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MAX1452AAE+ |MAX1452AAEMAXN/a6avaiLow-Cost Precision Sensor Signal Conditioner
MAX1452AAE+T |MAX1452AAETMAXN/a2500avaiLow-Cost Precision Sensor Signal Conditioner
MAX1452ATG+MAIXMN/a2500avaiLow-Cost Precision Sensor Signal Conditioner
MAX1452ATG+TMAIXMN/a2500avaiLow-Cost Precision Sensor Signal Conditioner
MAX1452CAE+ |MAX1452CAEMAXIMN/a35avaiLow-Cost Precision Sensor Signal Conditioner
MAX1452EAE+N/AN/a2500avaiLow-Cost Precision Sensor Signal Conditioner


MAX1452AAE+T ,Low-Cost Precision Sensor Signal ConditionerElectrical Characteristics(V = V = +5V, V = 0V, T = +25°C, unless otherwise noted.)DD DDF SS APARAM ..
MAX1452ATG+ ,Low-Cost Precision Sensor Signal ConditionerFeaturesThe MAX1452 is a highly integrated analog-sensor sig- ● Single-Chip, Integrated Analog Sign ..
MAX1452ATG+T ,Low-Cost Precision Sensor Signal Conditionerapplications utilizing resistive element sensors. The Precision Sensor SolutionMAX1452 provides amp ..
MAX1452CAE ,Low-Cost Precision Sensor Signal Conditionerapplications utilizing resistive element sensors. Accommodates Sensor Output Sensitivities The MAX ..
MAX1452CAE+ ,Low-Cost Precision Sensor Signal ConditionerApplicationsMAX1452C/D 0°C to +70°C Dice**● Pressure Sensors+Denotes a lead(Pb)-free/RoHS-compliant ..
MAX1452EAE+ ,Low-Cost Precision Sensor Signal ConditionerApplicationsThe MAX1452 is packaged for the commercial, industrial, and automotive temperature rang ..
MAX4051ACSE+ ,Low-Voltage, CMOS Analog Multiplexers/SwitchesGeneral Description ________
MAX4051ACSE+T ,Low-Voltage, CMOS Analog Multiplexers/SwitchesApplications♦ Low Distortion: < 0.04% (600Ω)Battery-Operated Equipment♦ Low Crosstalk: < -90dB (50Ω ..
MAX4051AEEE ,Low-Voltage / CMOS Analog Multiplexers/SwitchesELECTRICAL CHARACTERISTICS—Dual Supplies(V+ = +4.5V to +5.5V, V- = -4.5V to -5.5V, T = T to T , unl ..
MAX4051AEEE+ ,Low-Voltage, CMOS Analog Multiplexers/SwitchesFeaturesThe MAX4051/MAX4052/MAX4053 and MAX4051A/ ♦ Pin Compatible with Industry-Standard MAX4052A/ ..
MAX4051AEEE+ ,Low-Voltage, CMOS Analog Multiplexers/SwitchesFeaturesThe MAX4051/MAX4052/MAX4053 and MAX4051A/ ♦ Pin Compatible with Industry-Standard MAX4052A/ ..
MAX4051AEEE+T ,Low-Voltage, CMOS Analog Multiplexers/SwitchesELECTRICAL CHARACTERISTICS—Dual Supplies(V+ = +4.5V to +5.5V, V- = -4.5V to -5.5V, T = T to T , unl ..


MAX1452AAE+-MAX1452AAE+T-MAX1452ATG+-MAX1452ATG+T-MAX1452CAE+-MAX1452EAE+
Low-Cost Precision Sensor Signal Conditioner
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 temper-
ature compensation that enables an overall performance
approaching the inherent repeatability of the sensor. The
fully analog signal path introduces no quantization noise
in the output signal while enabling digitally controlled trim-
ming with the integrated 16-bit DACs. Offset and span are
calibrated using 16-bit DACs, allowing sensor products to
be truly interchangeable.
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 com-
pensation, the MAX1452 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 MAX1452 is packaged for the commercial, industrial,
and automotive temperature ranges in 16-pin SSOP/
TSSOP and 24-pin TQFN 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 solution.
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
Beneits and Features
●Single-Chip, Integrated Analog Signal Path Reduces
Design Time and Saves Space in a Complete
Precision Sensor SolutionProvides Ampliication, Calibration, and
Temperature Compensation Fully Analog Signal Path Accommodates Sensor Output Sensitivities from
4mV/V to 60mV/V Single-Pin Digital Programming No External Trim Components Required 16-Bit Offset and Span Calibration Resolution Supports Both Current and Voltage Bridge Excitation Fast 150μs Step Response On-Chip Uncommitted Op Amp ●On-Chip Lookup Table Supports Multipoint
Calibration Temperature Correction Improving
System Performance●Secure-Lock™ Prevents Data Corruption ●Low 2mA Current Consumption Simplifies Power-
Supply Design in 4–20mA Applications
Detailed Block Diagram and Pin Configurations appear at
the end of data sheet.

+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
**Dice are tested at TA = +25°C, DC parameters only.
Secure-Lock is a trademark of Maxim Integrated Products, Inc.
PARTTEMP RANGEPIN-PACKAGE

MAX1452CAE+0°C to +70°C16 SSOP
MAX1452EAE+-40°C to +85°C16 SSOP
MAX1452AAE+-40°C to +125°C16 SSOP
MAX1452AUE+-40°C to +125°C16 TSSOP
MAX1452ATG+-40°C to +125°C24 TQFN-EP*
MAX1452C/D0°C to +70°CDice**
MAX1452Low-Cost Precision Sensor
Signal Conditioner
Ordering Information
EVALUATION KIT AVAILABLE
Supply Voltage, VDD to VSS.........................................-0.3V, +6V
Supply Voltage, VDD to VDDF................................-0.5V to +0.5V
All Other Pins...................................(VSS - 0.3V) to (VDD + 0.3V)
Short-Circuit Duration, FSOTC, OUT, BDR,
AMPOUT................................................................Continuous
Continuous Power Dissipation (TA = +70°C)
16-Pin SSOP/TSSOP (derate 8.00mW/°C above +70°C)..640mW
24-Pin TQFN (derate 20.8mW/°C above +70°C).................1.67W
Operating Temperature:
MAX1452CAE+/MAX1452C/D.............................0°C to +70°C
MAX1452EAE+.................................................-40°C to +85°C
MAX1452AAE+...............................................-40°C to +125°C
MAX1452AUE+..............................................-40°C to +125°C
MAX1452ATG+...............................................-40°C to +125°C
Junction Temperature.......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) ................................ +300°C
(VDD = VDDF = +5V, VSS = 0V, TA = +25°C, unless otherwise noted.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
GENERAL CHARACTERISTICS

Supply VoltageVDD4.55.05.5V
EEPROM Supply VoltageVDDF4.55.05.5V
Supply Current IDD(Note 1)2.02.5mA
Maximum EEPROM Erase/
Write Current IDDFW30mA
Maximum EEPROM Read
CurrentIDDFR12mA
Oscillator FrequencyfOSC0.8511.15MHz
ANALOG INPUT

Input ImpedanceRIN1MI
Input-Referred Offset Tempco (Notes 2, 3)P1µV/°C
Input-Referred Adjustable
Offset RangeOffset TC = 0 at minimum gain (Note 4)P150mV
Ampliier Gain NonlinearityPercent of +4V span, VOUT = +0.5V to
4.5V0.01%
Common-Mode Rejection RatioCMRRSpeciied for common-mode voltages
between VSS and VDD (Note 2)90dB
Input Referred Adjustable
FSO Range(Note 5)4 to mV/V
ANALOG OUTPUT

Differential Signal-Gain RangeSelectable in 16 steps39 to 234V/V
Differential Signal Gain
Coniguration [5:2] 0000bin343946
V/V
Coniguration [5:2] 0001bin475259
Coniguration [5:2] 0010bin586574
Coniguration [5:2] 0100bin8291102
Coniguration [5:2] 1000bin133143157
MAX1452Low-Cost Precision Sensor
Signal Conditioner
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.
Electrical Characteristics
(VDD = VDDF = +5V, VSS = 0V, TA = +25°C, unless otherwise noted.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS

Output-Voltage LowIOUT = 1mA sinking, TA = TMIN to TMAX0.1000.20V
Output-Voltage HighIOUT = 1mA sourcing, TA = TMIN to TMAX4.754.87V
Output Impedance at DC0.1Ω
Output Offset RatioΔVOUT/ ΔOffset0.901.051.20V/V
Output Offset TC RatioΔVOUT/ΔOffset TC0.911.2V/V
Step Response and IC
(63% Final Value)150µs
Maximum Capacitive Load1µF
Output NoiseDC to 1kHz (gain = minimum, source impedance = 5kΩ VDDF ilter)0.5mVRMS
BRIDGE DRIVE

Bridge CurrentIBDRRL = 1.7kΩ0.10.52mA
Current Mirror RatioAARISOURCE = internal101214A/A
VSPAN Range (Span Code)TA = TMIN to TMAX 4000C000hex
DIGITAL-TO-ANALOG CONVERTERS

DAC Resolution16Bits
ODAC Bit Weight ΔVOUT/ΔCodeDAC reference = VDD = +5.0V76µV/bit
OTCDAC Bit WeightΔVOUT/ΔCodeDAC reference = VBDR = +2.5V38µV/bit
FSODAC Bit Weight ΔVOUT/ΔCodeDAC reference = VDD = +5.0V76µV/bit
FSOTCDAC Bit WeightΔVOUT/ΔCodeDAC reference = VBDR = +2.5V38µV/bit
COARSE OFFSET DAC

IRODAC ResolutionIncluding sign4Bits
IRODAC Bit WeightΔVOUT/ΔCode
Input referred, DAC reference =
VDD = +5.0V (Note 6)9mV/bit
FSOTC BUFFER

Minimum Output-Voltage SwingNo loadVSS
+ 0.1V
Maximum Output-Voltage
SwingNo loadVDD - 1.0V
Current DriveVFSOTC = +2.5V-40+40µA
INTERNAL RESISTORS

Current-Source Reference
ResistorRISRC75kΩ
MAX1452Low-Cost Precision Sensor
Signal Conditioner
Electrical Characteristics (continued)
(VDD = VDDF = +5V, VSS = 0V, TA = +25°C, unless otherwise noted.)
Note 1:
Excludes sensor or load current.
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 range of +1.7V to +4.25V.
Note 6:
Bit weight is ratiometric to VDD.
Note 7:
Programming of the EEPROM at room temperature is recommended.
Note 8:
Allow a minimum of 6ms elapsed time before sending any command.
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS

Current-Source Reference Resistor Temperature CoeficientΔRISRC1300ppm/°C
FSOTC ResistorRFTC75kΩ
FSOTC Resistor Temperature CoeficientΔRFTC1300ppm/°C
TEMPERATURE-TO-DIGITAL CONVERTER

Temperature ADC Resolution8Bits
OffsetP3LSB
Gain1.45°C/bit
NonlinearityP0.5LSB
Lowest Digital Output00hex
Highest Digital OutputAFhex
UNCOMMITTED OP AMP

Open-Loop GainRL = 100kΩ90dB
Input Common-Mode RangeVSSVDDV
Output SwingNo load, TA = TMIN to TMAX VSS +
VDD -
0.02V
Output-Voltage High1mA source, TA = TMIN to TMAX4.854.90V
Output-Voltage Low1mA sink, TA = TMIN to TMAX0.050.15V
OffsetVIN+ = +2.5V, unity-gain buffer-20+20mV
Unity-Gain Bandwidth2MHz
EEPROM

Maximum Erase/Write Cycles(Note 7)10kCycles
Minimum Erase Time(Note 8)6ms
Minimum Write Time100µs
MAX1452Low-Cost Precision Sensor
Signal Conditioner
Electrical Characteristics (continued)
(VDD = +5V, TA = +25°C, unless otherwise noted.)
PINNAMEFUNCTIONSSOP/TSSOPTQFN-EP
1ISRCBridge Drive Current Mode Setting2OUTHigh ESD and Scan Path Output Signal. May need a 0.1µF capacitor, in
noisy environments. OUT may be parallel connected to DIO.3VSSNegative Supply Voltage4INMBridge Negative Input. Can be swapped to INP by coniguration register.5BDRBridge Drive6INPBridge Positive Input. Can be swapped to INM by coniguration register.7VDDPositive Supply Voltage. Connect a 0.1µF capacitor from VDD to VSS.8, 9, 13, 16, 20, 22, No Connection. Not internally connected; leave unconnected (TQFN
AMPLIFIER GAIN NONLINEARITY
MAX1452 toc02
INPUT VOLTAGE [INP - INM] (mV)
OUTPUT ERROR FROM STRAIGHT LINE (mV)
ODAC = 6250hex
OTCDAC = 0
FSODAC = 4000hex
FSOTCDAC = 8000hex
PGA INDEX = 0
IRO = 2
OUTPUT NOISE

MAX1452 toc03
400µs/div
C = 4.7µF, RLOAD = 1kΩ
OUT
10mV/div
OFFSET DAC DNL

MAX1452 toc01
DAC CODE
DNL (mV)30k40k10k20k50k60k70k
MAX1452Low-Cost Precision Sensor
Signal Conditioner
Typical Operating Characteristics
Pin Description
Detailed Description
The MAX1452 provides amplification, calibration, and
temperature compensation to enable an overall perfor-
mance approaching the inherent repeatability of the sen-
sor. The fully analog signal-path introduces no quantiza-
tion noise in the output signal while enabling digitally con-
trolled 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
latitude to compensate a sensor with a simple first order
linear correction or match an unusual temperature curve.
Programming up to 114 independent 16-bit EEPROM
locations corrects performance in 1.5°C temperature
increments over a range of -40°C to +125°C. For sensors
that exhibit a characteristic temperature performance,
a select number of calibration points can be used with
a number of preset values that define the temperature
curve. In cases where the sensor is at a different tempera-
ture than the MAX1452, the MAX1452 uses the sensor
bridge itself to provide additional temperature correction.
The single pin, serial Digital Input-Output (DIO) communi-
cation 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 paral-
lel connecting OUT and DIO. The MAX1452 provides a
Secure-Lock feature that allows the customer to prevent
modification of sensor coefficients and the 52-byte user
definable EEPROM data after the sensor has been
calibrated. The Secure-Lock feature also provides a hard-
ware 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 MAX1452,
the customer can choose to retest in order to verify per-
formance as part of a regular QA audit or to generate final
test data on individual sensors.
The MAX1452’s low current consumption and the integrat-
ed 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 bandwidth by using the
uncommitted op amp and simple passive components.
The MAX1452 (Figure 1) provides an analog amplification
path for the sensor signal. It also uses an analog architec-
ture for first-order temperature correction. A digitally con-
trolled analog path is then used for nonlinear temperature
correction. Calibration and correction is achieved by vary-
ing the offset and gain of a programmable-gain-amplifier
(PGA) and by varying the sensor bridge excitation current
PINNAMEFUNCTIONSSOP/TSSOPTQFN-EP
11VDDF
Positive Supply Voltage for EEPROM. Connect a 1µF capacitor from
VDDF to VSS. Connect VDDF to VDD or for improved noise performance connect a 30Ω resistor to VDD.12UNLOCKSecure-Lock Disable. Allows communication to the device.14DIODigital Input Output. DIO allows communication with the device.15CLK1M1MHz Clock Output. The output can be controlled by a coniguration bit.17AMPOUTUncommitted Ampliier Output18AMP-Uncommitted Ampliier Negative Input19AMP+Uncommitted Ampliier Positive Input21FSOTCFull Span TC Buffered Output—EPExposed Pad (TQFN Only). Internally connected; connect to VSS.
MAX1452Low-Cost Precision Sensor
Signal Conditioner
Pin Description (continued)
or voltage. The PGA 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
234V/V in 16 steps.
The MAX1452 uses four 16-bit DACs with calibration
coefficients stored by the user in an internal 768 x 8
EEPROM (6144 bits). This memory contains the following
information, as 16-bit wide words:Configuration RegisterOffset Calibration Coefficient TableOffset Temperature Coefficient RegisterFSO (Full-Span Output) Calibration TableFSO Temperature Error Correction Coefficient Register52 bytes (416 bits) uncommitted for customer pro-
gramming of manufacturing data (e.g., serial number
and date)
Offset Correction

Initial 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 tem-
perature 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 resolu-
tion 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 offset 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 maximum 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 temperature indexing boundaries
are outside of the specified Absolute Maximum Ratings.
The minimum indexing value is 00hex corresponding to
approximately -69°C. All temperatures below this value
output the coefficient value at index 00hex. The maximum
indexing value is AFhex, which is the highest lookup table
entry. All temperatures higher than approximately 184°C
output the highest lookup table index value. No indexing
wraparound 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 resolution approach-
ing 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 corresponding to approximately
-69°C. All temperatures below this value output the coef-
ficient value at index 00hex. The maximum indexing
value is AFhex, which is the highest lookup table entry.
All temperatures higher than approximately 184°C output
the highest lookup table index value. No indexing wrap-
around errors are produced.
Figure 1. Functional Diagram
MAX1452

BIAS
GENERATOR
OSCILLATOR
16 BIT DAC - OFFSET TC16 BIT DAC - OFFSET (176)16 BIT DAC - FSO (176) POINT16 BIT DAC - FSO TC
ANAMUX
FSOTC
TEMPERATURE
LOOK UP
POINTS FOR
OFFSET AND
SPAN.
OP-AMP
A = 1
AMPOUT
VSS
OUT
VDD
CLK1M
TEST
INTERNAL
EEPROM
6144 BITS
416 BITS
FOR USER
BDR
PGA
VDDF
VDDBDR
DIO
UNLOCK
AMP+
AMP-
INP
ISRC
INM
8-BIT ADC
TEMP
SENSOR
IRO
DAC
CURRENT
SOURCE
VDD
MAX1452Low-Cost Precision Sensor
Signal Conditioner
Linear and Nonlinear
Temperature Compensation

Writing 16-bit calibration coefficients into the offset TC
and FSOTC registers compensates first-order tempera-
ture errors. The piezoresistive sensor is powered by a
current source resulting in a temperature-dependent
bridge voltage due to the sensor’s temperature resistance
coefficient (TCR). The reference inputs of the offset TC
DAC and FSOTC DAC are connected to the bridge volt-
age. The DAC output voltages 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 (RISRC and RSTC) for FSO temperature compensation are optimized to 75kΩ
for silicon piezoresistive sensors. However, since the
required feedback resistor values are sensor dependent,
external resistors may also be used. The internal resistors
selection bit in the configuration register selects between
internal and external feedback resistors.
To calculate the required offset TC and FSOTC compen-
sation coefficients, two test-temperatures are needed.
After taking at least two measurements at each tempera-
ture, 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 sensor
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 FSO TC error should be com-
pensated 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 tem-
perature 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 affects the offset due to nature of the bridge. The
temperature is measured on both the MAX1452 die and
at the bridge sensor. It is recommended 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
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.
MAX1452

+5V VDD
OUT
GND
RSTC
RISRC
0.1µF0.1µF
INM
TESTVSS
INP3
BDRVDDF
OUT
FSOTC
ISRC
SENSOR
VDD
MAX1452Low-Cost Precision Sensor
Signal Conditioner
Typical Nonratiometric
Operating Circuit
(12VDC < VPWR < 40VDC)

Nonratiometric output configuration enables the sensor
power to vary over a wide range. A high-performance volt-
age reference, such as the MAX15006B, is incorporated
in the circuit to provide a stable supply and reference 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 nonratiometric.
The low current consumption of the MAX1452 allows it
to operate from loop power with a simple 4–20mA drive
circuit efficiently generated using the integrated uncom-
mitted op amp (Figure 4).
Internal Calibration Registers (ICRs)

The MAX1452 has five 16-bit internal calibration registers
that are loaded from EEPROM, or loaded from the serial
digital interface.
Data can be loaded into the internal calibration registers
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
Figure 3. Basic Nonratiometric Output Configuration
MAX1452

VPWR
+12V TO +40V
OUT
GND
RSTC
RISRC
1.0µF2.2µF0.1µF0.1µF
INM
TESTVSS
INP3
BDRVDDF
OUT
FSOTC
ISRC
SENSOR
MAX15006B

OUTGND
30Ω
VDDD
2N4392
MAX1452Low-Cost Precision Sensor
Signal Conditioner
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 Interface Command Format.
Internal EEPROM

page. Each page can be individually erased. The memory
structure is arranged as shown in Table 1. The lookup
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 general-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 compen-
sation values can be loaded to registers directly through
the serial digital interface during calibration or loaded
automatically from EEPROM at power-on. In this way the
Figure 4. Basic 4–20mA Output, Loop-Powered Configuration
MAX1452

VIN+
+12V TO +40V
2N2222A
47Ω100kΩ
4.99kΩ
4.99MΩ
30Ω
100Ω
499kΩ
100kΩ
VIN-
RSTC
RISRC
1.0µF
2.2µF
0.1µF
0.1µF
0.1µF
INM
TESTVSS
INP3
BDRVDDF
VDD5
FSOTC
ISRC
SENSOR
MAX15006B

OUTGNDIN
2N4392
OUT
AMPOUT
AMP-
AMP+
MAX1452Low-Cost Precision Sensor
Signal Conditioner
in internal EEPROM. The device auto-loads the registers
from EEPROM and be ready for use without further con-
figuration after each power-up. The EEPROM is config-
is stored as two 8-bit quantities. The configuration register,
FSOTCDAC and OTCDAC registers are loaded from the
pre-assigned locations in the EEPROM.
Table 1. EEPROM Memory Address Map
PAGELOW-BYTE
ADDRESS (hex)
HIGH-BYTE ADDRESS
(hex)
TEMP-INDEX[7:0]
(hex)CONTENTS
00000100
ODAC
Lookup Table
03E03F1F04004120
07E07F3F08008140
0BE0BF5F
0C00C160
0FE0FF7F10010180
13E13F9F
140141A0
15E15FAF to FF
160161Coniguration
162163Reserved
164165OTCDAC
166167Reserved
168169FSOTCDAC
16A16BControl Location
16C16D
52 General-Purpose
User Bytes
17E17F
19E19F
1A01A180
FSODAC
Lookup Table
1BE1BF8F1C01C190
1FE1FFAF to FF
23E23F1F24024120
27E27F3F28028140
2BE2BF5F2C02C160
2FE2FF7F
MAX1452Low-Cost Precision Sensor
Signal Conditioner
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 temperature
sensor output to an 8-bit value every 1ms. This digitized
value is then transferred into the temp-index register.
The typical transfer function for the temp-index is as fol-
lows:
temp-index = 0.6879 Temperature (°C) + 44.0
where 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 MAX1452 auto-
matically detects the baud rate of the host computer 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 parity. Communications 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 trans-
mission of 01hex, as follows:
The first start bit 0 initiates 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 DIO 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:
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
IRS is an 8-bit command that contains both an interface
register set data (IRSD) nibble (4-bit) and an interface
register set address (IRSA) nibble (4-bit). All internal cali-
bration registers and EEPROM locations are accessed for
read and write through this interface register set. The IRS
byte command is structured as follows:
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 nibble 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.IRSD[0] is the fifth bit received on the serial interface
after the start bit.
The IRS address decoding is shown in Table 10.
Special Command Sequences

A special command register to internal logic (CRIL[3:0])
causes execution of special command sequences within
the MAX1452. These command sequences are listed as
CRIL command codes as shown in Table 11.
Write Examples

A 16-bit write to any of the internal calibration registers is
performed as follows:
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 reg-
MAX1452Low-Cost Precision Sensor
Signal Conditioner
3) Write the load internal calibration register (LdICR) com-mand 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 12
specifies 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 161 hex (high byte
of the configuration register) and restore it when program-
ming 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 11, CRIL command). It is necessary
to wait 6ms after issuing the ERASE or PageErase com-
mand.
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 loca-tion 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 DIO to allow the
MAX1452 to drive the DIO line. The MAX1452 three-
states DIO 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 RdIRS command depends on the
address in IRSP. Table 13 defines what is returned for the
various addresses.
Multiplexed Analog Output

When a RdAlg command is written to CRIL[3:0] the ana-log signal designated by ALOC[3:0] is asserted on the
OUT pin. The duration of the analog signal is determined 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 parallel wiring
of DIO and OUT. When DIO and OUT are connected in
parallel, the host computer or calibration system must
three-state its connection to DIO 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 DIO and OUT is shown
in Figure 6.
The duration of the analog signal is controlled by ATIM[3:0]
as given in Table 14.
Figure 5. DIO Output Data Format
DRIVEN BY TESTERDRIVEN BY MAX1452
THREE-STATE
NEED WEAK
PULLUP
THREE-STATE
NEED WEAK
PULLUP
START-BIT
LSB
START-BIT
LSB
MSB
STOP-BIT
MSB
STOP-BIT1111010011010111111111100000100011111111111DIO
MAX1452Low-Cost Precision Sensor
Signal Conditioner
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