracy Over
Temperature Range . . . . . . . . . .±4mV (0.1% FSO)
FSO Accuracy Over
Temperature Range . . . . . . . . ..±4mV (0.1% FSO)
UNCOMPENSATED RAW SENSOR OUTPUT
160
TA = +25°C
17mV ≤ VOUT ≤ 73mV
120
80
40
0
0 20 40 60 80 100
PRESSURE (kPa)
UNCOMPENSATED SENSOR TEMPERATURE ERROR
30
20
OFFSET
10
0
FSO
-10
-20
-50
0 50 100
TEMPERATURE (°C)
150
COMPENSATED TRANSDUCER
5
TA = +25°C
0.5V ≤ VOUT ≤ 4.5V
4
3
2
1
0
0 20 40 60 80 100
PRESSURE (kPa)
COMPENSATED TRANSDUCER ERROR
0.15
0.10
0.05
OFFSET
0
-0.05
FSO
-0.10
-0.15
-50
0 50 100
TEMPERATURE (°C)
150
Figure 8. Comparison of an Uncompensated Sensor (left) and a Compensated Transducer (right)
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet MAX1457.PDF ] | |
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