MAX1452CAE-T中文资料
MAX1452
Low-Cost Precision Sensor
Signal Conditioner
________________________________________________________________Maxim Integrated Products 1
General Description
The MAX1452 is a highly integrated analog-sensor sig-nal processor optimized for industrial and process con-trol applications utilizing resistive element sensors.The MAX1452 provides amplification, calibration, and temperature compensation that enables an overall per-formance approaching the inherent repeatability of the sensor. The fully analog signal path introduces no quantization noise in the output signal while enabling digitally controlled trimming with the integrated 16-bit DACs. Offset and span are calibrated using 16-bit DACs, allowing sensor products to be truly inter-changeable.
The MAX1452 architecture includes a programmable sensor excitation, a 16-step programmable-gain ampli-fier (PGA), a 768-byte (6144 bits) internal EEPROM,four 16-bit DACs, an uncommitted op amp, and an on-chip temperature sensor. In addition to offset and span compensation. The MAX1452 provides a unique tem-perature compensation strategy for offset TC and FSOTC that was developed to provide a remarkable degree of flexibility while minimizing testing costs.The MAX1452 is packaged for the commercial, industri-al, and automotive temperature ranges in 16-pin SSOP packages.
Customization
Maxim can customize the MAX1452 for high-volume dedicated applications. Using our dedicated cell library of more than 2000 sensor-specific functional blocks,Maxim can quickly provide a modified MAX1452 solu-tion. Contact Maxim for further information.
Applications
Pressure Sensors
Transducers and Transmitters Strain Gauges
Pressure Calibrators and Controllers Resistive Elements Sensors Accelerometers Humidity Sensors
Outputs Supported
4–20mA
0 to +5V (Rail-to-Rail ?)+0.5V to +4.5V Ratiometric +2.5V to ±2.5V
Features
o Provides Amplification, Calibration, and Temperature Compensation o Accommodates Sensor Output Sensitivities from 1mV/V to 40mV/V o Single Pin Digital Programming
o No External Trim Components Required o 16-Bit Offset and Span Calibration Resolution o Fully Analog Signal Path
o On-Chip Lookup Table Supports Multipoint Calibration Temperature Correction o Supports Both Current and Voltage Bridge Excitation o Fast 3.2kHz Frequency Response o On-Chip Uncommitted Op Amp
o Secure-Lock?Prevents Data Corruption o Low 2mA Current Consumption
Rail-to-Rail is a trademark of Nippon Motorola Ltd.
Secure-Lock is a trademark of Maxim Integrated Products.
Pin Configuration
Ordering Information
*Dice are tested at T A = +25°C, DC parameters only.
A detailed block diagram appears at the end of data sheet.
For pricing, delivery, and ordering information,please contact Maxim/Dallas Direct!at 1-888-629-4642, or visit Maxim’s website at https://www.wendangku.net/doc/957053121.html,.
M A X 1452
Low-Cost Precision Sensor Signal Conditioner
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
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, +6V All Other Pins...................................(V SS - 0.3V) to (V DD + 0.3V)Short-Circuit Duration, FSOTC, OUT, BDR,
AMPOUT.................................................................Continuous Continuous Power Dissipation (T A = +70°C)
16-Pin SSOP (derate 8.00mW/°C above +70°C)..........640mW
Operating Temperature:
MAX1452CAE/MAX1452C/D ...............................0°C to +70°C MAX1452EAE ...................................................-40°C to +85°C MAX1452AAE.................................................-40°C to +125°C Junction Temperature......................................................+150°C Storage Temperature.........................................-65°C to +150°C Lead Temperature (soldering, 10s)................................+300°C
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ELECTRICAL CHARACTERISTICS (continued)
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Note 2:All electronics temperature errors are compensated together with sensors errors.
Note 3:The sensor and the MAX1452 must 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 volt-age of +2.5V.
Note 6:Bit weight is ratiometric to V DD .
Note 7:Programming of the EEPROM at room temperature is recommended.Note 8:Allow a minimum of 6ms elapsed time before sending any command.
ELECTRICAL CHARACTERISTICS (continued)
(V DD = +5V, V SS = 0, T A = +25°C, unless otherwise noted.)
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Typical Operating Characteristics
(V DD = +5V, T A = +25°C, unless otherwise noted.)
OFFSET DAC DNL
M A X 1452 t o c 01
DAC CODE
D N
L (m V )
30k
40k
10k
20k
50k
60k
70k
5.0
2.50
-2.5
-5.0
5.0
2.5
-2.5
-5.0
AMPLIFIER GAIN NONLINEARITY
INPUT VOLTAGE [INP-INM] (mV)
O U T P U T E R R O R F R O M S T R A I G H T L I N E (m V )
-500-252550
OUTPUT NOISE
M A X 1452 t o c 03
400μs/div
C = 4.7μF, R LOA
D = 1k ?
OUT 10mV/div
M A X 1452
Detailed Description
The MAX1452 provides amplification, calibration, and temperature compensation to enable an overall perfor-mance approaching the inherent repeatability of the sensor. The fully analog signal-path introduces no quantization noise in the output signal while enabling digitally controlled trimming with the integrated 16-bit DACs. Offset and span can be calibrated to within ±0.02% of span.
The MAX1452 architecture includes a programmable sensor excitation, a 16-step programmable-gain ampli-fier (PGA), a 768-byte (6144 bits) internal EEPROM, four 16-bit DACs, an uncommitted op amp, and an on-chip temperature sensor.The MAX1452 also provides a unique temperature compensation strategy for offset TC and FSOTC that was developed to provide a remarkable degree of flexibility while minimizing testing costs.
The customer can select from one to 114 temperature points to compensate their sensor. This allows the lati-tude to compensate a sensor with a simple first order linear correction or match an unusual temperature curve. Programming up to 114 independent 16-bit EEP-ROM locations corrects performance in 1.5°C tempera-ture increments over a range of -40°C to +125°C. For sensors that exhibit a characteristic temperature perfor-mance, a select number of calibration points can be used with a number of preset values that define the temperature curve. I n cases where the sensor is at a different temperature than the ASIC, the MAX1452 uses the sensor bridge itself to provide additional tempera-ture correction.
nication architecture and the ability to timeshare its activity with the sensor ’s output signal enables output sensing and calibration programming on a single line by parallel connecting OUT and DI O. The MAX1452provides a Secure-Lock feature that allows the cus-tomer to prevent modification of sensor coefficients and the 52-byte user definable EEPROM data after the sen-sor has been calibrated. The Secure-Lock feature also provides a hardware override to enable factory rework and recalibration by assertion of logic high on the UNLOCK pin.
The MAX1452 allows complete calibration and sensor verification to be performed at a single test station.Once calibration coefficients have been stored in the ASIC, the customer can choose to retest in order to ver-ify performance as part of a regular QA audit or to gen-erate final test data on individual sensors.
The MAX1452’s low current consumption and the inte-grated uncommitted op amp enables a 4–20mA output signal format in a sensor that is completely powered from a 2-wire current loop. Frequency response can be user-adjusted to values lower than the 3.2kHz band-width by using the uncommitted op amp and simple passive components.
The MAX1452 (Figure 1) provides an analog amplifica-tion path for the sensor signal. I t also uses an analog architecture for first-order temperature correction. A digitally controlled analog path is then used for nonlin-ear temperature correction. Calibration and correction is achieved by varying the offset and gain of a pro-grammable-gain-amplifier (PGA) and by varying the sensor bridge excitation current or voltage. The PGA
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utilizes a switched capacitor CMOS technology, with an input referred offset trimming range of more than ±150mV with an approximate 3μV resolution (16 bits).The PGA provides gain values from 39V/V to 240V/V in 16 steps.
The MAX1452 uses four 16-bit DACs with calibration coefficients stored by the user in an internal 768 x 8EEPROM (6144 bits). This memory contains the follow-ing information, as 16-bit wide words:?Configuration Register ?Offset Calibration Coefficient Table ?Offset Temperature Coefficient Register ?FSO (Full-Span Output) Calibration Table
?FSO Temperature Error Correction Coefficient Register
?
52 bytes (416 bits) uncommitted for customer pro-gramming of manufacturing data (e.g., serial num-ber and date)
Offset Correction
I nitial offset correction is accomplished at the input stage of the signal gain amplifiers by a coarse offset setting. Final offset correction occurs through the use of a temperature indexed lookup table with 176 16-bit entries. The on-chip temperature sensor provides a unique 16-bit offset trim value from the table with an indexing resolution of approximately 1.5°C from -40°C to +125°C. Every millisecond, the on-chip temperature sensor provides indexing into the offset lookup table in EEPROM and the resulting value transferred to the off-set DAC register. The resulting voltage is fed into a summing junction at the PGA output, compensating the sensor offset with a resolution of ±76μV (±0.0019%FSO). If the offset TC DAC is set to zero then the maxi-mum temperature error is equivalent to one degree of temperature drift of the sensor, given the Offset DAC has corrected the sensor at every 1.5°C. The tempera-ture indexing boundaries are outside of the specified Absolute Maximum R atings . The minimum indexing value is 00hex corresponding to approximately -69°C.All temperatures below this value will output the coeffi-cient value at index 00hex. The maximum indexing value is AFhex, which is the highest lookup table entry.All temperatures higher than approximately 184°C will output the highest lookup table index value. No index-ing wrap-around errors are produced.
FSO Correction
Two functional blocks control the FSO gain calibration.First, a coarse gain is set by digitally selecting the gain of the PGA. Second, FSO DAC sets the sensor bridge current or voltage with the digital input obtained from a temperature-indexed reference to the FSO lookup table in EEPROM. FSO correction occurs through the use of a temperature indexed lookup table with 176 16-bit entries. The on-chip temperature sensor provides a unique FSO trim from the table with an indexing resolu-tion approaching one 16-bit value at every 1.5°C from -40°C to +125°C. The temperature indexing boundaries are outside of the specified Absolute Maximum Ratings . The minimum indexing value is 00hex corre-sponding to approximately -69°C. All temperatures below this value will output the coefficient value at index 00hex. The maximum indexing value is AFhex,which is the highest lookup table entry. All tempera-tures higher than approximately 184°C will output the highest lookup table index value. No indexing wrap-around errors are produced.
Linear and Nonlinear Temperature
Compensation
Writing 16-bit calibration coefficients into the offset TC and FSOTC registers compensates first-order tempera-MAX1452
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Figure 1. Functional Diagram
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ture errors. The piezoresistive sensor is powered by a current source resulting in a temperature-dependent bridge voltage due to the sensor's temperature resis-tance coefficient (TCR). The reference inputs of the off-set TC DAC and FSOTC DAC are connected to the bridge voltage. The DAC output voltages will track the bridge voltage as it varies with temperature, and by varying the offset TC and FSOTC digital code a portion of the bridge voltage, which is temperature dependent,is used to compensate the first order temperature errors.
The internal feedback resistors (R ISRC and R STC ) for FSO temperature compensation are optimized to 75k ?for silicon piezoresistive sensors. However, since the required feedback resistor values are sensor depen-dent, external resistors may also be used. The internal resistors selection bit in the configuration register selects between internal and external feedback resis-tors.
To calculate the required offset TC and FSOTC com-pensation coefficients, two test-temperatures are need-ed. After taking at least two measurements at each temperature, calibration software (in a host computer)calculates the correction coefficients and writes them to the internal EEPROM.
With coefficients ranging from 0000hex to FFFFhex and a +5V reference, each DAC has a resolution of 76μV.Two of the DACs (offset TC and FSOTC) utilize the sen-sor bridge voltage as a reference. Since the sensor bridge voltage is approximately set to +2.5V the FSOTC and offset TC exhibit a step size of less than 38μV.
For high accuracy applications (errors less than 0.25%), the first-order offset and FSOTC should be compensated with the offset TC and FSOTC DACs, and the residual higher order terms with the lookup table.The offset and FSO compensation DACs provide unique compensation values for approximately 1.5°C of temperature change as the temperature indexes the address pointer through the coefficient lookup table.Changing the offset does not effect the FSO, however changing the FSO will affect the offset due to nature of the bridge. The temperature is measured on both the MAX1452 die and at the bridge sensor. I t is recom-mended to compensate the first-order temperature errors using the bridge sensor temperature.
Typical Ratiometric Operating Circuit
Ratiometric output configuration provides an output that is proportional to the power supply voltage. This output can then be applied to a ratiometric ADC to produce a digital value independent of supply voltage.Ratiometricity is an important consideration for battery-operated instruments, automotive, and some industrial applications.
The MAX1452 provides a high-performance ratiometric output with a minimum number of external components (Figure 2). These external components include the fol-lowing:
?One supply bypass capacitor.?One optional output EMI suppression capacitor.?
Two optional resistors, RISRC and RSTC, for special sensor bridge types.
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Figure 2. Basic Ratiometric Output Configuration
Typical Nonratiometric
Operating Circuit
(12VDC < VPWR < 40VDC)
Nonratiometric output configuration enables the sensor power to vary over a wide range. A high performance voltage reference, such as the MAX6105, is incorporat-ed in the circuit to provide a stable supply and refer-ence for MAX1452 operation. A typical example is shown in Figure 3. Nonratiometric operation is valuable when wide ranges of input voltage are to be expected and the system A/D or readout device does not enable ratiometric operation.
Typical 2-Wire, Loop Powered,
4–20mA Operating Circuit
Process Control systems benefit from a 4–20mA current loop output format for noise immunity, long cable runs,and 2-wire sensor operation. The loop voltages can range from 12VDC to 40VDC and are inherently nonra-tiometric. The low current consumption of the MAX1452allows it to operate from loop power with a simple 4–20mA drive circuit efficiently generated using the integrated uncommitted op amp (Figure 4).
Internal Calibration Registers (ICRs)
The MAX1452 has five 16-bit internal calibration regis-ters that are loaded from EEPROM, or loaded from the serial digital interface.
Data can be loaded into the internal calibration regis-ters under three different circumstances.
Normal Operation, Power-On Initialization Sequence ?The MAX1452 has been calibrated, the Secure-Lock byte is set (CL[7:0] = FFhex) and UNLOCK is low.?Power is applied to the device.
?The power-on reset functions have completed.?Registers CONFIG, OTCDAC, and FSOTCDAC are refreshed from EEPROM.
?
Registers ODAC, and FSODAC are refreshed from the temperature indexed EEPROM locations.Normal Operation, Continuous Refresh ?
The MAX1452 has been calibrated, the Secure-Lock byte has been set (CL[7:0] = FFhex) and UNLOCK is low.
?Power is applied to the device.
?The power-on reset functions have completed.?
The temperature index timer reaches a 1ms time period.
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Figure 3. Basic Nonratiometric Output Configuration
M A X 1452
?Registers CONFIG, OTCDAC, and FSOTCDAC are refreshed from EEPROM.
?
Registers ODAC and FSODAC are refreshed from the temperature indexed EEPROM locations.
Calibration Operation, Registers Updated by Serial Communications ?The MAX1452 has not had the Secure-Lock byte set (CL[7:0] = 00hex) or UNLOCK is high.?Power is applied to the device.
?The power-on reset functions have completed.?
The registers can then be loaded from the serial digital interface by use of serial commands. See the section on Serial I/O and Commands.
Internal EEPROM
The internal EEPROM is organized as a 768 by 8-bit memory. It is divided into 12 pages, with 64 bytes per page. Each page can be individually erased. The mem-ory structure is arranged as shown in Table 1. The look-up tables for ODAC and FSODAC are also shown, with the respective temp-index pointer. Note that the ODAC table occupies a continuous segment, from address 000hex to address 15Fhex, whereas the FSODAC table is divided in two parts, from 200hex to 2FFhex, and from 1A0hex to 1FFhex. With the exception of the gen-eral purpose user bytes, all values are 16-bit wide words formed by two adjacent byte locations (high byte and low byte).
The MAX1452 compensates for sensor offset, FSO, and temperature errors by loading the internal calibration registers with the compensation values. These com-pensation values can be loaded to registers directly via
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Figure 4. Basic 4–20mA Output, Loop-Powered Configuration
the serial digital interface during calibration or loaded automatically from EEPROM at power-on. I n this way the device can be tested and configured during cali-bration and test and the appropriate compensation val-ues stored in internal EEPROM. The device will auto-load the registers from EEPROM and be ready for
use without further configuration after each power-up.
The EEPROM is configured as an 8-bit wide array so
each of the 16-bit registers is stored as two 8-bit quan-tities. The configuration register, FSOTCDAC and OTC-
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M A X 1452
DAC registers are loaded from the pre-assigned loca-tions in the EEPROM.
The ODAC and FSODAC are loaded from the EEPROM lookup tables using an index pointer that is a function of temperature. An ADC converts the integrated tem-perature sensor to an 8-bit value every 1ms. This digi-tized value is then transferred into the temp-index register.
The typical transfer function for the temp-index is as fol-lows:
temp-index = 0.69 ?Temperature (°C) + 47.58where temp-index is truncated to an 8-bit integer value.Typical values for the temp-index register are given in Table 6.
Note that the EEPROM is byte wide and the registers that are loaded from EEPROM are 16 bits wide. Thus each index value points to two bytes in the EEPROM.Maxim programs all EEPROM locations to FFhex with the exception of the oscillator frequency setting and Secure-Lock byte. OSC[2:0] is in the Configuration Register (Table 3). These bits should be maintained at the factory preset values. Programming 00hex in the Secure-Lock byte (CL[7:0] = 00hex), configures the DIO as an asynchronous serial input for calibration and test purposes.
Communication Protocol
The DIO serial interface is used for asynchronous serial data communications between the MAX1452 and a host calibration test system or computer. The MAX1452will automatically detect the baud rate of the host com-puter when the host transmits the initialization sequence. Baud rates between 4800bps and 38,400bps can be detected and used regardless of the internal oscillator frequency setting. Data format is always 1 start bit, 8 data bits, 1 stop bit and no https://www.wendangku.net/doc/957053121.html,munications are only allowed when Secure-Lock is disabled (i.e., CL[7:0] = 00hex) or the UNLOCK pin is held high.
Initialization Sequence
Sending the initialization sequence shown below enables the MAX1452 to establish the baud rate that initializes the serial port. The initialization sequence is one byte transmission of 01hex, as follows.
1111111101000000011111111
The first start bit 0initiates the baud rate synchronization sequence. The 8 data bits 01hex (LSB first) follow this and then the stop bit, which is indicated above as a 1,
terminates the baud rate synchronization sequence.This initialization sequence on DIO should occur after a period of 1ms after stable power is applied to the device. This allows time for the power-on reset function to complete and the DI O pin to be configured by Secure-Lock or the UNLOCK pin.
Reinitialization Sequence
The MAX1452 allows for relearning the baud rate. The reinitialization sequence is one byte transmission of FFhex, as follows.
11111111011111111111111111
When a serial reinitialization sequence is received, the receive logic resets itself to its power-up state and waits for the initialization sequence. The initialization sequence must follow the reinitialization sequence in order to re-establish the baud rate.
Serial Interface Command Format
All communication commands into the MAX1452 follow a defined format utilizing an interface register set (IRS).The I RS is an 8-bit command that contains both an interface register set data (IRSD) nibble (4-bit) and an interface register set address (I RSA) nibble (4-bit). All internal calibration registers and EEPROM locations are accessed for read and write through this interface reg-ister set. The I RS byte command is structured as fol-lows:
IRS[7:0] = IRSD[3:0], IRSA[3:0]
Where:
?IRSA[3:0] is the 4-bit interface register set address
and indicates which register receives the data nib-ble IRSD[3:0].?IRSA[0] is the first bit on the serial interface after the start bit.
?IRSD[3:0] is the 4-bit interface register set data.?
I RSD[0] is the fifth bit received on the serial inter-face after the start bit.
The IRS address decoding is shown in Table 9.
Special Command Sequences
A special command register to internal logic (CRI L[3:0]) causes execution of special command sequences within the MAX1452. These command sequences are listed as CRI L command codes as shown in Table 10.
Write Examples
A 16-bit write to any of the internal calibration registers is performed as follows:
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1)Write the 16 data bits to DHR[15:0] using four byte
accesses into the interface register set.2)Write the address of the target internal calibration
register to ICRA[3:0]. 3)Write the load internal calibration register (LdI CR)
command to CRIL[3:0].When a LdICR command is issued to the CRIL register,the calibration register loaded depends on the address in the internal calibration register address (ICRA). Table 11specifies which calibration register is decoded.
Erasing and Writing the EEPROM
The internal EEPROM needs to be erased (bytes set to FFhex) prior to programming the desired contents.Remember to save the 3 MSBs of byte 161hex (high-byte of the configuration register) and restore it when programming its contents to prevent modification of the trimmed oscillator frequency.
The internal EEPROM can be entirely erased with the ERASE command, or partially erased with the PageErase command (see Table 10, CRIL command).It is necessary to wait 6ms after issuing the ERASE or PageErase command.
After the EEPROM bytes have been erased (value of every byte = FFhex), the user can program its contents,following the procedure below:
1)Write the 8 data bits to DHR[7:0] using two byte
accesses into the interface register set. 2)Write the address of the target internal EEPROM
location to IEEA[9:0] using three byte accesses into the interface register set. 3)Write the EEPROM write command (EEPW) to
CRIL[3:0].
Serial Digital Output
When a RdIRS command is written to CRIL[3:0], DIO is configured as a digital output and the contents of the
register designated by IRSP[3:0] are sent out as a byte framed by a start bit and a stop bit.
Once the tester finishes sending the RdIRS command,it must three-state its connection to DI O to allow the MAX1452 to drive the DIO line. The MAX1452 will three-state DI O high for 1 byte time and then drive with the start bit in the next bit period followed by the data byte and stop bit. The sequence is shown in Figure 5.
The data returned on a RdI RS command depends on the address in IRSP. Table 12defines what is returned for the various addresses.
Multiplexed Analog Output
When a RdAlg command is written to CRI L[3:0] the analog signal designated by ALOC[3:0] is asserted on the OUT pin. The duration of the analog signal is deter-mined by ATIM[3:0] after which the pin reverts to three-state. While the analog signal is asserted in the OUT pin, DIO is simultaneously three-stated, enabling a par-allel wiring of DI O and OUT. When DI O and OUT are connected in parallel, the host computer or calibration system must three-state its connection to DI O after asserting the stop bit. Do not load the OUT line when reading internal signals, such as BDR, FSOTC...etc. The analog output sequence with DI O and OUT is shown in Figure 6.
The duration of the analog signal is controlled by ATIM[3:0] as given in Table 13.
The analog signal driven onto the OUT pin is deter-mined by the value in the ALOC register. The signals are specified in Table 14.
Test System Configuration
The MAX1452 is designed to support an automated production test system with integrated calibration and temperature compensation. Figure 7shows the imple-mentation concept for a low-cost test system capable of testing many transducer modules connected in par-MAX1452
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Figure 5. DIO Output Data Format
M A X 1452
allel. The MAX1452 allows for a high degree of flexibili-ty in system calibration design. This is achieved by use of single-wire digital communication and three-state output nodes. Depending upon specific calibration requirements one may connect all the OUTs in parallel or connect DIO and OUT on each individual module.
Sensor Compensation Overview
Compensation requires an examination of the sensor performance over the operating pressure and tempera-ture range. Use a minimum of two test pressures (e.g.,zero and full-span) and two temperatures. More test pressures and temperatures will result in greater accu-racy. A typical compensation procedure can be sum-marized as follows:
Set reference temperature (e.g., 25°C):
?I nitialize each transducer by loading their respec-tive registers with default coefficients (e.g., based on mean values of offset, FSO and bridge resis-tance) to prevent overload of the MAX1452. ?
Set the initial bridge voltage (with the FSODAC) to half of the supply voltage. Measure the bridge volt-age using the BDR or OUT pins, or calculate based on measurements.
?Calibrate the output offset and FSO of the transduc-er using the ODAC and FSODAC, respectively.?
Store calibration data in the test computer or MAX1452 EEPROM user memory.
Set next test temperature:?Calibrate offset and FSO using the ODAC and FSO-DAC, respectively.
?Store calibration data in the test computer or MAX1452 EEPROM user memory.?Calculate the correction coefficients.
?Download correction coefficients to EEPROM.?
Perform a final test.
Sensor Calibration and Compensation Example
The MAX1452 temperature compensation design cor-rects both sensor and I C temperature errors. This enables the MAX1452 to provide temperature compen-sation approaching the inherent repeatability of the sensor. An example of the MAX1452’s capabilities is shown in Figure 8.
A repeatable piezoresistive sensor with an initial offset of 16.4mV and a span of 55.8mV was converted into a compensated transducer (utilizing the piezoresistive sensor with the MAX1452) with an offset of 0.5000V and a span of 4.0000V. Nonlinear sensor offset and FSO temperature errors, which were on the order of 20% to 30% FSO, were reduced to under ±0.1% FSO. The fol-lowing graphs show the output of the uncompensated sensor and the output of the compensated transducer.Six temperature points were used to obtain this result.
MAX1452Evaluation Kit
To expedite the development of MAX1452based transducers and test systems, Maxim has pro-duced the MAX1452 evaluation kit (EV kit). First-time users of the MAX1452 are strongly encouraged to use this kit.
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Figure 6. Analog Output Timing
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The EV kit is designed to facilitate manual program-ming of the MAX1452 with a sensor. It includes the fol-lowing:
1)Evaluation Board with or without a silicon pressure
sensor, ready for customer evaluation.2)Design/Applications M anual,which describes in
detail the architecture and functionality of the MAX1452. This manual was developed for test engineers familiar with data acquisition of sensor data and provides sensor compensation algorithms and test procedures.
3)MAX1452 Communication Software,which enables
programming of the MAX1452 from a computer keyboard (IBM compatible), one module at a time.4)Interface Adapter,which allows the connection of
the evaluation board to a PC serial port.
Figure 7. Automated Test System Concept
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Figure 8. Comparison of an Uncalibrated Sensor and a Calibrated Transducer
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