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Texas Instruments PGA309, Quick Start Manual

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Texas Instruments PGA309 Quick Start Manual Download Page 60

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

60

PGA309 Ratiometric 
Calibration Example

This example walks through the PGA309 ratiometric calibration technique.   
The PGA309 Absolute Calibration example is a more detailed description of a 
calibration, and so, it is recommended that you review this example first. This 
document describes the key elements that are required in a ratiometric 
calibration, but does not fully explain how to use the PGA309 Gain Calculator, 
Sensor-Emulator-EVM, or the Designers Kit Control Program.

For information on these development tools, please see the PGA309 Product 
Folder on the TI website, at 

www.ti.com

. 

Summary of Contents for PGA309

Page 1: ...PGA309 Quick Start System Reference Guide by Art Kay High Precision Linear Products SBOA103C Jan 2006 ...

Page 2: ...SBOA103C Jan 2006 PGA309 Quick Start System Reference Guide 2 PGA309 Quick Start ...

Page 3: ...ork for your application 14 17 Step 2 Set up hardware 18 21 Step 3 Configure PGA309 for initial scaling 22 31 Step 4 Configure Sensor Emulator EVM to emulate sensor 32 38 Step 5 Use the Calibration Spreadsheet to perform the calibration 39 59 PGA309 Ratiometric Calibration Example 60 86 PGA309 With Output Scaling Example 87 95 PGA309 In Three Wire Mode 96 100 PGA309 Quick Start Contents ...

Page 4: ...ntiometer Software PGA309DK Board Interface This software is used to communicate with the PGA309EVM See http focus ti com docs toolsw folders print pga309evm eu html under support software for free download PGA309 Calculator This software is used to do initial gain scaling and verify that the design does not violate any PGA309 specifications Software is bundled with PGA309DK Board Interface softwa...

Page 5: ...n at room temperature OffsetTC2 The second order quadratic drift of the offset This coefficient is in of span oC2 at room temperature Span the amount of change in normalized output voltage in V V of the sensor over the entire range of applied stimulus SpanTC1 The linear drift of the sensors span given in of span oC NonlinSpanDrift The second order quadratic drift of the offset This coefficient is ...

Page 6: ...Quick Start System Reference Guide 6 Span the amount of change in normalized output voltage in V V of the sensor over the entire range of applied stimulus Offset the normalized output of a sensor in V V with no applied stimulus ...

Page 7: ...dge Sensitivity vs Temp 5 0E 04 0 0E 00 5 0E 04 1 0E 03 1 5E 03 2 0E 03 2 5E 03 3 0E 03 3 5E 03 4 0E 03 50 0 50 100 150 Temp degC Kbridge V V offset span T2 Span2 22 5C 3 67E 3 T3 Offset3 85C 2 96E 6 T2 Offset2 22 5C 1 02E 3 T1 Offset1 40C 1 62E 3 Linear end point fit is used to determine the linear drift The linear drift of the sensor s offset given in of span oC OffsetTC1 ...

Page 8: ...5 40 2 2 1 269 10 5 of span oC2 Bridge Sensitivity vs Temp 5 0E 04 0 0E 00 5 0E 04 1 0E 03 1 5E 03 2 0E 03 2 5E 03 3 0E 03 3 5E 03 4 0E 03 50 0 50 100 150 Temp degC Kbridge V V offset span OffsetTC2 The second order quadratic drift of the offset This coefficient is in of span oC2 at room temperature NonlinOffsetDrift The second order quadratic drift of the offset This coefficient is in of span at ...

Page 9: ...E 04 0 0E 00 5 0E 04 1 0E 03 1 5E 03 2 0E 03 2 5E 03 3 0E 03 3 5E 03 4 0E 03 50 0 50 100 150 Temp degC Kbridge V V offset span SpanTC1 Span3 Span1 Span2 T3 T1 SpanTC1 3 728410 3 3 441210 3 3 6734 10 3 85 40 6 255 10 4 of span oC The linear drift of the sensors span given in of span oC SpanTC1 ...

Page 10: ...3 1 5E 03 2 0E 03 2 5E 03 3 0E 03 3 5E 03 4 0E 03 50 0 50 100 150 Temp degC Kbridge V V offset span T3 Span3 85C 3 73E 3 T1 Span1 40C 3 44E 3 T2 Span2 22 5C 3 67E 3 The nonlinear coefficient assumes T2 is equal distant t o T1 and T3 Thus the vertex of the parabola will be at T2 NonlinSpanDrift The second order quadratic drift of the offset This coefficient is in of span at room temperature NonlinS...

Page 11: ... real_sensor 100 real_sensor 0 stim100 stim0 3 67 10 3 0 100 0 3 67 10 5 ideal_sensor stim slope stim ideal_sensor 50 3 67 10 5 50 1 835 10 3 PresureNonlinearity real_sensor 50 ideal_sensor 50 real_sensor 100 100 1 66 10 3 1 835 10 3 3 67 10 3 100 4 768 The second order quadratic nonlinearity versus applied signal given in of span Note These readings were all taken at room temperature So real_sens...

Page 12: ...T Troom OffsetTC2 T Troom 2 SensorOutput P T Offsetroom Spanroom Offset_TC T Span Nonlinearity_pct 100 1 Span_TC T The equations use the constants defined on the previous slides These equations are used in the generate_emu_settings xls spreadsheet to compute the voltage settings for the Sensor Emulator EVM Sensor Output Equations Available for download at www ti com as SBOC065 ...

Page 13: ...this quick start example the specifications below and the example hardware configuration will be used The Sensor Emulator EVM will create an equivalent for the illustrated Real World Inputs generate_sim_values xls Offset and Span Tab PGA309 Absolute Calibration Example ...

Page 14: ... s specifications with the PGA309 Calculator software tool SLVC073 to see if the PGA309 has the gain and offset adjustment range required to accommodate your sensor Use the PGA309 Calculator software tool to verify that your design does not violate any of the most critical PGA309 specifications internal or external nodes ...

Page 15: ... values shown Press Compute Constants and the resulting gain settings will be displayed here Enter your sensor parameters and your PGA309 configuration parameters to get the gain scaling If your design generates values for gain and offset that are out of the PGA309 s range the software will flag the problem ...

Page 16: ...ble range The Set Additional Constraints button is a way to force the front end gain or coarse offset to a constant For this example set the coarse offset zero to minimize noise Click Apply Constraints and then click Compute Constants In this case the range of adjustment for the Zero DAC is reduced but is still adequate to correct for the sensor drift ...

Page 17: ...SBOA103C Jan 2006 PGA309 Quick Start System Reference Guide 17 After the gains and offsets of the PGA309 have been calculated press Simulate Device to see if any internal nodes are out of range ...

Page 18: ...Using the Sensor Emulator This diagram illustrates an example of how the Sensor Emulator EVM would be used in an engineering bench setup The PGA309 is a programmable sensor signal conditioning chip The Sensor Emulator EVM can be used in conjunction with the PGA309EVM both versions to facilitate the development of the PGA309 application ...

Page 19: ...SBOA103C Jan 2006 PGA309 Quick Start System Reference Guide 19 Jumper setup of PGA309EVM xx and connections to PC power and the Sensor Emulator EVM ...

Page 20: ...SBOA103C Jan 2006 PGA309 Quick Start System Reference Guide 20 Required Electrical Connections to Sensor Emulator EVM ...

Page 21: ...e emulated diode voltages Sensor Emulator EVM Jumper Setup These three channels are used to set the temperature output signal in the diode mode The Rt channels are not used in this mode Set the jumper JUMP1 to the position shown to connect the Diode temperature emulation Set the jumper JUMP5 to the position shown to connect GND to the bottom of the bridge emulator ...

Page 22: ...tep 3 Do initial setup of the PGA309 using the PGA309 DK Program Copy the PGA309 Calculator results into the PGA309DK software Configure the PGA309 Temp ADC Calibrate the ADS1100 ADC on PGA309EVM xx PC Interface Board Used to read the PGA309 output read via software ...

Page 23: ...09 Designer s Kit Control Program When it starts a message box will ask if you want to load from the EEPROM Press No Another box will indicate that the PGA309 EVM was detected using the One Wire interface If the PGA309EVM does not work properly refer to the PGA309EVM Users Guide ...

Page 24: ...ill measure the PGA309 output voltage using an delta sigma A D converter on the PGA309 PC Interface Board the ADS1100 For optimal accuracy the ADS1100 should be calibrated To calibrate the ADS1100 measure the supply voltage Vs on the PGA309 PC Interface Board this should be close to 5V ...

Page 25: ...SBOA103C Jan 2006 PGA309 Quick Start System Reference Guide 25 Press the Board Settings button to enter the calibration factors Enter the measured value for Vs then click Read ADS1100 ...

Page 26: ... PGA309 Quick Start System Reference Guide 26 For the next part of the ADS1100 calibration the input of the ADS1100 is shorted The two boards must be separated so that the PGA309 output is not shorted by the calibration ...

Page 27: ...s calibrate ADS1100 This will short the input to the ADS1100 and measure the offset The calibration will take a few seconds When it is complete close the window When this step is done plug the two PGA309EVM boards back together At this point the calibration is complete ...

Page 28: ...is checked During calibration the PGA309 test pin must be set high This pin prevents the PGA309 from reading the EEPROM during calibration Step A It is a good practice to press reset at the beginning of a calibration to insure all the registers are in a known state Initial Configuration for the PGA309 ...

Page 29: ...SBOA103C Jan 2006 PGA309 Quick Start System Reference Guide 29 Set the reference and bridge excitation voltage to the proper values used in the PGA309 Calculator ...

Page 30: ...SBOA103C Jan 2006 PGA309 Quick Start System Reference Guide 30 Copy the gain and offset settings from the PGA309 Calculator to the PGA309 Designer s Kit Control Program ...

Page 31: ...C by pressing the ADC Config button The example settings shown are good for a diode measurement Step B Enter the example settings shown for a diode temperature measurement Press OK when done Step C Press Write PGA309 to copy all the information entered in the program into the registers of the PGA309 ...

Page 32: ... simple you adjust the Sensor Emulator EVM output to mimic your sensor 2 In the case where you want to use a sensor data sheet to configure the Sensor Emulator EVM you can use the generate_emu_settings xls to translate your specifications to Sensor Emulator EVM settings Unfortunately sensor manufacturers may have specifications that do not conform to a standard and sometimes the specifications are...

Page 33: ... part of the PGA309EVM xx 6 PGA309 RatioMetric Error Allows you to read and compute error for a ratiometric PGA309 setup If the raw output of the sensor is not known the Generate_Sim_Values xls spreadsheet can be used to translate the specifications of your bridge sensor and temperature sensor to system voltage levels The spreadsheet contains five sections Offset and Span Diode Vo Rt Rt PGA309 Err...

Page 34: ...output voltage settings for each channel on the sensor emulator The next several pages will show how the voltages listed in the spreadsheet are used to program the Sensor Emulator EVM Enter these for our example Set Sensor Emulator EVM potentiometers to generate these voltages as detailed in pages 35 36 Generates the bridge output voltages from sensor specifications Generate_Sim_Values xls Offset ...

Page 35: ...sents a applied stimulus and temperature combination for the sensor Adjust the potentiometers coarse first then fine to match the values computed by the Generate_Sim_Values xls spreadsheet for cold 0 50 100 room 0 25 50 75 100 and hot 0 50 100 For example the sensor output at cold temperature and 0 of applied stimulus is emulated by this channel The rotary switch S1 is used to select this channel ...

Page 36: ...fset span This is another example illustrating how a particular channel on the sensor emulator represents an applied stimulus and temperature combination for the sensor In this example the sensor output at cold temperature and 100 of applied stimulus is emulated by this channel The rotary switch S1 is used to select this channel When the channel is selected LED D103 will light to indicate that the...

Page 37: ...Note that the Temp ADC areas are specific to the PGA309 sensor signal conditioning chip The Temp ADC values will be used in the computation of the Counts for the temp ADC The next several pages will show how the diode voltages are used to program the sensor Sensor Emulator EVM Adjust the Diode section potentiometer on the Sensor Emulator EVM to generate the counts as detailed on page 38 PGA309 Tem...

Page 38: ...rature sensor Using the Temp DVM adjust the respective potentiometers coarse first the fine to match the values computed by the Generate_Sim_Values xls spreadsheet for Diode Cold Diode Room and Diode Hot For this example the temperature output signal at cold temperature 45o C is emulated by this channel The rotary switch S2 is used to select this channel When the channel is selected LED D201 will ...

Page 39: ...ct the calibration algorithm Copy the PGA309 registers into the spreadsheet Use the Sensor Emulator EVM to generate the sensor outputs over temperature Store calibration results into a file Load this into the PGA309 external EEPROM Measure the post calibration error Perform a second calibration to improve accuracy ...

Page 40: ... also generate a coefficient that the PGA309 will use to correct for nonlinearity verses applied pressure Note you will need to enable macros and load the analysis toolpack to get this Excel sheet to work properly Information regarding configuration of Excel is detailed in the PGA309EVM Users Guide When you bring up the spreadsheet it will ask you if you want to start the program Press No because ...

Page 41: ...OA103C Jan 2006 PGA309 Quick Start System Reference Guide 41 Press Load registers from PGA309 to copy the registers from the evaluation fixture into the spreadsheet PGA309 Calibration Spreadsheet Main Tab ...

Page 42: ...ference Guide 42 Press Prepare Calibration Sheet to select the algorithm In this example we will do a 3 temperature 3 pressure calibration Press OK after you have selected 3 Temperature 3 Pressure calibration PGA309 Calibration Spreadsheet Main Tab ...

Page 43: ...GA309 Quick Start System Reference Guide 43 Next the program will ask what type of Temperature Measurement Method you want to use For this example we use the diode method PGA309 Calibration Spreadsheet Sensor Curvefit Tab ...

Page 44: ...SBOA103C Jan 2006 PGA309 Quick Start System Reference Guide 44 When the template for your calibration algorithm is loaded this box will pop up Press OK PGA309 Calibration Spreadsheet Sensor Curvefit Tab ...

Page 45: ...tart System Reference Guide 45 When the Load registers from PGA309 button on the Main sheet was pressed the PGA309 registers were copied into this section of the Sensor Curvefit sheet PGA309 Calibration Spreadsheet Sensor Curvefit Tab ...

Page 46: ...ment temperatures The measurement temperatures are the temperatures that the calibration measurements are made at The appropriate values need to be entered manually for the temperature range This is the range that the curve fit is done over Enter the values shown for our example PGA309 Calibration Spreadsheet Sensor Curvefit Tab ...

Page 47: ...g in active cell button This will insert a PGA309 Temp ADC in counts into that cell The measured PGA309 Temp ADC readings need to be recorded at the respective applied temperatures Use the temperature selector switch on the Sensor Emulator EVM to generate room hot and cold readings for this example PGA309 Calibration Spreadsheet Sensor Curvefit Tab ...

Page 48: ...ill insert a PGA309 output voltage reading from the ADS1100 delta sigma ADC into that cell The PGA309 output voltage needs to be recorded at the appropriate applied pressure and temperature Use the bridge selector switch on the Sensor Emulator EVM to generate the respective room 0 50 100 hot 0 25 50 75 100 and cold 0 50 100 PGA309 Calibration Spreadsheet Sensor Curvefit Tab ...

Page 49: ... the calibration measurements are complete look at the graphs located on the sensor Curvefit sheet These graphs are an easy way to check for gross problems The graphs shown are indicative of typical results for example PGA309 Calibration Spreadsheet Sensor Curvefit Tab ...

Page 50: ... Start System Reference Guide 50 Enter the output voltage scale the number of points in the table and the look up table temperature range For our example enter the values shown PGA309 Calibration Spreadsheet Calibration Results Tab ...

Page 51: ... the mathematical model of the sensor that is developed by the spreadsheet Range2 This is the range that the look up table is developed over This range must be a subset of Range1 It is ok for Range2 and Range3 to be equivalent This range over which the calibrated sensor will correct for temperature drift Note about the temperature ranges PGA309 Calibration Spreadsheet Sensor Curvefit Tab PGA309 Ca...

Page 52: ... offset ranges in the calibration table The Vout max and min calibrated result graph gives an idea of what errors you will see based on the resolution of internal components Note the output should approximately match the values entered in the Enter Output Scale section PGA309 Calibration Spreadsheet Calibration Results Tab ...

Page 53: ...ibration table that will be loaded into the EEPROM is displayed on the Calibration Results tab on the spreadsheet At this point the initial calibration is complete and the table can be uploaded into the PGA309 EEPROM PGA309 Calibration Spreadsheet Calibration Results Tab ...

Page 54: ...6 PGA309 Quick Start System Reference Guide 54 Press the Save Registers Lookup Table button This will store the lookup table into a file that can be loaded into the PGA309 EEPROM PGA309 Calibration Spreadsheet Main Tab ...

Page 55: ... will read the EEPROM and adjust offset and gain for each temperature conversion Step D Press the Read PGA309 to see the updated register values After Step D the initial calibration is complete Step C Press Write EEPROM to store the lookup table in the external EEPROM Step A Press the Open File button to get the file containing the calibration results ...

Page 56: ...1 to 0 3 The PGA309 Error tab on the generate_sim_values xls is a convenient way to do a post calibration error analysis To use it select the blue cell corresponding to the current setup and press the Insert Vout reading in active cell button This will insert the PGA309 output reading from the ADS1100 generate_sim_values xls PGA309 Error Tab ...

Page 57: ...temperature and entered here For this example use the Sensor Emulator EVM to generate 0 and 100 pressure at room temperature Note the correction factors are developed based on these readings These are used to calibrate the Lin_Dac errors not previously accounted for PGA309 Calibration Spreadsheet Sensor Curvefit Tab ...

Page 58: ...ondary calibration measurements store the calibration results into a file and load them into the PGA309 as with the first calibration The file for this example calibration is saved on the PGA309 Quick Start Disk and is called quick_start_second txt Your results should be similar to this file PGA309 Calibration Spreadsheet Main Tab ...

Page 59: ...9 The secondary calibration can be done to significantly reduce the error Post secondary calibration errors are typically on the order of 0 05 The secondary calibration involves making two measurements at room temperature generate_sim_values xls PGA309 Error Tab ...

Page 60: ...re detailed description of a calibration and so it is recommended that you review this example first This document describes the key elements that are required in a ratiometric calibration but does not fully explain how to use the PGA309 Gain Calculator Sensor Emulator EVM or the Designers Kit Control Program For information on these development tools please see the PGA309 Product Folder on the TI...

Page 61: ...ge sensor and the Diode Note that the device power supply is used to provide excitation for the sensor So for this configuration the Vexc pin on the PGA309 is not used and consequently the PGA309 cannot correct for nonlinearity verses applied stimulus Temperature nonlinearities of span and offset will still be corrected Vexc Vin Vin Temp PGA309 Vsa 5V GND Ref_In Ref_Out Real World Inputs PGA309 Ra...

Page 62: ...A103C Jan 2006 PGA309 Quick Start System Reference Guide 62 This diagram illustrates PGA309EVM jumper settings for a ratiometric system Sensor Emulator EVM connections and power connections are also shown ...

Page 63: ...SBOA103C Jan 2006 PGA309 Quick Start System Reference Guide 63 Required Electrical Connections to Sensor Emulator EVM ...

Page 64: ...e emulated diode voltages These three channels are used to set the temperature output signal in the diode mode The Rt channels are not used in this mode Set the jumper JUMP1 to the position shown to connect the Diode temperature emulation Set the jumper JUMP5 to the position shown to connect GND to the bottom of the bridge emulator Sensor Emulator EVM Jumper Setup ...

Page 65: ...Jan 2006 PGA309 Quick Start System Reference Guide 65 The PGA309 Calculator can be used to compute the gain and offset settings for the PGA309 These are the values used for this ratiometric example configuration ...

Page 66: ...Jan 2006 PGA309 Quick Start System Reference Guide 66 In the ratiometric configuration the power supply Vs is being used as the reference Thus it is very important that the supply is measured during calibration ...

Page 67: ...mputed by the calculator need to be written into the PGA309 using the PGA309 Designer s Kit Control Program Step A During calibration the PGA309 Test Pin High must be checked to prevent the PGA309 from reading the EEPROM during calibration Step C The value measured for Vs must be typed in here After all the values are entered press Write PGA309 ...

Page 68: ...nt using the built in 2 048V reference It is important to use the built in ADC reference because the diode measurement is absolute and all the other references are relative to the power supply for this configuration Configure the Temp ADC as shown and click OK From the main window press Write PGA309 Set up the PGA309 Temperature ADC ...

Page 69: ...levels The sensor specifications are entered here The definitions of the different parameters is described earlier in this document Note that Vexc Vs for ratiometric Enter these for our example Note that Pressure Nonlin is zero The sensor must be linear for this configuration because the sensor excitation is the power supply and so the nonlinearity correction circuit cannot be used generate_sim_va...

Page 70: ...ions have been entered the spreadsheet will display the bridge output versus temperature The bridge output versus applied stimulus is also displayed This must be a linear function for a ratiometric setup that does not use Vexc for bridge excitation generate_sim_values xls Offset and Span Tab ...

Page 71: ...st the potentiometers coarse first then fine to match the values computed by the Generate_Sim_Values xls spreadsheet for cold 0 50 100 room 0 25 50 75 100 and hot 0 50 100 For example the sensor output at cold temperature and 0 of applied stimulus is emulated by this channel The rotary switch S1 is used to select this channel When the channel is selected LED D101 will light to indicate that the co...

Page 72: ...et for Diode Cold Diode Room and Diode Hot For this example the temperature output signal at cold temperature 45o C is emulated by this channel The rotary switch S2 is used to select this channel When the channel is selected LED D201 will light to indicate that the correct channel is selected This is the Diode Vo tab on the Generate_Sim_Values xls spreadsheet It is used to compute diode voltages t...

Page 73: ...sure and temperature to create a lookup table that the PGA309 will use to compensate for offset and gain drift The spreadsheet will also generate a coefficient that the PGA309 will use to correct for nonlinearity verses applied pressure Note you will need to enable macros and load the analysis toolpack to get this Excel sheet to work properly Information regarding configuration of Excel is detaile...

Page 74: ...ference Guide 74 Press Prepare Calibration Sheet to select the algorithm In this example we will do a 3 pressure 3 temperature calibration Press OK after you have selected 3 Temperature 3 Pressure calibration PGA309 Calibration Spreadsheet Main Tab ...

Page 75: ...GA309 Quick Start System Reference Guide 75 Next the program will ask what type of Temperature Measurement Method you want to use For this example we use the diode method PGA309 Calibration Spreadsheet Sensor Curvefit Tab ...

Page 76: ...oad Registers From PGA309 button was pressed from the main tab The temperature ranges and pressure ranges need to be entered by hand The TempADC readings and VoutMeas values need to be measured This can be done using the Insert TempADC reading in active cell and Insert Vout reading in active cell buttons PGA309 Calibration Spreadsheet Sensor Curvefit Tab ...

Page 77: ...s for nonlinearity error This value needs to be very small for this configuration because nonlinearity correction is not used This value will not be used to generate the calibration tables in the EEPROM The value of Klin stored in the EEPROM will be zero for this mode because Vexc is disabled PGA309 Calibration Spreadsheet Sensor Curvefit Tab ...

Page 78: ...8 For the ratiometric calibration method the secondary calibration is not necessary The secondary calibration is used to correct for errors introduced by the LinDac So for this example this section is left blank PGA309 Calibration Spreadsheet Sensor Curvefit Tab ...

Page 79: ...ck Start System Reference Guide 79 Select the desired post calibration output range Select the temperature range of the look up table Make sure the Result Sanity Check passes PGA309 Calibration Spreadsheet Calibration Results Tab ...

Page 80: ...GA309 Quick Start System Reference Guide 80 Press Save Registers Lookup Table The spreadsheet will let you know that Excitation is Disabled This is normal for the ratiometric method PGA309 Calibration Spreadsheet Main Tab ...

Page 81: ...e the PGA309 will read the EEPROM and adjust offset and gain for each temperature conversion Step D Press the Read PGA309 to see the updated register values Step C Press Write EEPROM to store the table on the EEPROM Step A Press the Open File button to get the file containing the calibration results After Step D the calibration is complete ...

Page 82: ...post calibration error analysis To use it select the blue cell corresponding to the current setup and press the Insert Vout reading in active cell button This will insert the PGA309 output reading from the ADS1100 This spreadsheet page provides for error calculations at two different power supply voltages The initial supply is Vs 4 963V you need to enter your measured Vs generate_sim_values xls PG...

Page 83: ...tric systems Connecting a 53kΩ resistor between the 3V pin and the center pin on JA will cause the power supply to shift from 5V to 4 5V You can adjust the value of the shunt resistance to get more or less power supply deviation A short will cause the power supply to deviate from 5V to 3V Vout ADJ GND Vin Vin NC EN Vout 53k 3V JA 5V JA JB JF JC JD JE VOUT 5V PROG 3V PC 1PU INPU ON SDN RTS DTR DIS ...

Page 84: ...SBOA103C Jan 2006 PGA309 Quick Start System Reference Guide 84 Make sure that you measure the supply voltage Vs and enter it into the PGA309 Designer s Kit Control Program ...

Page 85: ...it into the PGA309 Designer s Kit Control Program Measure the PGA309 post calibration error at a different supply voltage to see the affect of PSR on error For this example the supply was changed from Vs 4 963V to Vs 4 457V and the average error changed from 0 06 to 0 03 generate_sim_values xls PGA309 Ratiometric Error Tab ...

Page 86: ...is used to get an output swing beyond the range of the PGA309 The circuit shown below is a typical example of gain scaling with an offset shift The PGA309 calibration spreadsheet can accommodate external gain and offset scaling Doing the calibration by measuring the output of the external gain stage will calibrate out errors caused by resistor tolerance in the external stage R1 R2 Rf Vref Vo PGA30...

Page 87: ...factor for the spreadsheet ExtraOffset 0 5 ExtraOffset Rf 10 10 3 ExtraGain 2 5 ExtraGain Rf R1 Rf R2 1 For the spreadsheet you need to break the function into extra gain and extra offset as shown below Rf 5000 Substitute the value of R2 into equation 2 to solve for Rf R2 5000 Substitute equation 2 into equation 3 and solve for R2 Equation 3 Vin 4 5V Vo 10V 10 Rf 10 10 3 Rf R2 1 4 5 Rf 10 10 3 2 5...

Page 88: ...tem Reference Guide 88 PGA309 With Output Scaling 0 to 10V PGA309 Calibration Spreadsheet Sensor Curvefit Tab The ExtraGain and ExtraOffset factor are entered here on the spreadsheet Normally these are set to ExtraGain 1 0 and ExtraOffset 0 0 ...

Page 89: ...ick Start System Reference Guide 89 PGA309 With Output Scaling 0 to 10V PGA309 Calibration Spreadsheet Sensor Curvefit Tab The data that is measured at the output of the external amplifier is entered directly into the spreadsheet ...

Page 90: ...erence Guide 90 PGA309 With Output Scaling 0 to 10V The output range must be include the scaling stage PGA309 Calibration Spreadsheet Calibration Results Tab Other then these few minor changes the calibration method is the same as the other examples ...

Page 91: ...Guide 91 Iout Iin Iref 100 Iout Vin R1 Vref R2 100 Iout 100 R1 Vin 100 R2 Vref Iout ExtraGain Vin ExtraOffset 2 5 The spreadsheet can also be used to calibrate a system using a PGA309 with a 4mA to 20mA output scaling PGA309 With Output Scaling 4mA to 20mA ...

Page 92: ...for R1 R1 25 10 3 For the spreadsheet you need to break the function into extra gain and extra offset as shown below Iout 100 R1 Vin 100 R2 Vref Iout 100 25 10 3 Vin 100 125 10 3 2 5 Iout ExtraGain Vin ExtraOffset 2 5 Iout 4 10 3 Vin 800 10 6 2 5 This calculation shows how the example configuration shown on the previous page can be used to take the 0 5V to 4 5V output of the PGA309 and re scale it...

Page 93: ...m Reference Guide 93 The ExtraGain and ExtraOffset factor are entered here on the spreadsheet Normally these are set to ExtraGain 1 0 and ExtraOffset 0 0 PGA309 Calibration Spreadsheet Sensor Curvefit Tab PGA309 With Output Scaling 4mA to 20mA ...

Page 94: ...ystem Reference Guide 94 The data that is measured at the output of the voltage to current converter is entered directly into the spreadsheet in Amps PGA309 Calibration Spreadsheet Sensor Curvefit Tab PGA309 With Output Scaling 4mA to 20mA ...

Page 95: ... Guide 95 The output range must be include the scaling stage in Amps Other then these few minor changes the calibration method is the same as the other examples PGA309 Calibration Spreadsheet Calibration Results Tab PGA309 With Output Scaling 4mA to 20mA ...

Page 96: ...al communication line is connected to the Vout pin When the PGA309 is initially powered up the Vout pin is placed in a high impedance mode for 15mS If communication is established using the One Wire during this time the PGA309 will keep Vout in high impedance until the communications is complete After the communication is complete the PGA309 Vout pin will become active and remain active until powe...

Page 97: ...SBOA103C Jan 2006 PGA309 Quick Start System Reference Guide 97 PGA309 In Three Wire Mode If the Set PreCal EE feature is used the test pin is normally grounded leave PGA309 Test Pin HIGH box unchecked ...

Page 98: ...nto test mode The main benefit of test mode is that the Gain DAC and Offset DAC are forced to remain at the last values written to their respective registers In the case of three wire mode the test pin is grounded and cannot be used In this case an EEPROM table can be built that will force that Gain DAC and Offset DAC to be constant The PGA309 Designers Kit Control Program Set Precal EE feature si...

Page 99: ... 2006 PGA309 Quick Start System Reference Guide 99 PGA309 In Three Wire Mode When using this feature first set all the registers to values your application requires Then press the Set PreCal EE button Step 1 Step 2 ...

Page 100: ...erifies the value of the Zero DAC and Gain Dac you want in your EEPROM configuration After creating the EEPROM table the PGA309 Designer s Kit Control Program is ready for to be used with the calibration spreadsheet After pressing Generate and Write EEPROM Table the lookup table will be updated to force a constant Gain Dac and Zero Dac for PreCal settings ...

Page 101: ...SBOA103C Jan 2006 PGA309 Quick Start System Reference Guide 101 ...

Page 102: ...tute a license from TI to use such products or services or a warranty or endorsement thereof Use of such information may require a license from a third party under the patents or other intellectual property of the third party or a license from TI under the patents or other intellectual property of TI Reproduction of information in TI data books or data sheets is permissible only if reproduction is...

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