Low-Cost Automotive Sensor Signal Conditioner Provides Amplificat

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Low-Cost Automotive Sensor Signal Conditioner Provides Amplificat

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19-2088; 10/01
Low-Cost Automotive Sensor Signal Conditioner
Provides Amplification, Calibration, Temperature Compensation Selectable Output Clipping Limits Accommodates Sensor Output Sensitivities from 5mV/V 40mV/V Single-Pin Digital Programming External Trim Components Required 16-Bit Offset Span Calibration Resolution Fully Analog Signal Path Bridge Used TemperatureCorrection Input On-Chip Lookup Table Supports Multipoint Calibration Temperature Correction Fast 3.2kHz Frequency Response On-Chip Uncommitted Secure-LockPrevents Data Corruption
MAX1455
MAX1455 highly integrated automotive analogsensor signal processor resistive element sensors. MAX1455 provides amplification, calibration, temperature compensation that enable overall performance approaching inherent repeatability sensor. fully analog signal path introduces quantization noise output signal while enabling digitally controlled trimming with integrated 16-bit digital-to-analog converters (DACs). Offset span also calibrated using 16-bit DACs, allowing sensor products truly interchangeable. MAX1455 architecture includes programmable sensor excitation, 16-step programmable-gain amplifier (PGA), 768-byte (6144 bits) internal EEPROM, four 16-bit DACs, uncommitted amp, onchip temperature sensor. addition offset span compensation, MAX1455 provides unique temperature compensation strategy that developed provide remarkable degree flexibility while minimizing testing costs. MAX1455 available form, 16-pin SSOP TSSOP packages.
Customization
Maxim customize MAX1455 high-volume dedicated applications. Using dedicated cell library more than 2000 sensor-specific function blocks, Maxim quickly provide modified MAX1455 solution. Contact Maxim further information.
PART MAX1455EUE* MAX1455AUE* MAX1455EAE MAX1455AAE
Ordering Information
TEMP. RANGE -40°C +85°C -40°C +125°C -40°C +85°C -40°C +125°C PIN-PACKAGE TSSOP TSSOP SSOP SSOP
Applications
Pressure Sensors Transducers Piezoresistive Silicon Sensors Strain Gauges Resistive Element Sensors Accelerometers Humidity Sensors Sensors
MAX1455C/D -40°C +85°C Dice** *Future product-contact factory availability.
**Dice tested +25°C, parameters only.
Configuration
VIEW
TEST1 TEST2 TEST3 TEST4 MAX1455 UNLOCK VDD2 AMP9 AMPOUT
Outputs
Ratiometric Voltage Output Programmable Output Clip Limits
detailed Functional Diagram appears data sheet. Secure-Lock trademark Maxim Integrated Products, Inc.
VDD1 AMP+
SSOP/TSSOP
Maxim Integrated Products
pricing, delivery, ordering information, please contact Maxim/Dallas Direct! 1-888-629-4642, visit Maxim's website www.maxim-ic.com.
Low-Cost Automotive Sensor Signal Conditioner MAX1455
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, VDD_ .-0.3V, VDD1 VDD2 .-0.3V, +0.6V Other Pins.(VSS 0.3V) (VDD_ 0.3V) Short-Circuit Duration, OUT, BDR, AMPOUT .Continuous Continuous Power Dissipation +70°C) 16-Pin SSOP (derate 8.00mW/°C above +70°C) .640mW Operating Temperature Ranges (TMIN TMAX) MAX1455EUE .-40°C +85°C MAX1455AUE .-40°C +125°C MAX1455C/D .-40°C +85°C MAX1455EAE .-40°C +85°C MAX1455AAE .-40°C +125°C Storage Temperature Range .-65°C +150°C Lead Temperature (soldering, 10s) +300°C
Stresses beyond those listed under "Absolute Maximum Ratings" cause permanent damage device. These stress ratings only, functional operation device these other conditions beyond those indicated operational sections specifications implied. Exposure absolute maximum rating conditions extended periods affect device reliability.
ELECTRICAL CHARACTERISTICS
(VDD +5V, +25°C, unless otherwise noted.)
PARAMETER GENERAL CHARACTERISTICS Supply Voltage Supply Current Oscillator Frequency ANALOG INPUT Input Impedance Input-Referred Adjustable Offset Range Input-Referred Offset Tempco Amplifier Gain Nonlinearity Common-Mode Rejection Ratio Minimum Input-Referred Range Maximum Input-Referred Range ANALOG OUTPUT Minimum Differential SignalGain Range Maximum Differential SignalGain Range [3:0] 0000 [3:0] 1111 Clip[1:0] Clip[1:0] Clip[1:0] Clip[1:0] Load Current Source High High High High 0.10 4.90 0.15 4.85 0.20 4.80 0.25 4.75 CMRR Specified common-mode voltages between (Note (Note Offset (Note minimum gain TMIN TMAX ±150 0.025 µV/°C mV/V mV/V fOSC IDD1 IDD2 (Note 0.85 1.15 SYMBOL CONDITIONS UNITS
Output Clip Voltage Settings
VOUT
load, TMIN TMAX
VOUT +0.5V +4.5V, TMIN TMAX, Clip[1:0]
Low-Cost Automotive Sensor Signal Conditioner
ELECTRICAL CHARACTERISTICS (continued)
(VDD +5V, +25°C, unless otherwise noted.)
PARAMETER Load Current Sink Output Impedance Offset Output Ratio Offset Output Ratio Step Response Output Capacitive Load Output Noise BRIDGE DRIVE Bridge Current Current Mirror Ratio Minimum FSODAC Code DIGITAL-TO-ANALOG CONVERTERS Resolution ODAC Weight OTCDAC Weight FSODAC Weight FSOTCDAC Weight COARSE-OFFSET IRODAC Resolution IRODAC Weight INTERNAL RESISTORS Current-Source Reference Full-Span Output (FSO) Trim Resistor Resistor Temperature Coefficient Minimum Resistance Value Maximum Resistance Value Resistor Matching AUXILIARY Open-Loop Gain Input Common-Mode Range Output Swing load, TMIN TMAX 0.01 0.01 RISRC RSTC Applies RISRC RSTC Applies RISRC RSTC Applies RISRC RSTC RISRC RSTC 1333 ppm/°C Excluding sign VOUT/CODE, input referred, reference +5.0V (Note Bits mV/Bit VOUT CODE, reference +5.0V (Note VOUT CODE, reference VBDR 2.5V (Note VOUT CODE, reference +5.0V (Note VOUT CODE, reference VBDR 2.5V (Note Bits µV/Bit µV/Bit µV/Bit µV/Bit Recommended minimum value IBDR VBDR 3.75V 4000 mA/mA 1kHz (gain minimum, source impedance VOUT/ODAC VOUT/OTCDAC final value SYMBOL CONDITIONS VOUT +0.5V +4.5V, TMIN TMAX, Clip[1:0] 1000 UNITS mVRMS
MAX1455
Low-Cost Automotive Sensor Signal Conditioner MAX1455
ELECTRICAL CHARACTERISTICS (continued)
(VDD +5V, +25°C, unless otherwise noted.)
PARAMETER Output Current Drive Common-Mode Rejection Ratio Input Offset Voltage Unity-Gain Bandwidth TEMPERATURE-TO-DIGITAL CONVERTER Temperature Resolution Offset Gain Nonlinearity Lowest Digital Output Highest Digital Output EEPROM Maximum Erase/Write Cycles Erase Time (Notes (Note Cycles 1.45 Bits Bits °C/Bit CMRR SYMBOL CONDITIONS VOUT (VSS 0.25) (VDD 0.25) 2.5V unity-gain buffer (Note +25°C TMIN TMAX UNITS
Note Note Note Note Note Note Note Note
Excludes sensor load current. This maximum allowable sensor offset. This sensor's sensitivity normalized drive voltage, assuming desired full-span output bridge voltage 2.5V. weight ratiometric VDD. units production tested +25°C. Limits over temperature guaranteed design. Programming EEPROM temperatures below +70°C recommended. operation above +70°C, limit erase/write cycle 100. erase commands require 7.1ms minimum time.
Typical Operating Characteristics
(VDD_ +5V, +25°C, unless otherwise noted.)
OFFSET
MAX1455 toc01
AMPLIFIER GAIN NONLINEARITY
MAX1455 toc02
OUTPUT NOISE
SHORTED TOGETHER 0HEX
MAX1455 toc03
(mV) -0.5 -1.0 -1.5 -2.0 -2.5
OUTPUT ERROR FROM STRAIGHT LINE (mV) ODAC +6000HEX OTCDAC FSODAC 6000HEX FSOTCDAC 8000HEX 2HEX
10mV/div
-2.5
-5.0 400µs/div CODE INPUT VOLTAGE [INP INM] (mV)
Low-Cost Automotive Sensor Signal Conditioner
Description
NAME TEST1, TEST3, TEST2 VDD1 AMP+ AMPOUT AMPVDD2 UNLOCK TEST4 FUNCTION Test Pins. Connect leave unconnected. Analog Output. Internal voltage nodes accessed digital mode. parallel connected DIO. Bypass ground with 0.1µF capacitor reduce output noise. Positive Input. swapped Configuration register. Bridge Drive Output Negative Input. swapped Configuration register. Negative Supply Voltage Positive Supply Voltage Connect 0.1µF capacitor from VSS. Auxiliary Positive Input Auxiliary Output Auxiliary Negative Input Positive Supply Voltage Connect 0.47µF capacitor from VDD2 VSS. Connect VDD2 VDD1 improved noise performance, connect resistor VDD1. Secure-Lock Disable. There 150µA pulldown VSS. Connect disable Secure-Lock enable serial communication. Digital Input Output. Single-pin serial communication port. There internal pullups DIO. Connect pullup resistor from when digital mode. Test Pin. connect.
MAX1455
Detailed Description
MAX1455 provides amplification, calibration, temperature compensation enable overall performance approaching inherent repeatability sensor. fully analog signal path introduces quantization noise output signal while enabling digitally controlled trimming with integrated 16-bit DACs. MAX1455 includes four selectable high/low clipping limits discrete 50mV steps from 0.1V/4.9V 0.25V/4.75V. Offset span calibrated within ±0.02% span. MAX1455 architecture includes programmable sensor excitation, 16-step PGA, 768-byte (6144 bits) internal EEPROM, four 16-bit DACs, uncommitted amp, on-chip temperature sensor. MAX1455 also provides unique temperature compensation strategy that developed provide remarkable degree flexibility while minimizing testing costs. customer select from temperature points compensate their sensor. This allows latitude compensate sensor with simple first-order linear correction match unusual temperature curve. Programming independent 16-bit
EEPROM locations corrects performance 1.5°C temperature increments over range -40°C +125°C. sensors that exhibit characteristic temperature performance, select number calibration points used with number preset values that define temperature curve. sensor MAX1455 should same temperature during calibration use. This allows electronics sensor errors compensated together optimizes performance. applications where sensor electronics different temperatures, MAX1455 sensor bridge input correct temperature errors. single pin, serial communication architecture ability timeshare activity with sensor's output signal enables output sensing calibration programming single line parallel connecting DIO. MAX1455 provides Secure-Lock feature that allows customer prevent modification sensor coefficients 52-byte user-definable EEPROM data after sensor been calibrated. Secure-Lock feature also provides hardware override enable factory rework recalibration assertion logic high UNLOCK pin.
Low-Cost Automotive Sensor Signal Conditioner
MAX1455 allows complete calibration sensor verification performed single test station. Once calibration coefficients have been stored ASIC, customer choose retest order verify performance part regular audit generate final test data individual sensors. addition, Maxim developed pilot production test system reduce time market. Engineering test evaluation pilot production MAX1455 performed without expending cost time develop in-house test capabilities. Contact Maxim additional information. Frequency response user adjusted values lower than 3.2kHz bandwidth using uncommitted simple passive components. MAX1455 (Figure provides analog amplification path sensor signal. uses digitally controlled analog path nonlinear temperature correction. applications, analog architecture available first-order temperature correction. Calibration correction achieved varying offset gain varying sensor bridge excitation current voltage. utilizes switched capacitor CMOS technology, with input-referred offset trimming range more than ±150mV with approximate resolution bits). provides gain values from 39V/V 234V/V steps. MAX1455 uses four 16-bit DACs with calibration coefficients stored user internal EEPROM (6144 bits). This memory contains following information, 16-bit-wide words: Configuration register Offset calibration coefficient table Offset temperature coefficient register calibration coefficient table temperature correction register bytes (416 bits) uncommitted customer programming manufacturing data (e.g., serial number date)
MAX1455
BIAS GENERATOR
MAX1455
OSCILLATOR CLIP-TOP
TEST TEST TEST TEST
CURRENT SOURCE
CLIP-BOT ANAMUX
8-BIT
VDD1 VDD2 UNLOCK CONTROL
16-BIT
TEMP SENSOR
176-POINT TEMPERATUREINDEXED COEFFICIENTS 176-POINT TEMPERATUREINDEXED OFFSET COEFFICIENTS BITS USER DATA CONFIG 6144-BIT EEPROM
16-BIT OFFSET 16-BIT OFFSET 16-BIT AMPAMPOUT
AMP+
Figure Functional Diagram
Offset Correction
Initial offset correction accomplished input stage signal gain amplifiers coarse offset setting. Final offset correction occurs through temperature-indexed lookup table with hundred seventy-six 16-bit entries. on-chip temperature sensor provides unique 16-bit offset trim value from table with indexing resolution approximately 1.5°C from -40°C +125°C. Every millisecond, on-chip temperature sensor provides indexing into offset lookup table EEPROM resulting value
transferred offset register. resulting voltage into summing junction output, compensating sensor offset with resolution ±76µV (±0.0019% FSO). offset zero, then maximum temperature error equivalent temperature drift sensor, given that Offset corrected sensor every 1.5°C. temperature indexing boundaries outside specified absolute maximum ratings. minimum indexing value 00hex, corresponding approximately -69°C. temperatures below this value output coefficient value index 00hex. maximum indexing value AFhex, which highest lookup table entry. temperatures higher than approximately +184°C output highest lookup table index value. indexing wraparound errors produced.
Correction
functional blocks control gain calibration. First, coarse gain digitally selecting gain PGA. Second, FSODAC sets sensor bridge current voltage with digital input obtained from temperature indexed reference lookup table EEPROM. correction occurs through
Low-Cost Automotive Sensor Signal Conditioner
temperature indexed lookup table with hundred seventy-six 16-bit entries. on-chip temperature sensor provides unique trim from table with indexing resolution approaching 16-bit value every 1.5°C from -40°C +125°C. temperature indexing boundaries outside specified absolute maximum ratings. minimum indexing value 00hex, corresponding approximately -69°C. temperatures below this value output coefficient value index 00hex. maximum indexing value AFhex, which highest lookup table entry. temperatures higher than approximately +184°C output highest lookup table index value. indexing wraparound errors produced. changing affects offset nature bridge. temperature measured both MAX1455 bridge sensor. recommended compensate first-order temperature errors using bridge sensor temperature.
MAX1455
Typical Ratiometric Operating Circuit
Ratiometric output configuration provides output that proportional power-supply voltage. This output then applied ratiometric produce digital value independent supply voltage. Ratiometricity important consideration battery-operated instruments, automotive, some industrial applications. MAX1455 provides high-performance ratiometric output with minimum number external components (Figure These external components include following: supply bypass capacitor optional output suppression capacitor
Linear Nonlinear Temperature Compensation
Writing 16-bit calibration coefficients into offset FSOTC registers compensates first-order temperature errors. piezoresistive sensor powered current source resulting temperature-dependent bridge voltage sensor's temperature coefficient resistance (TCR). reference inputs offset FSOTC connected bridge voltage. output voltages track bridge voltage varies with temperature, varying offset FSOTC digital code portion bridge voltage, which temperature dependent, used compensate first-order temperature errors. internal feedback resistors (RISRC RSTC) temperature compensation 75k. calculate required offset FSOTC compensation coefficients, test temperatures needed. After taking least measurements each temperature, calibration software host computer) calculates correction coefficients writes them internal EEPROM. With coefficients ranging from 0000hex FFFFhex reference, each resolution 76µV. DACs (offset FSOTC) utilize sensor bridge voltage reference. Since sensor bridge voltage approximately +2.5V, FSOTC offset exhibit step size less than 38µV. high-accuracy applications (errors less than 0.25%), first-order offset FSOTC should compensated with offset FSOTC DACs, residual higher order terms with lookup table. offset compensation DACs provide unique compensation values approximately 1.5°C temperature change temperature indexes address pointer through coefficient lookup table. Changing offset does affect FSO; however,
Typical Nonratiometric Operating Circuit (5.5VDC VPWR 28VDC)
Nonratiometric output configuration enables sensor power vary over wide range. low-dropout voltage regulator, such MAX1615, incorporated circuit provide stable supply reference MAX1455 operation. typical example shown Figure Nonratiometric operation valuable when wide ranges input voltage expected system readout device does enable ratiometric operation.
Internal Calibration Registers
MAX1455 five 16-bit internal calibration registers (ICRs) that loaded from EEPROM, loaded from serial digital interface. Data loaded into ICRs under three different circumstances. Normal Operation, Power-On Initialization Sequence: MAX1455 been calibrated, SecureLock byte (CL[7:0] FFhex), UNLOCK low. Power applied device. power-on reset (POR) functions have been completed. Registers CONFIG, OTCDAC, FSOTCDAC refreshed from EEPROM.
Low-Cost Automotive Sensor Signal Conditioner MAX1455
VDD1 MAX1455 VDD2
SENSOR
0.1µF
0.1µF
Figure Basic Ratiometric Output Configuration
MAX1615 SHDN VPWR +5.5V +28V
VDD1 MAX1455 VDD2
SENSOR
0.47µF 0.1µF
0.1µF
0.1µF
Figure Basic Nonratiometric Output Configuration
Registers ODAC FSODAC refreshed from temperature indexed EEPROM locations.
Registers ODAC FSODAC refreshed from temperature indexed EEPROM locations.
Normal Operation, Continuous Refresh: MAX1455 been calibrated, SecureLock byte been (CL[7:0] FFhex), UNLOCK low. Power applied device. functions have been completed. temperature index timer reaches time period. Registers CONFIG, OTCDAC, FSOTCDAC refreshed from EEPROM.
Calibration Operation, Registers Updated Serial Communications: MAX1455 Secure-Lock byte (CL[7:0] 00hex) UNLOCK high. Power applied device. functions have been completed. registers then loaded from serial digital interface serial commands. section serial commands.
Low-Cost Precision Sensor Signal Conditioner
Internal EEPROM
internal EEPROM organized 8-bit memory. divided into pages, with bytes page. Each page individually erased. memory structure arranged shown Table look-up tables ODAC FSODAC also shown, with respective temperature index pointer. Note that ODAC table occupies continuous segment, from address 000hex address 15Fhex, whereas FSODAC table divided parts, from 200hex 2FFhex, from 1A0hex 1FFhex. With exception general-purpose user bytes, values 16-bitwide words formed adjacent byte locations (high byte byte). MAX1455 compensates sensor offset, FSO, temperature errors loading internal calibration registers with compensation values. These compensation values loaded registers directly through serial digital interface during calibration loaded automatically from EEPROM power-on. this way, device tested configured during calibration test appropriate compensation values stored internal EEPROM. device autoloads registers from EEPROM ready without further configuration after each power-up. EEPROM configured 8-bit-wide array each 16-bit registers stored 8-bit quantities. Configuration register, FSOTCDAC, OTCDAC registers loaded from preassigned locations EEPROM. Table EEPROM ODAC FSODAC lookup table memory map. ODAC FSODAC loaded from EEPROM lookup tables using index pointer that function temperature. converts integrated temperature sensor 8-bit value every 1ms. This digitized value then transferred into Temp-Index register. Table lists registers. typical transfer function temp-index follows: temp-index 0.69 Temperature (°C) 47.58 where temp-index truncated 8-bit integer value. Typical values Temp-Index register given Table Note that EEPROM byte wide registers that loaded from EEPROM bits wide. Thus, each index value points bytes EEPROM. Maxim programs EEPROM locations FFhex with exception oscillator frequency setting Secure-Lock byte. OSC[2:0] Configuration register (Table These bits should maintained factory-preset values. Programming 00hex Secure-Lock byte (CL[7:0] 00hex) configures asynchronous serial input calibration test purposes.
MAX1455
MAX1455 Digital Mode
single-pin serial interface provided accesses MAX1455's control functions memory. command inputs this flow into registers, which form interface register (IRS). Additional levels command processing provided control logic, which takes inputs from IRS. bidirectional 16-bit latch buffers data from 16-bit Calibration registers internal (8-bit-wide) EEPROM locations. Figure shows relationship between various serial commands MAX1455 internal architecture.
Communication Protocol
serial interface used asynchronous serial data communications between MAX1455 host calibration test system computer. MAX1455 automatically detects baud rate host computer when host transmits initialization sequence. Baud rates between 4800 38400 detected used. data format always start bit, data bits, stop bit. data bits transmitted first, last. weak pullup resistor used maintain logic while MAX1455 digital mode. This prevent unintended transitions this pin, which would interpreted communication start bit. Communications only allowed when Secure-Lock byte disabled (i.e., CL[7:0] 00HEX UNLOCK held high. Table control location.
Initialization Sequence
first Command Byte sent MAX1455 after power-up, following receipt reinitialization command, used MAX1455 learn communication baud rate. initialization sequence 1byte transmission hex, follows:
start bit, shown bold above, initiates baud rate synchronization. data bits 01hex (LSB first) follow this then stop bit, also shown bold above. MAX1455 uses this sequence calculate time interval 1-bit transmission multiple period internal oscillator. resulting number oscillator clock cycles then stored internally 8-bit number (BITCLK). Note that device power supply should stable minimum period before initialization sequence sent. This allows time function complete configured Secure-Lock byte UNLOCK.
Low-Cost Automotive Sensor Signal Conditioner MAX1455
Table EEPROM Memory Address
PAGE LOW-BYTE ADDRESS (hex) HIGH-BYTE ADDRESS (hex) FSODAC Lookup Table General-Purpose User Bytes TEMP-INDEX[7:0] (hex) Configuration Reserved OTCDAC Reserved FSOTCDAC Control Location ODAC Lookup Table CONTENTS
Low-Cost Automotive Sensor Signal Conditioner
Table EEPROM ODAC FSODAC Lookup Table Memory
TEMP-INDEX[7:0] 00hex 7Fhex 80hex AFhex EEPROM ADDRESS ODAC BYTE HIGH BYTE 000hex 001hex 0FEhex 0FFhex 100hex 101hex 15Ehex 15Fhex EEPROM ADDRESS FSODAC BYTE HIGH BYTE 200hex 201hex 2FEhex 2FFhex 1A0hex 1A1hex 1FEhex 1FFhex
MAX1455
Table Registers
REGISTER CONFIG ODAC OTCDAC FSODAC FSOTCDAC Configuration register Offset register Offset temperature coefficient register Full-span output register Full-span output temperature coefficient register DESCRIPTION
Table Temp-Index Typical Values
TEMPERATURE (°C) +125 TEMP-INDEX[7:0] DECIMAL HEXADECIMAL
Reinitialization Sequence
MAX1455 provides reestablishing, relearning, baud rate. reinitialization sequence 1-byte transmission FFhex, follows:
When serial reinitialization sequence received, receive logic resets itself power-up state waits initialization sequence. initialization sequence must follow reinitialization sequence order reestablish baud rate.
WEAK PULLUP REQUIRED
WEAK PULLUP REQUIRED
DATA
000001
XXXX
RECEIVE
TRANSMIT
HIGH-Z
RECEIVE
HOST
TRANSMIT
HIGH-Z
RECEIVE
HIGH-Z
TRANSMIT
Figure Output Data Format
Low-Cost Automotive Sensor Signal Conditioner MAX1455
Table Configuration Register (CONFIG[15:0])
FIELD 15:13 12:11 NAME OSC[2:0] CLIP[1:0] Sign Sign IRO[2:0] PGA[3:0] ODAC Sign OTCDAC Sign DESCRIPTION Oscillator frequency setting. Factory preset; change. Sets output clip levels. Logic inverts polarity (Table Logic positive input-referred offset (IRO). Logic negative IRO. Input-referred coarse-offset adjustment (Table Programmable-gain amplifier setting. Logic positive offset output. Logic negative offset output. Logic positive offset output. Logic negative offset output.
Table Gain Setting (PGA[3:0])
PGA[3:0] 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111 GAIN (V/V)
contents comprises 4-bit interface register address (IRSA) nibble 4-bit interface register data (IRSD) nibble. Command Byte structured follows: IRS[7:0] IRSD[3:0], IRSA[3:0] commands transmitted first. first following start IRSA[0] last before stop IRSD[3] follows:
IRSA IRSD
Half register contents used data hold steering information. Data writes locations within cause immediate action (command execution). These locations addresses Command Register Internal Logic (CRIL) reinitialize commands, respectively. Table shows full listing address decoding. Command sequences written MAX1455 continuous stream, i.e., start bit, command byte, stop bit, start bit, command byte, stop bit, etc. There delay requirements between commands while MAX1455 receiving data.
Command Register Internal Logic
data write CRIL location (IRS address causes immediate execution command associated with 4-bit data nibble written. EEPROM Calibration register read write, together with EEPROM erase, commands handled through CRIL location. CRIL also used enable MAX1455 analog output place output data (serial digital output) DIO. Table shows full listing CRIL commands.
Serial Interface Command Format
communication commands into MAX1455 follow format start bit, command bits (command byte), stop bit. Command Byte controls
Low-Cost Automotive Sensor Signal Conditioner MAX1455
Table Input Referred Offset (IRO[2:0])
SIGN, IRO[2:0] 1,111 1,110 1,101 1,100 1,011 1,010 1,001 1,000 0,000 0,001 0,010 0,011 0,100 0,101 0,110 0,111 INPUT-REFERRED OFFSET CORRECTION +1.25 +1.08 +0.90 +0.72 +0.54 +0.36 +0.18 -0.18 -0.36 -0.54 -0.72 -0.90 -1.08 -1.25 INPUT-REFERRED OFFSET, CORRECTION 5VDC
Serial Digital Output
configured digital output writing Read (RDIRS) command hex) CRIL location. receipt this command, MAX1455 outputs byte data, contents which determined pointer (IRSP[3:0]) value location IRSA[3:0] 8hex. data output single byte, framed start stop bit. Table lists data returned each IRSP address value. Once RDIRS command been sent, connections must three-stated allow MAX1455 drive line. Following receipt RDIRS command, MAX1455 drives high after byte time. MAX1455 holds high single time then asserts start (drives low). start then followed data byte stop bit. Immediately following transmission stop bit, MAX1455 three-states DIO, releasing line. MAX1455 then ready receive next command sequence byte time after release DIO.
Note that there time intervals before after MAX1455 sends data byte when devices line three-stated. recommended that weak pullup resistor applied line during these time intervals prevent unwanted transitions (Figure applications where analog output (OUT) connected, pullup resistor should permanently connected DIO. MAX1455 analog outputs connected, then load this common line during analog measurements. this situation, perform following sequence: Connect pullup resistor DIO/OUT line, preferably with relay. Send RDIRS command. Three-state user connection (set high impedance). Receive data from MAX1455. Activate user connection (pull DIO/OUT line high). Release pullup resistor.
Low-Cost Automotive Sensor Signal Conditioner MAX1455
COMMAND BITS) IRSA [3:0] IRSD [3:0] [3:0] 0000 0001 [7:4] 0010 [11:8] 0011 [15:12] 0100 RESERVED 0101 RESERVED ICRA [3:0] 0110 IEEA [3:0] 0111 IEEA [7:4] IRSP [3:0] 1000 IEEA [9:8] CRIL [3.0] 1001 (EXECUTE) 1010 ATIM [3:0] 1011 ALOC [3:0] 1100 RESERVED 1110 RELEARN 1111 BAUD RATE TABLE INTERFACE REGISTER COMMANDS
BIDIRECTIONAL 16-BIT DATA LATCH
[7:0] [15:8]
ICRA [3:0] CALIBRATION REGISTER CONFIG 0000 0001 ODAC 0010 OTCDAC 0011 FSODAC 0100 FSOTCDAC 0101 RESERVED 1111 TABLE INTERNAL CALIBRATION REGISTERS CRIL [3:0] FUNCTION LOAD 0000 0001 WRITE EEPROM 0010 ERASE EEPROM 0011 READ 0100 READ EEPROM READ 0101 0110 ANALOG 0111 ERASE PAGE 1000 RESERVED 1111 TABLE CRIL ACTIONS
EEPROM MEMORY BITS
ADDR
DATA
LOOKUP ADDRESS TEMP INDEX [7:0] ENABLE ANALOG OUTPUT
OUTPUT TIMER
IRSP [3:0] RETURNS [7:0] 0000 0001 [F:8] 0010 IEEA [7:4], ICRA [3:0] 0011 CRIL [3:0], IRSP [3:0] 0100 ALOC [3:0], ATIM [3.0] IEEA [7:0] 0101 0110 IEED [7:0] 0111 TEMP-INDEX [7:0] BITCLK [7:0] 1000 1001 RESERVED 1010 11001010 (USE 1111 CHECK COMMUNICATION) TABLE POINTER FUNCTIONS (READS)
OUTPUT
Figure MAX1455 Serial Command Structure Hardware Schematic
Figure shows example transmit/receive sequence with RDIRS command (59hex) being sent MAX1455 responding with byte value 10hex.
Internal Clock Settings
Following initial power-up, after power reset, calibration registers within MAX1455 contain 0000hex must programmed. Note that analog
mode, internal registers automatically refreshed from EEPROM. When starting MAX1455 digital mode, special attention bits: 3MSBs Configuration register. frequency MAX1455 internal oscillator measured during production testing 3-bit adjustment (calibration) code calculated
Low-Cost Automotive Sensor Signal Conditioner MAX1455
Table Control Location (CL[15:0])
FIELD 15:8 NAME CL[15:8] CL[7:0] Reserved Control Location. Secure-Lock activated setting this FFhex, which disables serial communications connects output. DESCRIPTION
Table IRSA Decoding
IRSA[3:0] 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1110 1111 DESCRIPTION Write IRSD[3:0] DHR[3:0] (Data Hold register) Write IRSD[3:0] DHR[7:4] (Data Hold register) Write IRSD[3:0] DHR[11:8] (Data Hold register) Write IRSD[3:0] DHR[15:12] (Data Hold register) Reserved Reserved Write IRSD[3:0] ICRA[3:0] IEEA[3:0] (Internal Calibration register address internal EEPROM address nibble Write IRSD[3:0] IEEA[7:4] (internal EEPROM address, nibble Write IRSD[3:0] IRSP[3:0] IEEA[9:8] (Interface register pointer where IRSP[1:0] IEEA[9:8]) Write IRSD[3:0] CRIL[3:0] (Command register internal logic) Write IRSD[3:0] ATIM[3:0] (analog timeout value read) Write IRSD[3:0] ALOC[3:0] (analog location) Reserved Write IRSD[3:0] 1111bin relearn baud rate
stored upper bits EEPROM location 161hex (EEPROM upper configuration byte). MAX1455 internal clock controls timing functions, including signal path gain, functions, communications. recommended that, while digital mode, Configuration register bits assigned values contained EEPROM (upper configuration byte). bits represent two's-complement number with nominal clock adjustment bit. Table shows codes adjustment available. change values contained Configuration register must followed MAX1455 baud rate learning sequence (reinitialize initialize commands). maximize robustness communication system during clock resetting only, change bits 1LSB value time. rec-
ommended setting procedure Configuration register bits therefore, follows. (Use minimum baud rate 9600 during setting procedure prevent potential overflow MAX1455 baud rate counter with clock values near maximum.) following example based required code binary: Read bits (3MSBs) from EEPROM location 161hex. binary. bits Configuration register binary. Send reinitialize command, followed initialize (baud rate learning) command. bits Configuration register binary.
Low-Cost Automotive Sensor Signal Conditioner MAX1455
Table CRIL Command Codes
CRIL[3:0] 0000 0001 0010 0011 0100 0101 0110 NAME LdICR EEPW ERASE RdICR RdEEP RdIRS RdAlg DESCRIPTION Load Internal Calibration register address given ICRA with data from DHR[15:0]. EEPROM write data bits from DHR[7:0] address location pointed IEEA [9:0]. Erase EEPROM (all bytes equal FFhex). Read Internal Calibration register pointed ICRA load data into DHR[15:0]. Read internal EEPROM location load data into DHR[7:0] pointed IEEA [9:0]. Read Interface register pointer IRSP[3:0]. Table Output multiplexed analog signal onto OUT. analog location specified ALOC[3:0] (Table duration byte times) that signal asserted onto specified ATIM[3:0] (Table 14). Erases page EEPROM pointed IEEA[9:6]. There bytes page thus pages EEPROM. Reserved.
0111 1000 1111
PageErase Reserved
Send reinitialize command, followed initialize (baud rate learning) command. frequency internal oscillator checked time reading value BITCLK[7:0]. This 8bit number represents number internal oscillator cycles corresponding cycle time) communications baud rate.
Erasing Writing EEPROM
internal EEPROM must erased (bytes FFhex) prior programming desired contents. MAX1455 supplied nominally erased state except byte 161hex byte 16Bhex. 3MSBs byte 161hex contain internal oscillator calibration setting. Byte 16Bhex 00hex allow serial communication regardless UNLOCK status. When erasing EEPROM, first save 3MSBs byte 161hex. Following erasure, these bits must rewritten, together with Secure-Lock byte value 00hex. Failure this cause part stop communicating. remove power from device before rewriting these values. internal EEPROM entirely erased with ERASE command partially erased with PageErase command (Table 10). necessary wait 7.1ms after issuing erase PageErase command. attempt communicate with part interrupt power before 7.1ms have elapsed produce indeterminate states within EEPROM.
erase page EEPROM (PageErase command): First load required page number (Table into location IEEA[3:0]. Then send CRIL PageErase command (79hex). write byte EEPROM: Load locations IEEA[9:8], IEEA[7:4], IEEA[3:0] with byte address (Address[9:0]). Load locations DHR[7:4] DHR[3:0] with data bits written (Data[7:0]). Send EEPROM WRITE command CRIL (19hex). read byte from EEPROM: Load locations IEEA[9:8], IEEA[7:4], IEEA[3:0] with byte address (Address[9:0]). Send READ EEPROM command CRIL register (49hex); this loads required EEPROM byte into DHR[7:0]. Load location IRSP[3:0] with 00hex (return DHR[7:0]). Send READ IRSP command CRIL register (59hex).
Multiplexed Analog Output
MAX1455 provides facility output analog signals while digital mode through read analog (RdAlg) command. byte time after receiving RdAlg command, internal analog signal determined ALOC[3:0] register (Table multiplexed MAX1455 OUT. signal remains connected duration ATIM[3:0] register.
Low-Cost Automotive Sensor Signal Conditioner
Table IRSP Decode
IRSP[3:0] 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010-1111 DHR[7:0] DHR[15:8] IEEA[7:4], ICRA[3:0] concatenated CRIL[3:0], IRSP[3:0] concatenated ALOC[3:0], ATIM[3:0] concatenated IEEA[7:0] EEPROM address byte IEED[7:0] EEPROM data byte Temp-Index[7:0] BitClock[7:0] Reserved. Internal flash test data. 11001010 (CAhex). This used test communication. RETURNED VALUE
Table Code (3MSBs Configuration Register)
CODE (BIN) CLOCK ADJUSTMENT
MAX1455 three-state duration that analog output active. This allow connected parallel. When connected parallel, host computer must also three-state communications connection MAX1455. This requirement produces periods when connections three-stated simultaneously, making necessary have weak pullup resistor applied during these periods. continuous output mode available analog output selected setting ATIM[3:0] Fhex. This mode only used when separate. While this mode following receipt RdAlg command, other command, three-states period 32,769 byte times. Once this period elapsed, enters receive mode accepts further command inputs. analog output always active while continuous mode. Note: internal analog signals buffered when connected OUT. loading while these internal signals being measured likely produce measurement errors. load when reading internal signals such BDR, FSOTC, etc.
MAX1455
Communication Command Examples
selection examples command sequences various functions within MAX1455 follows. Example Change baud rate setting check communications. communication with MAX1455 lost system baud rate change before sending reinitialization command, apply power reset guarantee initialization condition.
COMMAND FFhex 01hex ACTION Reinitialize part ready baud rate learning. Change system baud rate value. Learn baud rate. Load (Fhex) IRSP[3:0] register. Read IRS. Host computer must ready receive data serial line within (baud rate) byte time sending Read command. MAX1455 returns CAhex. (IRSP values configured return CAhex communication checking purposes.) F8hex 59hex
ATIM function uses communication baud rate timing basis. Table details. period determined ATIM[3:0], analog signal disconnected from analog output resumes three-state condition. MAX1455 receive further commands byte after resuming three-state condition OUT. Figure shows timing this scheme.
Low-Cost Automotive Sensor Signal Conditioner MAX1455
Example Read lookup table pointer (TempIndex).
COMMAND 78hex 59hex Read IRS. Host ready receive data within byte time sending Read command. MAX1455 returns current Temp-Index pointer value. ACTION Load IRSP[3:0] register.
Example Write 8C40hex FSODAC register.
COMMAND 00hex 41hex C2hex 83hex 36hex 09hex ACTION Load DHR[3:0] register. Load DHR[7:4] register. Load DHR[11:8] register. Load DHR[15:12] register. Load (FSODAC) ICRA[3:0] register. ICR. 8C40 written FSODAC register.
Example Enable measurement 3.4s duration with 9600 baud rate.
COMMAND 1Bhex CAhex 69hex ACTION Load (BDR measurement) ALOC[3:0] register. Load ATIM[3:0] register: (212+1) 8/9600 3.4s. RdAlg. three-stated connected internally duration approximately 3.4s.
Example Write 8C40hex FSODAC lookup table location Temp-Index This example uses Page Erase command clear relevant section EEPROM assumes that none existing data that section required kept.
COMMAND A6hex 79hex ACTION Load Ahex (page number corresponding EEPROM locations 280hex 281hex) IEEA[3:0] register. Page Erase command. Wait 7.1ms before sending further commands. 06hex 87hex 28hex 00hex 41hex Load 0hex IEEA[3:0] register. Load 8hex IEEA[7:4] register. Load 2hex IEEA[9:8] (IRSP[3:0]) register. Load 0hex DHR[3:0] register. Load 4hex DHR[7:4] register. Write EEPROM. 40hex loaded EEPROM address 280hex, which byte location corresponding Temp-Index pointer value Load IEEA[3:0] register. IEEA[7:4] IEEA[9:8] already contain respectively. Load Chex DHR[3:0] register. Load 8hex DHR[7:4] register. Write EEPROM. 8Chex loaded EEPROM address 281hex, which high byte location corresponding TempIndex pointer value
19hex
16hex C0hex 81hex
19hex
Low-Cost Automotive Sensor Signal Conditioner MAX1455
Table ALOC Definition
ALOC[3:0] 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111 ANALOG SIGNAL ISRC CLIP-TOP CLIP-BOTTOM FSODAC FSOTCDAC ODAC OTCDAC VREF VPTATP VPTAINP Output Bridge Drive Bridge Drive Current Setting Internal Positive Supply Internal Ground Clip Voltage High Value Clip Voltage Value Full-Scale Output Full-Scale Output Offset Offset Bandgap Reference Voltage (nominally 1.25V) Internal Test Node Internal Test Node Sensor's Positive Input Sensor's Negative Input DESCRIPTION
WEAK PULLUP REQUIRED
2ATIM BYTE TIMES
WEAK PULLUP REQUIRED
DATA
HIGH-Z
XXXX
XXXX
VALID OUTPUT
HIGH-Z
RECEIVE
HIGH-Z
RECEIVE
HOST
TRANSMIT
HIGH-Z
TRANSMIT
Figure Analog Output Timing
Low-Cost Automotive Sensor Signal Conditioner MAX1455
Table ATIM Definition
ATIM[3:0] 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111
DURATION ANALOG SIGNAL SPECIFIED BYTE TIMES (8-BIT TIME) byte times, i.e., baud rate byte times byte times byte times byte times byte times byte times byte times byte times byte times 1025 byte times 2049 byte times 4097 byte times 8193 byte times 16,385 byte times this mode, continuous; however, accepts commands after 32,769 byte times. parallel connect OUT.
Table ICRA Decode
ICRA[3:0] 0000 0001 0010 0011 0100 0101 0110 1111 NAME CONFIG ODAC OTCDAC FSODAC FSOTCDAC Configuration register Offset register Offset temperature coefficient register Full-scale output register Full-scale output temperature coefficient register Reserved. write this location (EEPROM test). Reserved. write this location. DESCRIPTION
Sensor Compensation Overview
Compensation requires examination sensor performance over operating pressure temperature range. minimum test pressures (e.g.,
zero full span) temperatures. More test pressures temperatures result greater accuracy. typical compensation procedure summarized follows:
Low-Cost Automotive Sensor Signal Conditioner MAX1455
DIGITAL MULTIPLEXER DIO[1:N] DIO1 DIO2 DION
MODULE
MODULE
MODULE
MAX1455
MAX1455
DATA VOUT
DATA VOUT VOUT
VOUT TEST OVEN
Figure Automated Test System Concept
Table Effects Compensation
TYPICAL UNCOMPENSATED INPUT (SENSOR) Offset.±100% FSO.1mV/V 40mV/V Offset TC.20% Offset Nonlinearity.4% FSOTC.-20% FSOTC Nonlinearity.5% Temperature Range.-40°C +125°C TYPICAL COMPENSATED TRANSDUCER OUTPUT OUT.Ratiometric 5.0V Offset +25°C.0.500V 200µV +25°C.4.000V 200µV Offset Accuracy over Temp. Range.±4mV (±0.1% FSO) Accuracy over Temp. Range.±4mV (±0.1% FSO)
Reference Temperature (e.g., 25°C): Initialize each transducer loading respective register with default coefficients (e.g., based mean values offset, FSO, bridge resistance) prevent overload MAX1455. internal calibration registers addressed ICRA[3:0] decoded shown Table initial bridge voltage (with FSODAC) half supply voltage. Measure bridge voltage using pins, calculate based measurements.
Calibrate output offset transducer using ODAC FSODAC, respectively. Store calibration data test computer MAX1455 EEPROM user memory. Calibrate offset using ODAC FSODAC, respectively. Store calibration data test computer MAX1455 EEPROM user memory. Calculate correction coefficients.
Next Test Temperature:
MAX1455
Low-Cost Automotive Sensor Signal Conditioner MAX1455
SENSOR OUTPUT +25°C)
ERROR FSO)
VOUT (mV)
UNCOMPENSATED SENSOR TEMPERATURE ERROR
OFFSET
TEMPERATURE (°C)
PRESSURE (kps)
COMPENSATED TRANSDUCER ERROR
ERROR FSO) 0.15 0.10 0.05 -0.05 -0.10 -0.15 TEMPERATURE (°C) OFFSET VOUT
COMPENSATED TRANSDUCER +25°C)
PRESSURE (kps)
Figure Comparison Uncalibrated Sensor Calibrated Transducer
Download correction coefficients EEPROM. Perform final test.
MAX1455 evaluation kit). First-time users MAX1455 strongly encouraged this kit. designed facilitate manual programming MAX1455 with sensor. includes following: Evaluation board with without silicon pressure sensor, ready customer evaluation. Design/applications manual. This manual developed test engineers familiar with data acquisition sensor data provides sensor compensation algorithms test procedures. MAX1455 communication software, which enables programming MAX1455 from computer keyboard (IBM compatible), module time. Interface adapter, which allows connection evaluation board serial port.
Sensor Calibration Compensation Example
MAX1455 temperature compensation design corrects both sensor temperature errors. This enables MAX1455 provide temperature compensation approaching inherent repeatability sensor. example MAX1455's capabilities shown Figure Table lists effects compensation. MAX1455 repeatable piezoresistive sensor with initial offset 16.4mV span 55.8mV were converted into compensated transducer with offset 0.5000V span 4.0000V. Nonlinear sensor offset temperature errors, which were order FSO, were reduced under ±0.1% FSO. Figure shows output uncompensated sensor output compensated transducer. temperature points were used obtain this result.
Chip Information
TRANSISTOR COUNT: 62,242 PROCESS: CMOS SUBSTRATE CONNECTED
MAX1455 Evaluation
expedite development MAX1455-based transducers test systems, Maxim produced
Low-Cost Automotive Sensor Signal Conditioner
Detailed Functional Diagram
MAX1455
TEST TEST TEST TEST
EEPROM (LOOKUP PLUS CONFIGURATION DATA) EEPROM ADDRESS 000H 001H 15EH 15FH 160H 161H 162H 163H 164H 165H 166H 167H 168H 169H 16AH 16BH 16CH 16DH 19EH 19FH 1A0H 1A1H BANDGAP TEMP SENSOR 2FEH 2FFH 8-BIT LOOKUP ADDRESS UNLOCK FSOTC REGISTER BANDWIDTH 3kHz ±10% DIGITAL INTERFACE CLIP-HIGH LOOKUP TABLE (176 BITS) VDD2 USAGE OFFSET LOOKUP TABLE (176 BITS) VDD1
RISRC RSTC OFFSET
CONFIGURATION REGISTER SHADOW RESERVED OFFSET REGISTER SHADOW RESERVED FSOTC REGISTER SHADOW CONTROL LOCATION REGISTER USER STORAGE BYTES)
FSOTC PHASE REVERSAL INPUT-REFERRED OFFSET (COARSE OFFSET) 2:0) OFFSET (mV) 1,111 1,110 1,101 1,100 1,011 1,010 1,001 1,000 0,000 0,001 0,010 0,011 0,100 0,101 0,110 0,111
CLIP-LOW
AMPPROGRAMMABLE GAIN STAGE (3:0) 0000 0001 0010 OFFSET REGISTER 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111 GAIN TOTAL GAIN AMPOUT
AMP+
UNCOMMITTED PARAMETER RANGE OFFSET RANGE LOAD LOAD UNITY VALUE ±20mV VSS, ±0.01V VSS, ±0.25V 10MHz TYPICAL
*INPUT-REFERRED OFFSET VALUE PROPORTIONAL VDD. VALUES GIVEN +5V.
BANDWIDTH 3kHz ±10%
Low-Cost Automotive Sensor Signal Conditioner MAX1455
Package Information
SSOP.EPS
Low-Cost Automotive Sensor Signal Conditioner
Package Information (continued)
TSSOP,NO PADS.EPS
MAX1455
Maxim cannot assume responsibility circuitry other than circuitry entirely embodied Maxim product. circuit patent licenses implied. Maxim reserves right change circuitry specifications without notice time.
Maxim Integrated Products, Gabriel Drive, Sunnyvale, 94086 408-737-7600 2001 Maxim Integrated Products Printed registered trademark Maxim Integrated Products.

Low-Cost Automotive Sensor Signal Conditioner Provides Amplificat

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