MAX1455AAE+ ,Low-Cost Precision Sensor Signal ConditionerFeatures● Provides Amplification, Calibration, and Temperature The MAX1455 is a highly integrated, ..
MAX14566AEETA+T ,USB Host Charger Identification Analog SwitchesELECTRICAL CHARACTERISTICS(V = 2.8V to 5.5V, T = T to T unless otherwise noted. Typical values are ..
MAX14566BEETA+T ,USB Host Charger Identification Analog SwitchesFeaturesThe MAX14566E/MAX14566AE/MAX14566BE are sec- S Hi-Speed USB Switchingond-generation USB dev ..
MAX14566EETA+T ,USB Host Charger Identification Analog Switchesfeatures an additional digital input (CB1) MAX14566EETA+ 8 TDFN-EP* ADJCENto allow forced charger m ..
MAX14578AEEWC+T ,USB Battery Charger DetectorsApplicationsresistor-divider networks on D+/D-.DSC and CamcorderThe MAX14578E/MAX14578AE are availa ..
MAX1457CWI ,0.1%-Accurate Signal Conditioner for Piezoresistive Sensor CompensationFeaturesThe MAX1457 is a highly integrated analog-sensor sig- ' High Accuracy (within ±0.1% of sens ..
MAX4051CSE ,Low-Voltage / CMOS Analog Multiplexers/SwitchesMAX4051/A, MAX4052/A, MAX4053/A19-0463; Rev 0; 1/96Low-Voltage, CMOS AnalogMultiplexers/Switches___ ..
MAX4051CSE+ ,Low-Voltage, CMOS Analog Multiplexers/SwitchesApplications♦ Low Distortion: < 0.04% (600Ω)Battery-Operated Equipment♦ Low Crosstalk: < -90dB (50Ω ..
MAX4051EEE+ ,Low-Voltage, CMOS Analog Multiplexers/SwitchesGeneral Description ________
MAX4051EPE ,Low-Voltage / CMOS Analog Multiplexers/SwitchesGeneral Description ________
MAX4051ESE ,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 ..
MAX4051ESE ,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 ..
MAX1455AAE+
Low-Cost Precision Sensor Signal Conditioner
General DescriptionThe MAX1455 is a highly integrated, sensor signal pro-
cessor for resistive element sensors. The MAX1455 pro-
vides amplification, calibration, and temperature compen-
sation that enable 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 trimming with
integrated 16-bit digital-to-analog converters (DACs).
Offset and span are also calibrated using 16-bit DACs,
allowing sensor products to be truly interchangeable.
The MAX1455 architecture includes a programmable
sensor excitation, a 16-step programmable-gain amplifier
(PGA), a 768-byte (6144 bits) internal EEPROM, four 16-bit
DACs, an uncommitted op amp, and an on-chip tempera-
ture sensor. In addition to offset and span compensation,
the MAX1455 provides a unique temperature compensa-
tion strategy that was developed to provide a remarkable
degree of flexibility while minimizing testing costs.
The MAX1455 is available in die form, and in 16-pin
SSOP and TSSOP packages.
CustomizationMaxim can customize the MAX1455 for high-volume
dedicated applications. Using our dedicated cell library of
more than 2000 sensor-specific function blocks, Maxim
can quickly provide a modified MAX1455 solution. Contact
Maxim for further information.
Applications●Pressure Sensors and Transducers●Piezoresistive Silicon Sensors●Strain Gauges●Resistive Element Sensors●Accelerometers●Humidity Sensors●MR and GMR Sensors
Outputs●Ratiometric Voltage Output●Programmable Output Clip Limits
Features●Provides Amplification, Calibration, and Temperature
Compensation●Selectable Output Clipping Limits●Accommodates Sensor Output Sensitivities
from 5mV/V to 40mV/V●Single-Pin Digital Programming●No External Trim Components Required●16-Bit Offset and Span Calibration Resolution●Fully Analog Signal Path●PRT Bridge Can Be Used for Temperature-Correction
Input●On-Chip Lookup Table Supports Multipoint
Calibration Temperature Correction●Fast 3.2kHz Frequency Response●On-Chip Uncommitted Op Amp●Secure-Lock™ Prevents Data Corruption
A detailed Functional Diagram appears at end of data sheet.*Future Product—Contact factory for availability.
*Dice are tested at TA = +25°C, DC parameters only.
Secure-Lock is a trademark of Maxim Integrated Products, Inc.
PARTTEMP. RANGEPIN-PACKAGEMAX1455AAE-40°C to +125°C16 SSOP
MAX1455AUE*-40°C to +125°C16 TSSOP
MAX1455EAE-40°C to +85°C16 SSOP
MAX1455EUE*-40°C to +85°C16 TSSOP
MAX1455C/D-40°C to +85°CDice**
TEST1TEST2
TEST3
TEST4
DIO
UNLOCK
VDD2
AMP-
AMPOUT
TOP VIEW
MAX1455
SSOP/TSSOPOUT
INP
VSS
BDR
INM
VDD1
AMP+
MAX1455Low-Cost Precision Sensor Signal Conditioner
Ordering Information
Pin Coniguration
EVALUATION KIT AVAILABLE
Supply Voltage, VDD_ to VSS .....................................-0.3V, +6V
VDD1 - VDD2 ............................................................-0.3V, +0.6V
All Other Pins ..............................(VSS - 0.3V) to (VDD_ + 0.3V)
Short-Circuit Duration, OUT, BDR, AMPOUT ............Continuous
Continuous Power Dissipation (TA = +70°C)
16-Pin SSOP (derate 8.00mW/°C above +70°C) ........640mW
Operating Temperature Ranges (TMIN to TMAX)
MAX1455C/D ..................................................-40°C to +85°C
MAX1455EAE .................................................-40°C to +85°C
MAX1455AAE ...............................................-40°C to +125°C
MAX1455EUE.................................................-40°C to +85°C
MAX1455AUE...............................................-40°C to +125°C
Storage Temperature Range ............................-65°C to +150°C
Lead Temperature (soldering, 10s) ................................ +300°C
(VDD = +5V, VSS = 0V, TA = +25°C, unless otherwise noted.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
GENERAL CHARACTERISTICSSupply VoltageVDD4.55.05.5V
Supply CurrentIDDIDD1 + IDD2 (Note 1)3.06.0mA
Oscillator FrequencyfOSC0.8511.15MHz
ANALOG INPUTInput ImpedanceRIN1MΩ
Input-Referred Adjustable Offset
RangeOffset TC = 0 (Note 2), minimum gain ±150mV
Input-Referred Offset TempcoTA = TMIN to TMAX±1µV/°C
Ampliier Gain Nonlinearity0.025%
Common-Mode Rejection RatioCMRRSpeciied for common-mode voltages
between VSS and VDD90dB
Minimum Input-Referred FSO
Range(Note 3)7mV/V
Maximum Input-Referred FSO
Range(Note 3)40mV/V
ANALOG OUTPUTMinimum Differential Signal-Gain
RangePGA [3:0] = 000039V/V
Maximum Differential Signal-
Gain RangePGA [3:0] = 1111234V/V
Output Clip Voltage SettingsVOUTNo load,
TA = TMIN to TMAX
Clip[1:0] = 00Low0.10
High4.90
Clip[1:0] = 01Low0.15
High4.85
Clip[1:0] = 10Low0.20
High4.80
Clip[1:0] = 11
Low0.25
High4.75VOUT = +0.5V to +4.5V, TA = TMIN to TMAX,
MAX1455Low-Cost Precision Sensor Signal Conditioner
Absolute Maximum RatingsStresses 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 = +5V, VSS = 0V, TA = +25°C, unless otherwise noted.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSLoad Current Sink VOUT = +0.5V to +4.5V, TA = TMIN to TMAX,
Clip[1:0] = 002mA
DC Output Impedance 1Ω
Offset DAC Output Ratio DVOUT/DODAC1.0V/V
Offset TC DAC Output Ratio DVOUT/DOTCDAC1.0V/V
Step Response 0% to 63% of inal value300µs
Output Capacitive Load 1000nF
Output NoiseDC to 1kHz (gain = minimum, source impedance = 5kΩ)2.5mVRMS
BRIDGE DRIVEBridge CurrentIBDRVBDR ≤ 3.75V0.10.52mA
Current Mirror Ratio12mA/mA
Minimum FSODAC Code Recommended minimum value4000Hex
DIGITAL-TO-ANALOG CONVERTERSDAC Resolution16Bits
ODAC Bit WeightDVOUT/DCODE, DAC reference = VDD =
+5.0V (Note 4)153µV/Bit
OTCDAC Bit WeightDVOUT/DCODE, DAC reference = VBDR =
2.5V (Note 4)76µV/Bit
FSODAC Bit WeightDVOUT/DCODE, DAC reference = VDD =
+5.0V (Note 4)153µV/Bit
FSOTCDAC Bit WeightDVOUT/DCODE, DAC reference = VBDR =
2.5V (Note 4)76µV/Bit
COARSE-OFFSET DACIRODAC ResolutionExcluding sign bit3Bits
IRODAC Bit WeightDVOUT/DCODE, input referred,
DAC reference = VDD = +5.0V (Note 4)9mV/Bit
INTERNAL RESISTORSCurrent-Source ReferenceRISRC75kΩ
Full-Span Output (FSO) Trim
Resistor ∆RSTC75kΩ
Resistor Temperature CoeficientApplies to RISRC and DRSTC1333ppm/°C
Minimum Resistance ValueApplies to RISRC and DRSTC60kΩ
Maximum Resistance ValueApplies to RISRC and DRSTC90kΩ
Resistor MatchingRISRC to DRSTC1%
AUXILIARY OP AMPOpen-Loop Gain90dB
Input Common-Mode RangeVCMVSSVDDV
Output SwingNo load, TA = TMIN to TMAX VSS +
VDD - V
MAX1455Low-Cost Precision Sensor Signal Conditioner
Electrical Characteristics (continued)
(VDD = +5V, VSS = 0V, TA = +25°C, unless otherwise noted.)
Note 1: Excludes sensor or load current.
Note 2: This is the maximum allowable sensor offset.
Note 3: 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 4: Bit weight is ratiometric to VDD.
Note 5: All units production tested at TA = +25°C. Limits over temperature are guaranteed by design.
Note 6: Programming of the EEPROM at temperatures below +70°C is recommended.
Note 7: For operation above +70°C, limit erase/write cycle to 100.
Note 8: All erase commands require 7.1ms minimum time.
(VDD_ = +5V, VSS = 0V, TA = +25°C, unless otherwise noted.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSOutput Current DriveVOUT = (VSS + 0.25) to (VDD - 0.25)-1+1mA
Common-Mode Rejection RatioCMRRVCM = VSS to VDD70dB
Input Offset VoltageVOSVIN = 2.5V unity-gain
buffer (Note 5)
TA = +25°C±1±20TA = TMIN to TMAX±25
Unity-Gain Bandwidth2MHz
TEMPERATURE-TO-DIGITAL CONVERTERTemperature ADC Resolution8Bits
Offset±3Bits
Gain1.45°C/Bit
Nonlinearity±1LSB
Lowest Digital Output00Hex
Highest Digital OutputAFHex
EEPROMMaximum Erase/Write Cycles (Notes 6, 7)10kCycles
Erase Time (Note 8)7.1ms
AMPLIFIER GAIN NONLINEARITY
MAX1455 toc02
OUTPUT ERROR FROM STRAIGHT LINE (mV)
ODAC = +6000HEX
OTCDAC = 0
FSODAC = 6000HEX
FSOTCDAC = 8000HEX
IRO = 2HEX
PGA = 0
OUTPUT NOISEMAX1455 toc03
400µs/div
OUT
10mV/div
INP - INM SHORTED TOGETHER
PGA = 0HEX
OFFSET DAC DNLMAX1455 toc01
DNL (mV)30k40k10k20k50k60k70k
MAX1455Low-Cost Precision Sensor Signal Conditioner
Electrical Characteristics (continued)
Typical Operating Characteristics
Detailed DescriptionThe MAX1455 provides amplification, calibration, and tem-
perature compensation to enable 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
trimming with the integrated 16-bit DACs. The MAX1455
includes four selectable high/low clipping limits set in dis-
crete 50mV steps from 0.1V/4.9V to 0.25V/4.75V. Offset
and span can be calibrated to within ±0.02% of span.
The MAX1455 architecture includes a programmable
sensor excitation, a 16-step PGA, a 768-byte (6144 bits)
internal EEPROM, four 16-bit DACs, an uncommitted op
amp, and an on-chip temperature sensor. The MAX1455
also provides a unique temperature compensation strat-
egy that was developed to provide a remarkable degree
of flexibility while minimizing testing costs.
The customer can select from 1 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 tempera-
ture curve. Programming up to 114 independent 16-bit
perature 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. The sensor and the MAX1455 should
be at the same temperature during calibration and use.
This allows the electronics and sensor errors to be com-
pensated together and optimizes performance. For appli-
cations where the sensor and electronics are at different
temperatures, the MAX1455 can use the sensor bridge as
an input to correct for temperature errors.
The single pin, serial DIO communication 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 DIO. The MAX1455 provides a Secure-Lock feature
that allows the customer to prevent modification of sen-
sor coefficients and the 52-byte user-definable EEPROM
data after the sensor 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.
PINNAMEFUNCTION1, 15, 16
TEST1,
TEST3,
TEST2
Test Pins. Connect to VSS or leave unconnected.OUTAnalog Output. Internal voltage nodes can be accessed in digital mode. OUT can be parallel
connected to DIO. Bypass OUT to ground with a 0.1µF capacitor to reduce output noise.INPPositive Input. Can be swapped to INM by the Coniguration register.BDRBridge Drive OutputINMNegative Input. Can be swapped to INP by the Coniguration register.VSSNegative Supply VoltageVDD1Positive Supply Voltage 1. Connect a 0.1µF capacitor from VDD to VSS.AMP+Auxiliary Op Amp Positive InputAMPOUTAuxiliary Op Amp OutputAMP-Auxiliary Op Amp Negative InputVDD2Positive Supply Voltage 2. Connect a 0.47µF capacitor from VDD2 to VSS. Connect VDD2 to VDD1 or for improved noise performance, connect a 1kΩ resistor to VDD1.UNLOCKSecure-Lock Disable. There is a 150µA pulldown to VSS. Connect to VDD to disable Secure-Lock
and enable serial communication.DIODigital Input Output. Single-pin serial communication port. There are no internal pullups on DIO.
Connect pullup resistor from DIO to VDD when in digital mode.TEST4Test Pin. Do not connect.
MAX1455Low-Cost Precision Sensor Signal Conditioner
Pin Description
The MAX1455 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 verify perfor-
mance as part of a regular QA audit or to generate final
test data on individual sensors. In addition, Maxim has
developed a pilot production test system to reduce time
to market. Engineering test evaluation and pilot produc-
tion of the MAX1455 can be performed without expending
the cost and time to develop in-house test capabilities.
Contact Maxim for additional information.
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 MAX1455 (Figure 1) provides an analog amplification
path for the sensor signal. It uses a digitally controlled
analog path for nonlinear temperature correction. For
PRT applications, analog architecture is available for first-
order temperature correction. Calibration and correction
are achieved by varying the offset and gain of a PGA and
by varying the sensor bridge excitation current 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 MAX1455 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 calibration coefficient tableFSO temperature correction register52 bytes (416 bits) uncommitted for customer pro-
gramming of manufacturing data (e.g., serial number
and date)
Offset CorrectionInitial 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 temper-
ature-indexed lookup table with one hundred seventy-six
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 is 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 1°C of temperature drift
of the sensor, given that the Offset DAC has corrected the
sensor every 1.5°C. The temperature indexing boundar-
ies are outside 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 CorrectionTwo functional blocks control the FSO gain calibration.
First, a coarse gain is set by digitally selecting the gain
of the PGA. Second, FSODAC sets the sensor bridge
Figure 1. Functional Diagram
MAX1455BIAS
GENERATOR
OSCILLATOR
ANAMUX
AMP-
AMPOUT
OUT
TEST 1
BDR
PGA
INP
INM
8-BIT A/D
TEMP
SENSOR
IRO
DAC
CURRENT
SOURCE
CLIP-TOP
CLIP-BOT
TEST 2
TEST 3
TEST 4
AMP+
CONTROL
VDD1
VDD2
DIO
UNLOCK
VSS
176-POINT
TEMPERATURE-
INDEXED
FSO
COEFFICIENTS
176-POINT
TEMPERATURE-
INDEXED
OFFSET
COEFFICIENTS
416 BITS FOR
USER DATA
CONFIG REG
6144-BIT
EEPROM
16-BIT DAC - FSO
16-BIT DAC - OFFSET16-BIT DAC - OFFSET TC16-BIT DAC - FSO TC
MAX1455Low-Cost Precision Sensor Signal Conditioner
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 one hundred sev-
enty-six 16-bit entries. The on-chip temperature sensor
provides a unique FSO trim from the table with an index-
ing resolution approaching one 16-bit value every 1.5°C
from -40°C to +125°C. The temperature indexing bound-
aries are outside 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.
Linear and Nonlinear Temperature
CompensationWriting 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 coefficient
resistance (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 and a portion of the bridge
voltage, which is temperature dependent, is used to com-
pensate the first-order temperature errors.
The internal feedback resistors (RISRC and RSTC) for FSO temperature compensation are set to 75kΩ.
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 TC and FSOTC should be compensat-
ed 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
affect the FSO; however, changing the FSO affects the
offset due to the nature of the bridge. The temperature
is measured on both the MAX1455 die and at the bridge
sensor. It is recommended to compensate the first-order
temperature errors using the bridge sensor temperature.
Typical Ratiometric Operating CircuitRatiometric 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 MAX1455 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 capacitorOne optional output EMI suppression capacitor
Typical Nonratiometric Operating Circuit
(5.5VDC < VPWR < 28VDC)Nonratiometric output configuration enables the sensor
power to vary over a wide range. A low-dropout volt-
age regulator, such as the MAX1615, is incorporated in
the circuit to provide a stable supply and reference for
MAX1455 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.
Internal Calibration RegistersThe MAX1455 has five 16-bit internal calibration registers
(ICRs) that are loaded from EEPROM, or loaded from the
serial digital interface.
Data can be loaded into the ICRs under three different
circumstances.
Normal Operation, Power-On Initialization Sequence:The MAX1455 has been calibrated, the Secure-Lock
byte is set (CL[7:0] = FFhex), and UNLOCK is low.
MAX1455Low-Cost Precision Sensor Signal Conditioner
Power is applied to the device.The power-on reset (POR) functions have been com-pleted.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 MAX1455 has been calibrated, the Secure-Lock byte Power is applied to the device.The POR functions have been completed.The temperature index timer reaches a 1ms time
period.Registers CONFIG, OTCDAC, and FSOTCDAC are
refreshed from EEPROM.Registers ODAC and FSODAC are refreshed from the
temperature indexed EEPROM locations.
Figure 2. Basic Ratiometric Output Configuration
Figure 3. Basic Nonratiometric Output Configuration
MAX1455+5V VDD
OUT
GND
0.1µF0.1µF
INM
VSS
INP
BDRVDD2
OUTSENSOR
VDD1
MAX1455VPWR
+5.5V TO +28V
OUT
GND
0.47µF0.1µF0.1µF0.1µF
INP
VSS
INM
BDRVDD2
OUTSENSOR
MAX1615OUTGND
1kΩ
VDD1
5/3
SHDN
MAX1455Low-Cost Precision Sensor Signal Conditioner
Calibration Operation, Registers Updated by Serial
Communications:The MAX1455 has not had the Secure-Lock byte set
(CL[7:0] = 00hex) or UNLOCK is high.Power is applied to the device.The POR functions have been 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 EEPROMThe 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
memory structure is arranged as shown in Table 1. The
look-up tables for ODAC and FSODAC are also shown,
with the respective temperature 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 MAX1455 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
device can be tested and configured during calibration
and test and the appropriate compensation values stored
in internal EEPROM. The device autoloads the registers
from EEPROM and is ready for use without further con-
figuration 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 quantities. The Configuration register,
FSOTCDAC, and OTCDAC registers are loaded from
the preassigned locations in the EEPROM. Table 2 is the
EEPROM ODAC and FSODAC lookup table memory map.
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 to an 8-bit value every 1ms. This digitized value is
then transferred into the temp-index register. Table 3 lists
the registers.
The typical transfer function for the temp-index is as fol-
lows:
where temp-index is truncated to an 8-bit integer value.
Typical values for the temp-index register are given in
Table 4.
Note that the EEPROM is 1 byte wide and the registers
that are loaded from EEPROM are 16 bits wide. Thus,
each index value points to 2 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 5). 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.
MAX1455 Digital ModeA single-pin serial interface provided by the DIO accesses
the MAX1455’s control functions and memory. All com-
mand inputs to this pin flow into a set of 16 registers,
which form the interface register set (IRS). Additional lev-
els of command processing are provided by control logic,
which takes its inputs from the IRS. A bidirectional 16-bit
latch buffers data to and from the 16-bit Calibration regis-
ters and internal (8-bit-wide) EEPROM locations. Figure
5 shows the relationship between the various serial com-
mands and the MAX1455 internal architecture.
Communication ProtocolThe DIO serial interface is used for asynchronous serial
data communications between the MAX1455 and a host
calibration test system or computer. The MAX1455 auto-
matically detects the baud rate of the host computer when
the host transmits the initialization sequence. Baud rates
between 4800 and 38400 can be detected and used. The
data format is always 1 start bit, 8 data bits, and 1 stop
bit. The 8 data bits are transmitted LSB first, MSB last. A
weak pullup resistor can be used to maintain logic 1 on
the DIO pin while the MAX1455 is in digital mode. This
is to prevent unintended 1 to 0 transitions on this pin,
which would be interpreted as a communication start bit.
Communications are only allowed when the Secure-Lock
byte is disabled (i.e., CL[7:0] = 00HEX ) or UNLOCK is
held high. Table 8 is the control location.
Initialization Sequence The first Command Byte sent to the MAX1455 after pow-
er-up, or following receipt of the reinitialization command,
is used by the MAX1455 to learn the communication baud
rate. The initialization sequence is a 1-byte transmiss of
01 hex, as follows:
MAX1455Low-Cost Precision Sensor Signal Conditioner
The start bit, shown in bold above, initiates the baud rate
synchronization. The 8 data bits 01hex (LSB first) follow
this and then the stop bit, also shown in bold above. The
MAX1455 uses this sequence to calculate the time inter-
val for a 1-bit transmission as a multiple of the period of
clock cycles is then stored internally as an 8-bit number
(BITCLK). Note that the device power supply should be
stable for a minimum period of 1ms before the initializa-
tion sequence is sent. This allows time for the POR func-
tion to complete and DIO to be configured by the Secure-
Table 1. EEPROM Memory Address Map
PAGELOW-BYTE ADDRESS
(hex)
HIGH-BYTE ADDRESS
(hex)
TEMP-INDEX[7:0]
(hex)CONTENTS00000100
ODAC
Lookup Table
03E03F1F04004120
07E07F3F08008140
0BE0BF5F0C00C160
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 FF20020100
23E23F1F24024120
27E27F3F28028140
2BE2BF5F2C02C160
2FE2FF7F
MAX1455Low-Cost Precision Sensor Signal Conditioner
Reinitialization SequenceThe MAX1455 provides for reestablishing, or relearning,
the baud rate. The reinitialization sequence is a 1-byte
transmiss of FFhex, as follows: 1111
111111
011111111
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 rees-
tablish the baud rate.
Table 2. EEPROM ODAC and FSODAC Lookup Table Memory Map
Table 3. Registers
Table 4. Temp-Index Typical ValuesDATA
DIO
TRANSMITRECEIVEHIGH-ZHIGH-ZTRANSMITHOST
RECEIVETRANSMITHIGH-ZRECEIVE1111100
011010
000000000
11111111111111111111XXXX
WEAK PULLUP
REQUIRED
WEAK PULLUP
REQUIRED
TEMP-INDEX[7:0]EEPROM ADDRESS ODAC
LOW BYTE AND HIGH BYTE
EEPROM ADDRESS FSODAC
LOW BYTE AND HIGH BYTE00hex
to
7Fhex
000hex and 001hex
to
0FEhex and 0FFhex
200hex and 201hex
to
2FEhex and 2FFhex
80hex
to
AFhex
100hex and 101hex
to
15Ehex and 15Fhex
1A0hex and 1A1hex
to
1FEhex and 1FFhex
REGISTERDESCRIPTIONCONFIGConiguration register
ODACOffset DAC register
OTCDACOffset temperature coeficient DAC register
FSODACFull-span output DAC register
FSOTCDACFull-span output temperature coeficient DAC register
TEMPERATURE
(°C)
TEMP-INDEX[7:0]
DECIMALHEXADECIMAL+256541
+851066A
+12513486
MAX1455Low-Cost Precision Sensor Signal Conditioner
Serial Interface Command FormatAll communication commands into the MAX1455 follow the
format of a start bit, 8 command bits (command byte), and
a stop bit. The Command Byte controls the contents of the
IRS and comprises a 4-bit interface register set address
(IRSA) nibble and a 4-bit interface register set data (IRSD)
nibble. The IRS Command Byte is structured as follows:
IRS[7:0] = IRSD[3:0], IRSA[3:0]
All commands are transmitted LSB first. The first bit fol-
lowing the start bit is IRSA[0] and the last bit before the
stop is IRSD[3] as follows:
IRSAIRSD
11111
001230123
111111
Half of the register contents of the IRS are used for data
hold and steering information. Data writes to two locations
within the IRS cause immediate action (command execu-
tion). These locations are at addresses 9 and 15 and are
the Command Register to Internal Logic (CRIL) and reini-
tialize commands, respectively. Table 9 shows a full listing
of IRS address decoding.
Command sequences can be written to the MAX1455
as a continuous stream, i.e., start bit, command byte,
stop bit, start bit, command byte, stop bit, etc. There are
no delay requirements between commands while the
MAX1455 is receiving data.
Command Register to Internal LogicA data write to the CRIL location (IRS address 9) causes
immediate execution of the command associated with
the 4-bit data nibble written. All EEPROM and Calibration
register read and write, together with EEPROM erase,
commands are handled through the CRIL location. CRIL
is also used to enable the MAX1455 analog output and to
place output data (serial digital output) on DIO. Table 10
shows a full listing of CRIL commands.
Table 5. Configuration Register (CONFIG[15:0])
Table 6. PGA Gain Setting (PGA[3:0])
FIELDNAMEDESCRIPTION15:13OSC[2:0]Oscillator frequency setting. Factory preset; do not change.
12:11CLIP[1:0]Sets output clip levels.PGA SignLogic 1 inverts INM and INP polarity (Table 6).IRO SignLogic 1 for positive input-referred offset (IRO). Logic 0 for negative IRO.
8:6IRO[2:0]Input-referred coarse-offset adjustment (Table 7).
5:2PGA[3:0]Programmable-gain ampliier setting.ODAC SignLogic 1 for positive offset DAC output. Logic 0 for negative offset DAC output.OTCDAC
SignLogic 1 for positive offset TC DAC output. Logic 0 for negative offset TC DAC output.
PGA[3:0]PGA GAIN (V/V) MAX1455Low-Cost Precision Sensor Signal Conditioner
Serial Digital Output DIO is configured as a digital output by writing a Read
IRS (RDIRS) command (5 hex) to the CRIL location. On
receipt of this command, the MAX1455 outputs a byte of
data, the contents of which are determined by the IRS
pointer (IRSP[3:0]) value at location IRSA[3:0] = 8hex.
The data is output as a single byte, framed by a start bit
and a stop bit. Table 11 lists the data returned for each
IRSP address value.
Once the RDIRS command has been sent, all connec-
tions to DIO must be three-stated to allow the MAX1455
to drive the DIO line. Following receipt of the RDIRS com-
mand, the MAX1455 drives DIO high after 1 byte time.
The MAX1455 holds DIO high for a single bit time and
then asserts a start bit (drives DIO low). The start bit is
then followed by the data byte and a stop bit. Immediately
following transmission of the stop bit, the MAX1455 three-
states DIO, releasing the line. The MAX1455 is then
ready to receive the next command sequence 1 byte time
after release of DIO.
Note that there are time intervals before and after the
MAX1455 sends the data byte when all devices on the
DIO line are three-stated. It is recommended that a weak
pullup resistor be applied to the DIO line during these time
intervals to prevent unwanted transitions (Figure 4). In
applications where DIO and analog output (OUT) are not
connected, a pullup resistor should be permanently con-
nected to DIO. If the MAX1455 DIO and analog outputs
are connected, then do not load this common line during
analog measurements. In this situation, perform the fol-
lowing sequence:
1) Connect a pullup resistor to the DIO/OUT line, prefer-
ably with a relay.
2) Send the RDIRS command.
3) Three-state the user connection (set to high imped-
ance).
4) Receive data from the MAX1455.
5) Activate the user connection (pull DIO/OUT line high).
6) Release the pullup resistor.
Table 7. Input Referred Offset (IRO[2:0])
IRO SIGN, IRO[2:0]INPUT-REFERRED OFFSET
CORRECTION AS % OF VDD
INPUT-REFERRED OFFSET, CORRECTION
AT VDD = 5VDC IN mV1,111+1.25+63
1,110+1.08+54
1,101+0.90+45
1,100+0.72+36
1,011+0.54+27
1,010+0.36+18
1,001+0.18+9
1,00000
0,00000
0,001-0.18-9
0,010-0.36-18
0,011-0.54-27
0,100-0.72-36
0,101-0.90-45
0,110-1.08-54
0,111-1.25-63
MAX1455Low-Cost Precision Sensor Signal Conditioner
