PGA309 Programmable Sensor Signal Conditioner. Bringing Linearity to a Non-Linear Pressure Sensor World

Transcription

1 PGA309 Programmable Sensor Signal Conditioner Bringing Linearity to a Non-Linear Pressure Sensor World

2 Typical Wheatstone Bridge Pressure Sensor Bridge Resistance is Symmetrical

3 Pressure Sensor Terminology Span (Scale factor for V INP -V Full-Scale Pressure relative to V EXC ) FSO (Full Scale Output) FSS (Full Scale Sensitivity) Gain Sensitivity i.e. 2mV/V (implies V INP -V INN = FS Pressure with V EXC =+5V) Offset (V INP -V Zero Pressure ) Zero i.e. 10mV

4 Definition of Offset & Span

5 Ideal Span Ideal Span & Offset Ideal Offset

6 Real World Sensors Span 25 o C Linear changes with Temperature NonLinear changes with Temperature Offset 25 o C Linear changes with Temperature NonLinear changes with Temperature Bandwidth <4kHz for most pressure sensor applications

7 Typical Pressure Sensor NonLinearities Initial Offset: -2%< Offset <+2% (of V EXC ) OffsetTC1: -0.1%< OffsetTC1 <+0.3% (of Span/ o C) (Linear Offset Temperature Coefficient) OffsetTC2: -0.5%< OffsetTC2 <+0.5% (of Span) (NonLinear, Second-Order, Offset Temperature Coefficient) Initial Span: -0.4%< Span <+16% (of V EXC ) SpanTC1: -0.3%< SpanTC1 <+0.3% (of Span/ o C) (Linear Span Temperature Coefficient) SpanTC2: -2%< SpanTC2 <+3% (of Span) (NonLinear, Second-Order, Span Temperature Coefficient) Many Sensors also have higher order NonLinearities

8 Typical OffsetTC Offset TC Vs. Temperature Offset TC (%Span) ( OffsetTC1T ( )) OffsetTC1= 0.2%Span/ C T Temperature (C) 125

9 Typical OffsetTC2 Offset NonLinearity (%Span) Offset NonLinearity Vs. Temperature OffsetTC2( T) OffsetTC2= 3%Span 1.25 (OffsetTC2= 4.41x10-4 %Span/ C 2 ) T Temperature (C) 125

10 Offset (%Span) OffsetT ( T) Typical Total Offset vs Temp Offset Vs. Temperature T Temperature (C) 25 C= 2%V EXC OffsetTC1= 0.2%Span/ C OffsetTC2= 3%Span 125

11 Typical SpanTC1 Span TC (%Span) 13 SpanTC1T ( ) 20 Span TC Vs. Temperature SpanTC1= -0.2%Span/ C T Temperature (C) 125

12 Typical SpanTC2 Span NonLinearity (%Span) 0 Span NonLinearity Vs. Temperature SpanTC2( T) SpanTC2= -2%Span 1.65 (SpanTC2= -2.94x10-4 %Span/ C 2 ) T Temperature (C) 125

13 Span (%Span) Typical Total Span vs Temperature Span Vs. Temperature SpanTT ( ) C= 2%V EXC 20 SpanTC1= 0.2%Span/ C 22.5 SpanTC2= 3%Span T Temperature (C) 125

14 Pressure NonLinearity Many Bridge Sensors also have NonLinear Outputs with applied Pressure Typical Pnl (Pressure NonLinearity) -2.5%< Pnl <+2.5% (of Span)

15 Pnl (Pressure NonLinearity) Example Pressure (PSI) Pin 100 PnonlinPin ( ) NonLinear Pressure Output of Sensor Pin Pmax Normalized Pressure Stimulus Pnl = 2.5%Span 1

16 Pnl (Pressure NonLinearity) Example Pressure Nonlinearity (%Span) 2.5 Pressure NonLinearity Vs. Stimulus P NL ( Pin) Pnl = 2.5%Span Pin 1 Pmax Normalized Stimulus

17 Traditional Trim for NonLinearities V BR+ Sensitivity Drift Trim Offset Drift Trim V INP I excitation Zero Trim1 Zero Trim2 V INM V BR-

18 Traditional Trim for NonLinearities Requires special pre-package fixtures Requires special laser or manual resistor trims Trims are interactive with each other Multiple test/trim/test/trim passes required Finite number of trims and range No 1-step easy trim for electronics & sensor

19 Modern Digital Trim for NonLinearities V S PGA309 Non-Linear Bridge Transducer V EXC Analog Sensor Linearization Linearization Ckt Ref Linearization DAC Fault Monitor Auto-Zero PGIA Over/Under Scale Limiter Linear V OUT + Analog Signal Conditioning Ext Temp Digital Temperature Compensation Ext Temp Int Temp Temp ADC Control Register Interface Circuitry DIGITAL CAL EEPROM (SOT23-5)

20 Modern Digital Trim for NonLinearities Allows for final post-package trim Simple digital trim with computer calculated calibration coefficients. Almost infinite number of trims with finer resolution and wider range Less interaction between trims 1-step easy trim for electronics & sensor

21 Typical 3-Terminal Sensor Module Application Pressure Connection Sensor Module Housing PGA309 EEPROM Electrical Connection V S V OUT GND Bridge Pressure Sensor Electronics

22 PGA309 Overview

23 PGA309 Inside Tour Gain Blocks Front End PGA Output Amplifier & Fine Gain Adjust Combined Gain Settings Offset Coarse Offset Adjust Fine Offset Adjust Reference: Internal/External Monitor Functions Fault Monitor: Internal/External Comparators Scale Limits: Over-Scale/Under-Scale Temperature Sense Internal/External Excitation Linearization Dynamic Digital Temperature Compensation Digital Interface Options for Calibration Two-Wire Single-Wire

24 PGA309 Inside Tour Will Use Definition by Example: Bridge Sensor: 0psi < Pin < 100psi FSO = 2mV/V Pnl = +2.5% FSR Calibrated PGA309 + Sensor Pin = 0psi, VOUT = 0.5V Pin = 100psi, VOUT = 4.5V

25 PGA309 Gain Blocks

26 PGA309 Front End PGA

27 PGA309 Output Amplifier & Fine Gain Adjust

28 PGA309 Offset Coarse Offset Positive or Negative Applied before Front End PGA Gain Fine Offset 16-Bit, Range: 2%V REF to 98%V REF (For V REF =5V) For RTO: Amplified by Fine Gain Adjust & Output Amplifier Gain

29 PGA309 Reference Internal Reference +2.5V V 2.4%Initial Accuracy +10ppm/ C Drift External Reference +1.25V to V S Power-on to External Ref

30 Fault Monitor External Comparators Case INN_HI (ALM3) INN_LO (ALM2) INP_HI (ALM1) INP_LO (ALM0) Normal RB1 open RB2 open RB3 open RB4 open RB1 short RB2 short RB3 short RB4 short open sensor gnd open sensor V EXC V EXC short gnd 1* 1 1* 1 V IN1 (V INP ) open V IN2 (V INN ) open V IN1 (V INP ) short gnd V IN2 (V INN ) short gnd V IN1 (V INP ) short V EXC V IN2 (V INN ) short V EXC V IN1 (V INP ), V IN2 (V INN ) open V IN1 (V INP ), V IN2 (V INN ) short gnd V IN1 (V INP ), V IN2 (V INN ) short V EXC * Typically a logic 1 but not guaranteed by design and nature of fault Minimum Select Circuit for Inx_HI Comparators: When V EXC enabled the lower of V EXC -100mV and V SA -1.2V is used as comparator reference. Ensures fault monitor when V EXC increases due to linearization circuit and bridge has faults which violate positive V CM of front end PGA.

31 Fault Monitor Internal Comparators Front End PGA Linear Range Monitor A2 Positive Saturation A2 Negative Saturation A1 Positive Saturation A1 Negative Saturation A3 Common Mode Mostly Used During Calibration V OUT can be valid but Internal Nodes invalid! Faults Indicate Improper Gain Settings Wrong coarse offset polarity/value Incorrect Fine Offset DAC setting

32 Fault Monitor Comparator Flags INP_HI External Comparator Fault Flag EXTPOL 1=Force V OUT High 0=Force V OUT Low Internal Comparator Fault Flag Enable/Disable External Comparators INP_LO INN_HI INN_LO 1=Fault EXTEN 1=enable 0=disable 1=close 0=open 0 1 V S Polarity to Force V OUT External Comparator Fault Flag Enable/Disable Polarity to Force V OUT Alarm Status Register - Output Amplifier + V OUT External Comparator Fault Flag Supersedes Internal Fault Flag when fault detected A2SAT_LO A2SAT_HI 1=Fault 1=close 0=open Internal Comparators A3_VCM A1SAT_LO A1SAT_HI Internal Comparator Fault Flag INTEN 1=enable 0=disable INTPOL 1=Force V OUT High 0=Force V OUT Low 0 1 V S

33 Over/Under Scale Limit

34 A/D Range Budget

35 Internal Temperature Sensor Similar to TMP100 +/-2 C initial Accuracy +/ C typical resolution 12 Bit + Sign data -128 C to +128 C Range Temperature errors calibrated out when PGA309 + Sensor calibration is performed

36 External Temperature Sense Temp ADC Resolution: 11Bit+Sign to 15Bit+sign

37 External Temp Sense - Configuration

38 PGA309 Linearization Loop Diagram

39 Linearization Circuit Details V LIN_DAC (-0.166<V LIN_DAC <+0.166) 7 Bit+Sign X0.166 DAC X0.83 Range 0 V REF REF IN / REF OUT 4.096V 2.5V Internal Select V EXC OR - Output Amplifier + V OUT (-0.124<V LIN_DAC <+0.124) X Bit+Sign DAC X0.52 Range 1 V REF REF IN / REF OUT 4.096V Internal Select 2.5V

40 PGA309 V EXC Linearization Example of Non-Linear Bridge Output vs Pressure Input P MIN = 0psi, P MAX = 100psi, %NL = +2.5% NonLinear Pressure Output NonLinear Bridge Pressure Output (psi) Linear System Pressure Input Pressure (psi) Normalized Stimulus (P/P MAX )

41 PGA309 V EXC Linearization Example Bridge Output Non-Linearity vs Pressure Input PMIN = 0psi, PMAX = 100psi, %NL = +2.5% Nonlinearity vs Stimulus Nonlinearity (%FSR) Normalized Stimulus (P/P MAX )

42 PGA309 Final Sensor V EXC Linearization 0.06 VOUT Error vs VOUT Error (%FSR) Pressure (psi)

43 Summary of PGA309 + Sensor Calibration Bridge Output V INP - V INN Bridge Output V INP - V INN

44 Dynamic Digital Temperature Compensation Zero DAC Adjustment Gain DAC Adjustment PGA309 Configuration Registers External EEPROM (SOT23-5) Temperature Index Zero DAC Gain DAC T0 Z0 G0 Temperature ADC Temperature Code Linear Interpolation Logic Temperature Index Zero DAC Gain DAC T16 Z16 G16 Temperature Compensation Cycle: Every 150mS Temperature ADC converts (Temperature Code) Temperature Index values are read Linear Interpolation algorithm between closest Temperature Index values occurs Final Zero DAC and Gain DAC Adjustment Values computed

45 Digital Interface Options for Calibration

46 PGA309DK (Designer s Kit) Allows User: Complete Evaluation of PGA309 + Sensor Ease of Temperature Coefficient Calculations Immediate Program/Test Bench to Ship First Production Units

47 PGA309DK Hardware Designer s Kit (PGA309DK) Evaluate PGA309 and Sensor Full Temperature Evaluation Software Control For Designer s Kit Program PGA309 for Evaluation Program PGA309 for First Production Run Sensor Computation Analysis Tool

48 Easy 4-20mA PGA309 Application

49 PGA309 + XTR115 Programming w/pga309dk

50 PGA309 Key Features Gain Range: X2.7 (700kHz BW) to X1152 (60KHz BW) Fine Gain Adjust: 16-Bit DAC, 0.33 to 1 Range Fine Offset Adjust: 16-Bit DAC, 0.1V to 4.9V Range (V REF =5V) Coarse Offset Adjust: +/-60mV (V REF =5V) Bandwidth: 700kHz (X2.7), 60kHz (X1152) Reference Voltage: Internal (2.5V/4.096V) or External Internal or External Temperature Sense Temperature Calibration Span & Offset Look-up Table Logic w/linear Interpolation Up to 17 Temperature Coefficients Digital Calibration: Single-Wire or Two-Wire Interface Voltage Output: Ratiometric or Absolute Small TSSOP-16 Package -40 C to +125 C Operation +2.7V to +5.5V Operation Fault Monitor/Detection Over/Under-Scale Limits Excitation Linearization

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