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ADS1120-Q1: Current Measurement using ADS1120

Vaithieswaran S
Prodigy 50 points
Part Number: ADS1120-Q1

Hey Matt.

Its been long while .. What's up.. How are you ?? I have been using the ADS1120-Q1 for my current measurement . I have tried with the two different register 2 configuration. One with the VREF as : Analog supply (AVDD – AVSS) used as reference (In the hardware we have given 5V to AVDD pin and AVSS as ground ) and other with the External reference selected using dedicated REFP0 and REFN0 inputs and in the REFP0 given as 5V and REFN0 as GND .

The value for the register are VREF as Analog supply {0x43,0x81,0x04,0xD8,0x00} and

VREF as External Reference {0x43,0x81,0x04,0x58,0x00}.

We have made the measurement with the hall sensor output using 6 and half multimeter but when i try to read the ADC output value with MSB first and LSB second. Below are the tabulated values .When i put the calculation for my cross verification with hall sensor output I'm getting only half of the value. We have made with different current values .

Formula used : actual value = (ADC Value - 32780) --> The offset value we got by shorting the positive and negative terminals of AVDD and AVSS value #32780(0x8000h)

Software Hall sensor output = (actual value * 5000) / 32767; (5000 for 5V as Ref voltage )


During Discharging

Load MSB LSB Decimal Value Decimal value - offset Hall sensor output Software Hall sensor output
No Load 0x8f 0xfd 36861 4081 1.247 622.7301859
1A  0x90 0x1b 36892 4112 1.256 627.4605548
2A 0x90 0x3c 36924 4144 1.266 632.3435163
3.5A 0x90 0x6d 36978 4198 1.281 640.5835139


During Charging

Load MSB LSB Decimal Value Decimal value - offset Hall sensor output Software Hall sensor output
1A  0x8f 0xda 36822 4042 1.247 616.7790765
2A 0x8f 0xbc 36796 4016 1.256 612.8116703
3A 0x8f 0x9c 36764 3984 1.266 607.9287088
4A 0x8f 0x7d 36734 3954 1.281 603.3509323
5.03A 0x8f 0x5c 36700 3920 1.281 598.1627857


Kindly help Matt and guide for further. Whether its is correct or not and why I'm getting only half of the hall sensor output. and let me know if the register value are anything needs to be corrected

  • 0
    TI__Guru**** 173426 points

    Something with your formula seems off.  Why does the Hall produce the same value (1.281) at 3.5A discharge and 4A, 5.03A during charging?  Can you share a schematic please?

  • 0 in reply to Tom Hendrick
    Prodigy 50 points

    Dear Tom ,

    Below are the actual and correct values of Hall sensor during charging and discharging.

    During Discharging

    Load MSB LSB Decimal Value Decimal value - offset Hall sensor output Software Hall sensor output
    No Load 0x8f 0xfd 36861 4081 1.247 622.7301859
    1A  0x90 0x1b 36892 4112 1.256 627.4605548
    2A 0x90 0x3c 36924 4144 1.266 632.3435163
    3.5A 0x90 0x6d 36978 4198 1.281 640.5835139

    During Charging

    Load MSB LSB Decimal Value Decimal value - offset Hall sensor output Software Hall sensor output
    1A  0x8f 0xda 36822 4042 1.234 616.7790765
    2A 0x8f 0xbc 36796 4016 1.227 612.8116703
    3A 0x8f 0x9c 36764 3984 1.217 607.9287088
    4A 0x8f 0x7d 36734 3954 1.208 603.3509323
    5.03A 0x8f 0x5c 36700 3920 1.198 598.1627857

    Whether its is correct or not and why I'm getting only half of the hall sensor output. and let me know if the register value are anything needs to be corrected

  • 0 in reply to Vaithieswaran S
    TI__Guru**** 173426 points

    Please clarify your registers, are we to assume  {0x43,0x81,0x04,0x58/D8,0x00} refers to registers {0, 1, 2, 3, ?}?  Register 2 is where the reference voltage is set and if you are actually sending 0x04 to register 2 then you only have 2.5V reference.

  • 0 in reply to Tom Hendrick
    Prodigy 50 points

    Dear Tom,

    Below is the format which I'm referring { Write register value , Reg0,REG1,REG2,REG3} 

    So for REG2 we are configuring the value as 0x58 / 0xD8 

  • 0 in reply to Vaithieswaran S
    TI__Guru**** 173426 points

    Thank you for clarifying.  With AINn tied to AVSS and VREF = 5V, your LSB size would be 305uV.  With your offset corrected values above this would give you the following results:

    4081 1.2447
    4112 1.2542
    4144 1.2639
    4198 1.2804