Low-Power, 16-Bit Smart Low-Noise, 400µA Single-Chip Sensor Signa

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Low-Power, 16-Bit Smart Low-Noise, 400µA Single-Chip Sensor Signa

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Low-Power, 16-Bit Smart
Low-Noise, 400µA Single-Chip Sensor Signal Conditioning High-Precision Front Resolves Less than Differential Input Signal On-Chip EEPROM Provide Digital Correction Sensor Errors 16-Bit Signal Path Compensates Sensor Offset Sensitivity Associated Temperature Coefficients 12-Bit Parallel Digital Output Analog Output Compensates Wide Range Sensor Sensitivity Offset Single-Shot Automated Compensation Algorithm-No Iteration Required Built-In Temperature Sensor Three-State, 5-Wire Serial Interface Supports High-Volume Manufacturing
MAX1460
MAX1460 implements revolutionary concept signal conditioning, where output 16-bit analog-to-digital converter (ADC) digitally corrected over specified temperature range. This feature readily exploited automotive, industrial, medical market segments, applications such sensors smart batteries. Digital correction provided internal digital signal processor (DSP) on-chip 128bit EEPROM containing user-programmed calibration coefficients. conditioned output available 12-bit digital word ratiometric (proportional supply voltage) analog voltage using on-board 12-bit digital-to-analog converter (DAC). uncommitted used filter analog output, implement 2-wire, 4-20mA transmitter. analog front includes 2-bit programmablegain amplifier (PGA) 3-bit coarse-offset (CO) DAC, which condition sensor's output. This coarsely corrected signal digitized 16-bit ADC. uses digitized sensor signal, temperature sensor, correction coefficients stored internal EEPROM produce conditioned output. Multiple batch manufacturing sensors supported with completely digital test interface. Built-in testability features MAX1460 result integration three traditional sensor-manufacturing operations into automated process: Pretest: Data acquisition sensor performance under control host test computer. Calibration Compensation: Computation storage calibration compensation coefficients determined from transducer pretest data. Final Test Operation: Verification transducer calibration compensation, without removal from pretest socket. MAX1460 evaluation kit) allows fast evaluation prototyping, using piezoresistive transducer (PRT) Windows®-based user-friendly simplifies small-volume prototyping; necessary fully understand test-system interface, calibration algorithm, many other details evaluate MAX1460 with particular sensor. Simply plug into kit, plug into parallel port, connect sensor excitation source (such pressure controller), MAX1460 software. oven required thermal compensation.
_Applications
Hand-Held Instruments Piezoresistive Pressure Acceleration Transducers Transmitters Industrial Pressure Sensors 4-20mA Transmitters Smart Battery Charge Systems Weigh Scales Strain-Gauge Measurement Flow Meters Dive Computers Liquid-Level Sensing Hydraulic Systems Automotive Systems
Ordering Information
PART MAX1460CCM TEMP. RANGE +70°C PIN-PACKAGE TQFP
Customization
Maxim customize MAX1460 unique requirements. With dedicated cell library more than sensor-specific functional blocks, Maxim quickly provide customized MAX1460 solutions, including customized microcode unusual sensor characteristics. Contact Maxim further information.
Functional Diagram appears data sheet. Configuration appears data sheet. Windows registered trademark Microsoft Corp.
Maxim Integrated Products
free samples latest literature: http://www.maxim-ic.com, phone 1-800-998-8800. small orders, phone 1-800-835-8769.
Low-Power, 16-Bit Smart MAX1460
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, VSS.-0.3V Other Pins .(VSS 0.3V) (VDD 0.3V) Short-Circuit Duration, Outputs .Continuous Continuous Power Dissipation +70°C) 48-Pin TQFP (derate 12.5mW/°C above +70°C ).1000mW Operating Temperature Range.0°C +70°C Storage Temperature Range .-65°C +160°C Lead Temperature (soldering, 10sec) .+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, fXIN 2MHz, TMIN TMAX, unless otherwise noted.) PARAMETER GENERAL CHARACTERISTICS Supply Voltage (Note Supply Current (Note Throughput Rate ANALOG INPUT Input Impedance Gain Temperature Coefficient (TC) Input-Referred Offset Common-Mode Rejection Ratio CMRR From gain code Gain Gain gain code gain code gain code CO-DAC code CO-DAC code CO-DAC code Coarse Offset CO-DAC code CO-DAC code CO-DAC code CO-DAC code CO-DAC code (Notes Resolution Integral Nonlinearity (Note Input-Referred Noise Output-Referred Noise TEMPERATURE SENSOR (Note Resolution Linearity +70°C LSB/°C input impedance gain code CO-DAC code 0.006 1700 Bits nVRMS LSBRMS -164 -111 COARSE-OFFSET (Notes -149 -134 ±1200 ppm/°C nV/°C During operation Continuous conversion 4.75 5.25 SYMBOL CONDITIONS UNITS
Low-Power, 16-Bit Smart
ELECTRICAL CHARACTERISTICS (continued)
(VDD +5V, fXIN 2MHz, TMIN TMAX, unless otherwise noted.) PARAMETER OUTPUT (Note Resolution Integral Nonlinearity Differential Nonlinearity UNCOMMITTED Supply Current Input Common-Mode Range Open-Loop Gain Offset Voltage unity-gain follower) Output Voltage Swing Output Current Range Input High Voltage Input Voltage Input Hysteresis Input Leakage Input Capacitance DIGITAL OUTPUTS: D[11.0] Output Voltage Output Voltage High Three-State Leakage Current Three-State Output Capacitance Output Voltage Output Voltage High Three-State Leakage Current Three-State Output Capacitance COUT COUT ISINK 500µA ISOURCE 500µA (Note ISINK 500µA ISOURCE 500µA (Note 50.0 50.0 VHYST (Note 50.0 2.5V load) load VOUT (VSS 0.2V) (VDD 0.2V) 0.05 ±500 0.05 bits SYMBOL CONDITIONS UNITS
MAX1460
DIGITAL INPUTS: START, CS1, CS2, SDIO (Note RESET, (Note TEST
DIGITAL OUTPUTS: SDIO (Note SDO, EOC,
Note EEPROM programming requires minimum 4.75V. exceed limits during this time. Note This value does include sensor load current. This value does include uncommitted current. Note that MAX1460 will convert continuously REPEAT MODE EEPROM. Note Analog Front-End, including PGA, Coarse Offset DAC, ADC, Temperature Sensor sections. Note signal input output plus output CO-DAC. reference VDD. plus full-scale input +VDD minus full-scale input -VDD. This specification shows contribution CO-DAC input. Note Figure outputs between +0.8500 -0.8500. Note sensor MAX1460 must always same temperature during calibration use. Note Output specified using external lowpass filter (Figure Note SDIO input/output digital pin. only enabled digital output when MAX1460 receives from test system commands (Table Note digital input only when TEST high. Note Guaranteed design. subject production testing.
Low-Power, 16-Bit Smart MAX1460
Description
41-45 NAME FUNCTION
N.C.
Connection. internally connected.
AGND START I.C. CS1,
Analog Ground. Connect using resistors (see Functional Diagram). Optional conversion start input signal, used extending sensor warm-up time. Internally pulled with (typical) resistor. Internally Connected. Leave unconnected. Parallel Digital Output Parallel Digital Output Parallel Digital Output Parallel Digital Output Parallel Digital Output Parallel Digital Output (MSB) Positive Supply Voltage Input. Connect 0.1µF bypass capacitor from VSS. Pins must connected positive power supply PCB. Negative Supply Input Chip-Select Input. MAX1460 selected when both high. When either low, digital outputs high impedance digital inputs ignored. internally pulled high with (typical) resistor. Serial Data Input/Output. Used only during programming/testing, when TEST high. test system sends commands MAX1460 through SDIO. MAX1460 returns current instruction address data being executed test system. SDIO internally pulled with (typical) resistor. SDIO goes high impedance when either remains this state until test system initiates conversion. Serial Data Output. Used only during programming/testing. allows test system monitor registers. MAX1460 returns test system results current instruction. high impedance when TEST low. Reset Input. When TEST high, low-to-high transition RESET enables MAX1460 accept commands from test system. This input ignored when TEST low. Internally pulled high with (typical) resistor. Conversion Output. high-to-low transition pulse used latch Parallel Digital Output (pins D[11.0]). Parallel Digital Output (LSB) Parallel Digital Output Parallel Digital Output
SDIO
RESET
Low-Power, 16-Bit Smart
Description (continued)
NAME AMPOUT AMP+ AMPXOUT TEST Parallel Digital Output Parallel Digital Output Parallel Digital Output Output DAC. bitstream OUT, when externally filtered, creates ratiometric analog output voltage. proportional 12-bit parallel digital output. General-Purpose Operational Amplifier Output Noninverting Input General-Purpose Operational Amplifier Inverting Input General-Purpose Operational Amplifier Internal Oscillator Output. Connect 2MHz ceramic resonator (Murata CST200) crystal from XOUT XIN. Internal Oscillator Input. When TEST high, this must driven test system with 2MHz, duty cycle clock signal. resonator does need disconnected test mode. Positive Sensor Input. Input impedance typically Rail-to-Rail® input range. Test/Program Mode Enable Input. When high, enables MAX1460 programming/testing operations. Internally pulled with (typical) resistor. Negative Sensor Input. Input impedance typically Rail-to-rail input range. FUNCTION
MAX1460
Rail-to-Rail registered trademark Nippon Motorola, Ltd.
Low-Power, 16-Bit Smart MAX1460
Detailed Description
main functions MAX1460 include: Analog Front End: Includes PGA, coarse-offset DAC, ADC, temperature sensor Test System Interface: Writes calibration coefficients registers EEPROM Test System Interface: observes operation. sensor signal enters MAX1460 adjusted coarse gain offset analog front end. Five bits configuration register coarse-offset coarse gain (Tables These bits must properly configured optimum dynamic range ADC. digitized sensor signal stored read-only register. on-chip temperature sensor also 3-bit coarse-offset that places temperature signal operating range. Digitized temperature also stored read-only register. uses digitized sensor, temperature signals, correction coefficients calculate compensated corrected output. MAX1460 supports automated production environment, where test system communicates with batch MAX1460s controls temperature sensor excitation. three-state digital outputs MAX1460 allow parallel connection transducers, that five serial interface lines (XIN, TEST, RESET, SDIO, SDO) shared. test system selects individual transducer using CS2. test system must vary sensor's input temperature, calculate correction coefficients each unit, load coefficients into MAX1460 nonvolatile EEPROM, test resulting compensation. MAX1460 implements following characteristic equation: Gain
Signal where Gain corrects sensor's sensitivity, correct Gain-TC, Signal digitized outputs analog front end, corrects sensor's offset, correct Offset-TC, DOFF output offset pedestal. test system write calibration coefficients into MAX1460 EEPROM write registers directly. MAX1460 begin conversion using either EEPROM contents register contents. When test system issues commands, MAX1460 serially controlled slave device. test system observes MAX1460 operation order acquire temperature signal results, verify calibration coefficients, output MAX1460 places contents several important registers serial interface after tester issues Start Conversion command. After calibration, compensation, final test, MAX1460 adapted sensor pair removed from test system. resulting trans-
Table Nominal Gain Settings
SETTING PGA-1 PGA-0 NOMINAL GAIN (V/V)
Table Typical Coarse Offset Settings
SETTING CO-S CO-1 CO-0 input) -149 SETTING RTI) (VDD -162 -104 SETTING RTI) (VDD -122 SETTING RTI) (VDD SETTING RTI) (VDD
Low-Power, 16-Bit Smart
ducer applying power START signal. Latch 12-bit parallel digital output using pulse. maximum conversion rate MAX1460 15Hz, using 2MHz resonator. analog output desired, build simple lowpass filter using pin, uncommitted amp, discrete components (Figure
Analog Front End, Including PGA, Coarse Offset DAC, ADC, Temperature Sensor
Before sensor signal digitized, must gained coarse-offset corrected maximize dynamic range. There bits (four possible settings) configuration register gain, bits (eight possible settings) DAC. flowchart (Figure shows procedure finding optimum
MAX1460
-MAKE TEST SYSTEM VARIABLE CALLED "NoMoreGain." -SET TEMPERATURE WHERE SENSOR'S SENSITIVITY HIGHEST. THIS NORMALLY COLD SILICON PRTs. -SET GAIN SETTINGS MINIMUM. -CLEAR VARIABLE "NoMoreGain."
-APPLY MIDSCALE EXCITATION SENSOR. -FIND COARSE OFFSET SETTING WHERE DIGITIZED SIGNAL REGISTER CLOSEST ZERO (MIDSCALE).
-APPLY MAXIMUM SENSOR EXCITATION. -TEST CLIPPING (DIGITIZED SIGNAL 0.85).
-APPLY MINIMUM SENSOR EXCITATION. -TEST CLIPPING (DIGITIZED SIGNAL -0.85).
SENSOR SENSITIVITY LARGE. RESISTOR BETWEEN SERIES BRIDGE RESISTOR THEN START OVER. CLIP? MINIMUM GAIN?
SENSOR
-REDUCE GAIN STEP. -SET VARIABLE "NoMoreGain."
MAXIMUM GAIN?
"NoMoreGain" SET?
INCREASE GAIN STEP.
RECORD COARSE OFFSET SETTINGS. CAUTION: CLIPPING STILL POSSIBLE LARGE SENSOR'S OFFSET LARGE TEMPERATURE RANGES. NECESSARY, GUARDBAND AGAINST CLIPPING REDUCING ±0.85 CLIPPING CONSTANTS ABOVE.
Figure Flowchart Determining Settings
Low-Power, 16-Bit Smart MAX1460
0.010 0.008 NONLINEARITY ERROR (%FS) 0.006 0.004 0.002 -0.002 0.004 -0.006 -0.008 -0.010 -100 SENSOR SIGNAL INPUT INPUT/OUTPUT RANGE ERROR (16-BIT LSBs)
-100 SENSOR SIGNAL INPUT INPUT RANGE
Figure Analog Front-End (typical)
Figure Analog Front-End Differential Nonlinearity (DNL) (typical)
NOISE STANDARD DEVIATION (16-BIT LSBs) -100 SENSOR SIGNAL INPUT INPUT/OUTPUT RANGE
Figure Analog Front-End Noise Standard Deviation Samples (typical)
analog front-end settings when sensor's characteristics unknown. tabulated values (Tables peak sensor excursions known. Test System Interface section details writing these analog front-end bits. gain very stable, accurate. Manufacturing variances gain offset MAX1460 analog front-end superposition residual sensor errors, later removed during final calibration. example, suppose sensor's sensitivity +10mV/V with offset -12mV/V. supply volt8
+5V. full scale (-FS) output sensor then +5V(-12mV/V) -60mV; then (-12mV/V 10mV/V) -10mV. Following through flowchart, gain setting (gain 93V/V) correction setting (+25mV RTI) (Referred-to Input). coarsely corrected input (-60mV 25mV)93 -3.255V. input (-10mV 25mV)93 +1.395V. input range ±VDD. Thus maximum minimum digitized sensor signals become -3.255 -0.651 +1.395 +0.279. Notice that bridge multiplies signal divides signal VDD. Thus, system ratiometric dependent value VDD. output clips ±1.0 when input values exceed ±VDD. best signal-to-noise ratio (SNR) achieved when input within ±85% (Figure MAX1460 includes internal temperature-sensing bridge allowing MAX1460 temperature used proxy sensor temperature. this reason, MAX1460 must mounted thermal proximity sensor. output temperature-sensing bridge also corrected 3-bit coarse-offset processed ADC. selection Temperature Sensor Offset (TSO) bits configuration register should made that digitized temperature signal close possible midscale temperature. This done maximize dynamic range thermal-calibration coefficients (Table
Low-Power, 16-Bit Smart MAX1460
CYCLES
TEST RESET
SDIO
COMMAND COMMAND COMMAND COMMAND
REGISTER DATA FIELD
REG. COMMAND
EEPROM ADDRESS FIELD
NOTE: TRANSITIONS MUST OCCUR WITHIN 100ns CLOCK EDGE.
Figure Test-System Command Timing Diagram
Table Temperature Sensor Offset (TSO) Settings
TSO-2 SETTING TSO-1 TSO-0 TEMPERATURE BRIDGE OFFSET Maximum Minimum
tion RESET begins 32-bit serial transfer testsystem command word through SDIO. test system transitions SDIO falling edges clock; MAX1460 latches data rising edge (Figure 32-bit command word generated test-system divided into four fields (Figure 4-bit command field interpreted Table other fields usually ignored, except that command uses register fields, command requires EEPROM address. command word fields are: Register Data Field: Holds calibration coefficients written into MAX1460 16-bit registers EEPROM Address Field: Holds hexadecimal address EEPROM (from hex) Register Address Field: Contains address register where calibration coefficient written Command Field: Instructs MAX1460 take particular action (Table
Test-System Interface: Writing Calibration Coefficients Registers EEPROM
make MAX1460 respond commands from test system, raise TEST drive with 2MHz clock signal. necessary remove resonator. RESET must least clock cycles initialize MAX1460. Then, rising transi-
Low-Power, 16-Bit Smart MAX1460
Table Test System Commands
COMMAND Write calibration coefficient into register. Block-Erase entire EEPROM (writes bits). Write single EEPROM bit. NOOP (NO-OPeration) Start Conversion command. registers updated with EEPROM values. SDIO enabled outputs. Start Conversion command. registers updated with EEPROM values. SDIO enabled outputs. Start Conversion command. registers updated with EEPROM values. SDIO disabled. Start Conversion command. registers updated with EEPROM values. SDIO disabled. Reserved CODE
Table Calibration Coefficient Registers
COEFFICIENT Gain DOFF REGISTER ADDRESS FUNCTION Gain correction Linear gain Quadratic gain Offset correction Linear offset Quadratic offset Output midscale pedestal RANGE -32768 +32767 -1.0 +0.99997 -1.0 +0.99997 -1.0 +0.99997 -1.0 +0.99997 -1.0 +0.99997 -32768 +32767 FORMAT Integer Fraction Fraction Fraction Fraction Fraction Integer
Writing Registers Command writes calibration coefficients from test system directly into registers. Tester commands cause MAX1460 start conversion using calibration coefficients registers. This direct registers speeds calibration compensation because does require EEPROM write-access time. Bringing RESET clears registers, test system should always write registers start conversion single command timing sequence. shown Table seven registers hold calibration coefficients characteristic equation [DOUT Gain (1+G1T G2T2) (Signal Of1T Of2T2) DOFF] implemented MAX1460 DSP. registers 16-bit, two's complement coding format. When register interpreted integer, decimal range from -32768 (8000 hex) +32767 (7FFF
hex). Fractional coefficient values range from -1.0 (8000 hex) +0.99997 (7FFF hex). register address called Configuration Register. holds coarse offset, gain, Power-Down, temperature-sensor offset, repeat mode, reserved bits, shown Table functionality coarse offset, gain, temperature-sensor bits described Analog Front section. Power-Down enables uncommitted when set. repeat-mode tested last instruction microcode, and, set, immediately initiates another conversion cycle. Maxim reserved bits should altered.
Low-Power, 16-Bit Smart
Table Configuration Register Bitmap
EEPROM ADDRESS (HEX) POSITION (LSB) (MSB) DESCRIPTION CO-0 (LSB) CO-1 (MSB) CO-S (Sign) PGA-1 (MSB) PGA-0 (LSB) Maxim Reserved Maxim Reserved Power-Down Maxim Reserved TSO-0 (LSB) TSO-1 TSO-2 (MSB) Maxim Reserved Maxim Reserved Maxim Reserved Repeat Mode
sarily long because internal charge pump must create maintain voltages above long enough cause reliably permanent change memory. Writing EEPROM requires 6ms, writing EEPROM typically requires less than 400ms. decrease EEPROM write times. write EEPROM bit, test system must compliant with Command Timing Diagram shown Figure performing following operations: Issue command hex, including EEPROM address field written. Issue command hex, with address field used step Continuously repeat this command times (6ms). Issue command hex, including EEPROM address field used steps procedure using command (Block-Erase EEPROM) similar. Record Maxim Reserved bits configuration register prior using this command, restore them afterwards. number Block-Erase operations should exceed 100. Issue command hex. Issue command hex. Continuously repeat this command times (6ms). Issue command hex.
MAX1460
Writing Internal EEPROM test system writes EEPROM with commands (Block-Erase entire EEPROM), (Write single EEPROM bit) (NOOP). During normal operation (when TEST low) when test system issues instructions (Start conversion from EEPROM values), reads Calibration Coefficients from EEPROM. normal production flow, determine calibration coefficients using direct register access. Then load calibration coefficients into EEPROM with tester instruction hex. Instruction block-erases EEPROM necessary only rework reclaim operation. each part, Maxim reserved bits Configuration Register should read before instruction issued, restored afterwards. MAX1460 shipped with internal EEPROM uninitialized, except reserved bits. internal 128-bit EEPROM arranged eight 16bit words. These eight words configuration register seven calibration-coefficient values (Table MAX1460 EEPROM addressable. final calibration coefficients must mapped into EEPROM locations that set. There bitclear instruction. EEPROM write operation neces-
Test System Interface: Observing Operation
Test system commands initiate conversion while allowing test system observe operation DSP. calibrate unit, test system must know digitized temperature sensor signals, stored registers calibrated compensated output stored register test system should also verify EEPROM contents, registers 0-7. these signals pass through register during execution instruction microcode. outputs register values, SDIO tells tester which signal currently
Low-Power, 16-Bit Smart MAX1460
Table EEPROM Memory
Address (hex) Contents Address (hex) Contents Address (hex) Contents Address (hex) Contents Address (hex) Contents Address (hex) Contents Address (hex) Contents Address (hex) Contents Configuration
Gain
DOFF
Table Subset Instruction
INSTRUCTION CODE (PS) (HEX) PROGRAM COUNTER (HEX) REGISTER VALUE Register 0-Configuration Register 1-Gain Register 2-G1 Register 3-G2 Register 4-Of0 Register 5-Of1 Register 6-Of2 Register 7-DOFF Register 8-Temperature Signal Register 9-Sensor Signal Register 10-Compensated Output
There three internal registers that directly observable SDIO pins: 16-bit Scratch Accumulator register, containing result execution current microcode instruction. 8-bit Program Pointer register, which holds address instruction microcode. 8-bit Program Store register. instruction that currently executing. instruction data address instructions relevant test system listed Table After test system sends Start Conversion commands hex, SDIO both enabled MAX1460 serial outputs. test system should disable (high impedance) SDIO driver avoid conflict this time that MAX1460 drive pin. After executes each microcode instructions, contents registers output serial format (Figure instruction state registers delivered every clock cycles, where after Start Conversion command completes. tester should latch SDIO
Low-Power, 16-Bit Smart MAX1460
9)th CLOCK CYCLE
9)th CLOCK CYCLE
SDIO
CYCLE CYCLE CYCLE
NOTE: TRANSITIONS MUST OCCUR WITHIN 100ns CLOCK EDGE.
Figure Serial Output Timing Diagram
tCONV tWARM START (OPTIONAL)
tADC
SDIO (TEST MODE)
tDSP
[11.0]
tEOC
Figure MAX1460 Conversion Timing
bits falling edge clock signal. When registers Table appear SDIO, tester should save corresponding data. conversion timing MAX1460 shown Figure Table figure, conversion initiated rising transition START pin. Equivalently, conversion initiated TEST mode after completion tester commands hex, reinitiated state Repeat Mode configuration register. After conversion initiated, 16-bit digitizes temperature sensor signals during Then, executes
instruction microcode during tDSP. TEST mode, during tDSP, SDIO outputs carry useful information. 130,586 clock cycles after Start Conversion command received, registers available SDIO. last instruction hex. tester start communication sequence lowering RESET least clock cycles, then resume driving SDIO. SDIO becomes high impedance when RESET low.
Low-Power, 16-Bit Smart MAX1460
Table MAX1460 Conversion Timing
PARAMETER Sensor Warm-Up Time Time Time Pulse Width Conversion Time SYMBOL tWARM tADC tDSP tEOC tCONV 130,585 3,220 133,805 UNITS cycles cycles cycles cycles
130,585 3,364 133,949
Applications Information
Calibration Compensation Procedure
Perform fine calibration characterizing sensor/ MAX1460 pair using test system then finding calibration coefficients Gain, Of0, Of1, using equations below. This simple fine-calibration procedure requires three temperatures, denoted sensor excitations, named small large. Thus, there data points (AS, CL); unknown calibration coefficients; versions characteristic equation, form:
Equation
versions equation ratioed obtain:
Equation (2a)
SignalAL Similarly,
Equation (2b)
SignalAS
Of1TA
SignalBL
Equation (2c)
SignalBS SignalCS
SignalCL where
Equation
Of1TB
DOFF Gain G1TC Signal where DOFF determined product specification. desired MAX1460 output corresponding sensor excitation; desired MAX1460 output corresponding sensor excitation; DOFF desired midscale output; SignalCL digitized sensor reading temperature with sensor excitation applied; digitized temperature reading temperature Unstable digitized temperature readings indicate that thermal equilibrium been achieved, necessitating increased soak times better thermal control. Averaging many readings from MAX1460 will help filter variations sensor excitation oven temperature. Begin calibration soaking sensor MAX1460 pair first temperature, apply excitation sensor. Start conversion record digitized temperature digitized signal SignalAL. Apply sensor excitation, record digitized signal SignalAS. Repeat this procedure temperatures recording SignalBL, SignalBS, SignalCL, SignalCS.
Of1TC
DOFF DOFF
Equations form system three linear equations, with three unknowns, Of2. Solve Of0, Of1, Of2. small sensor excitation versions Equation ratioed obtain:
Equation (4a)
(YCS
Equation (4b)
(YCS
Low-Power, 16-Bit Smart MAX1460
UNCOMPENSATED SENSOR ERROR
ERROR (%FSO) TEMPERATURE (°C) OFFSET UNFILTERED BITSTREAM AGND AMP+ 500k AMPMAX1460 AMPOUT FILTERED ANALOG OUTPUT 500k
Figure Sensor Characteristics Before Compensation COMPENSATED TRANSDUCER ERROR
0.20 0.15 ERROR SPAN, 4000 CODES) 0.10 0.05 -0.05 -0.10 -0.15 -0.20 TEMPERATURE (°C) OFFSET
Figure Filtering Output Equation (5c)
DOFF SignalCS Of1TC
Equations form system linear equations unknowns, Solve Equation readily solved last unknown, Gain. Arithmetic manipulation magnify measurement errors noise. Quantization calibration coefficients another reason consider adjusting Gain DOFF coefficients. this, load MAX1460 registers with calculated coefficients Gain, Of0, Of1, Of2, DOFF. Assuming oven still temperature sensor excitation still applied, measure output DCS. Change sensor excitation, measure DCL. Compute Gain coefficient using equation Remeasure DCL, compute DOFF coefficient, given equation
Equation
Figure Compensated Sensor/MAX1460 Pair
where:
Equation (5a)
Equation (5b)
DOFF SignalAS Of1TA
GAINnew Gain
Equation
DOFF SignalBS Of1TB
DOFFnew DOFF final calibration coefficients written into MAX1460 EEPROM. unit ready final test.
Low-Power, 16-Bit Smart MAX1460
This algorithm minimizes error directly test conditions, Space temperatures widely minimize signalto-noise ratio measurement. there large error remaining finished product, move calibration temperatures closer peak error temperatures. Similarly, full-scale sensor excitation best calibration condition sensor nonlinearities. Move away from full scale. Figure shows characteristics individual Lucas-NovaSensor model NPH8-100-EH, 15psig, silicon pressure sensor. Figure shows result compensated sensor/MAX1460 pair.
MAX1460 Evaluation/ Development
MAX1460 evaluation kit) speeds development MAX1460-based transducer prototypes test systems. First-time users MAX1460 strongly encouraged this kit, which includes: Evaluation board, with MAX1460 sample silicon pressure sensor, ready customer evaluation. Interface board that must connected parallel port. MAX1460 communication/compensation software (Windows compatible), which enables programming MAX1460 module time. Detailed Design/Applications manual, developed sensor-test engineers. evaluation order number MAX1460EVKIT.
Using Compensated Sensor/MAX1460 Pair
After calibration removal from test system, MAX1460 sensor form mated pair. START connected left unconnected sensor does require significant warm-up time. operation simple: just apply power latch parallel output when falls. Temperature digitized during first half tADC, MAX1460 provides minimum sensor warm-up time 35ms. Using 2MHz resonator, conversion time tCONV nominally 67ms. Repeat Mode set, conversions repeat rate 15Hz. sensor requires more than 35ms warm-up time, START used initiate conversion (Figure Repeat Mode set, START should remain high. Repeat Mode reset, START used externally control conversion rate MAX1460. After 12-bit parallel output latched, conversion taking START least clock cycle. output converts parallel digital output into serial bitstream OUT. simple external lowpass filter, using MAX1460 amp, converts bitstream into ratiometric analog voltage (Figure filter shown inverting configuration, Gain DOFF coefficients characteristic equation adjusted obtain either polarity. used, powered down using Power-Down configuration register. MAX1460 requires minimum external components: power-supply bypass capacitor (C1) from VSS. 2MHz ceramic resonator (X1). resistors AGND pin. analog output desired, 500k resistors capacitor needed filtering.
Configuration
N.C. XOUT
TEST
N.C. N.C.
N.C. N.C.
N.C. N.C. AGND START I.C. N.C.
N.C. AMPAMP+ AMPOUT N.C. N.C.
MAX1460
RESET
N.C. N.C. SDIO
N.C.
Low-Power, 16-Bit Smart
Functional Diagram
AGND 2MHz RESONATOR XOUT 0.1µF CONFIGURATION REGISTER TEMPERATURE SENSOR CORRECTION COEFFICIENTS REGISTERS 16-BIT DIGITAL SIGNAL PROCESSOR (DSP) 12-BIT DIGITAL OUTPUT 16-BIT TEMPERATURE SENSOR SIGNAL REGISTERS OSCILLATOR CONTROL LOGIC EEPROM INSTRUCTION START TEST RESET SDIO AMP- AMP+
MAX1460
MAX1460
16-BIT INTERFACE SIGNALS AMPOUT
[11.0]
COARSE OFFSET CORRECTION
SENSOR
Chip Information
TRANSISTOR COUNT: 59,855 SUBSTRATE CONNECTED
Low-Power, 16-Bit Smart MAX1460
NOTES
Low-Power, 16-Bit Smart MAX1460
NOTES
Low-Power, 16-Bit Smart MAX1460
NOTES
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 1999 Maxim Integrated Products Printed registered trademark Maxim Integrated Products.

Low-Power, 16-Bit Smart Low-Noise, 400µA Single-Chip Sensor Signa

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