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ADS1282EVM-PDK: Input Range issue

Steve Widener
Genius 11010 points

Part Number: ADS1282EVM-PDK

. I was wondering if you could help us figure why we can’t get our data values to output proper values. Anytime we use a voltage input greater than 0.8V into the J6 header the data monitor hits its maximum data limit. I am familiar with the max and min input range for this ADC referencing this:

 

And have concluded that our input voltage range should been from -4.3V ~ 3.75V (using the specs specified below) with a typical value of around +/- 0.625. But as you can in our data table below, we don’t get near that range (current input range -0.8 ~ 0.8).

 

Here are the current values we are getting from the data monitor:

 

*Currently using unipolar configuration

*AVSS = 5.199V

* DGND = 0V

* AVDD = 5.190V

*DVDD = 3.300V

*All J7 jumpers are on

 

Voltage Ref: External 1.2V

Voltage Ref: External 1.2V

Input: 0V

-1090928

FFEF5A90

Input: -0V

-1153262

FFEE6712

-1067467

FFEFB635

-11774097

FFEE15AF

-1077973

FFEF8D2B

-1197819

FFEDB905

-1102895

FFEF2BD1

-1179519

FFEE0081

-1094360

FFEF4D28

-1154670

FFEE6192

-1068780

FFEFB114

-1171032

FFEE21A8

-1074702

FFEF99F2

-1196695

FFEDBD69

-1102394

FFEF2DC6

-1184184

FFEDEE48

-1100950

FFEF336A

-1156698

FFEE59A6

-1073753

FFEP9DA7

-1163557

FFEE3EDB

-1072652

FFEFA1F4

-1192079

FFEDCF71

Input: 0.2V

-1061823

FFEFCC41

Input: -0.2V

-1169758

FFEE26A2

-1078105

FFEF8CA7

-1159482

FFEE4EBC

-1103108

FFEF2AFC

-1129783

FFEEC2C9

-1091360

FFEEf8E0

-1136578

FFEEA83E

-1068282

FFEFB306

-1164598

FFEE3ACA

-1075273

FFEF97B7

-1162013

FFEE44E3

-1100527

FFEF3511

-1132328

FFEEB8D8

-1095079

FFEF4A59

-1131134

FFEEBD82

-1067904

FFEFB480

-1161932

FFEE4534

-1071183

FFEFA7B1

-1167873

FFEE2DFF

-1096470

FFEF44EA

-1139494

FFEE9CDA

Input: 0.4V

258221861

F642725

Input: -0.4V

-324104934

ECAE8D1A

257950880

F6004A0

-323996059

ECB03665

258064287

F61BF9F

-324229655

ECACA5E9

258315776

F659600

-324373393

ECAA746F

258307005

F6573BD

-324159303

ECADB8B9

258069002

F61D20A

-323999635

ECB0286D

258012790

F60F676

-324214322

ECACE1CE

258343050

F66008A

-324370157

ECAA8113

258425308

F6741DC

-324185569

ECAD521F

258006917

F60DF85

-323985999

ECB05D81

257949568

F5FF80

-324152972

ECADD174

Input: 0.6V

593933855

2366B61F

Input: -0.6V

-706349229

D5E5F753

593973093

23674F65

-706615027

D5E1E90D

594319988

236C9A74

-706642630

D5E17D3A

594572081

23707331

-706642630

D5E62A08

594398816

236DCE60

-706280828

D5E70284

594058587

23689D58

-706596272

D5E23250

594164902

236A3CA6

-706676453

D5E0F91B

594466163

236ED573

-706416934

D5E4EEDA

594355078

236D2386

-706287793

D5E6E74F

594023458

23681422

-706523073

D5E3503F

594023458

2368A4FD

-706699527

D5E09EF9

Input: 0.8V

917194871

36AB4877

Input: -0.8V

-1009848562

C3CEEF0E

916822533

36A59A05

-1010003859

C3CC906D

916860306

36A62D92

-1009718443

C3D0EB55

917213428

36AB90F4

-1009525245

C3D3DE03

917148132

36AA91E4

-1009770633

C3D01F77

916756075

36A4966B

-1009983572

C3CCDFAC

916709736

36A3E168

-1009780153

C3CFFA47

917026313

36A8B609

-1009507405

C3D423B3

917026313

36AB49BB

-1009695849

C3D14397

917182907

36A59397

-110010259

C3CC776E

916820887

36A33A21

-1009830873

C3CF3427

Input: 0.9V

1073741823

3FFFFFFF

Input: -0.9V

-1073741824

C0000000

1073741823

3FFFFFFF

-1073741824

C0000000

1073741823

3FFFFFFF

-1073741824

C0000000

1073741823

3FFFFFFF

-1073741824

C0000000

1073741823

3FFFFFFF

-1073741824

C0000000

1073741823

3FFFFFFF

-1073741824

C0000000

1073741823

3FFFFFFF

-1073741824

C0000000

1073741823

3FFFFFFF

-1073741824

C0000000

1073741823

3FFFFFFF

-1073741824

C0000000

1073741823

3FFFFFFF

-1073741824

C0000000

1073741823

3FFFFFFF

-1073741824

C0000000

1073741823

3FFFFFFF

-1073741824

C0000000

  • +1
    TI__Mastermind 46380 points

    Hello Steve,

    If using unipolar mode, then AVDD=5V and AVSS=0V.  AVSS cannot be set to 5V as shown above; not sure if this is a typo or the voltage that has been applied to the EVM board.

    Also, with a reference voltage of 1.2V, the maximum full scale input will be +/-0.6V when using a PGA gain of 1.  Since the data max is 3fffffff and c0000000, I assume the SINC filter output is being used.  In this case, you should get 3fffffff with an input differential voltage of +0.6V and c0000000 with an input differential of -0.6V.

    The absolute range is the common mode input range of the ADC referred to ground.  This is not the maximum differential input voltage, which is lower.  The maximum voltage on the AINP and AINN pins with respect to ground (AVDD=5V and AVSS=0V) will then be +0.7V to +3.75V.  The difference between these two inputs is the full scale input range of +/-0.6V.  A typical common mode voltage would be +2.5V.  For positive full scale input voltage of +0.6V, AINP=2.8V, AINN=2.2V.  For negative full scale input voltage of -0.6V, AINP=2.2V and AINN=2.8V.  In all cases, all voltages applied to the input pins are positive voltages with respect to ground when using unipolar supply configuration.

    Regards,
    Keith Nicholas
    Precision ADC Applications