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ADS125H02: ADC single end configuration

sai devaraj m
Intellectual 340 points
Part Number: ADS125H02

Hi,

  I'm currently working on ADS125H02 interfacing with MSP432p4111. In this i connected the analog pins a follows,

AIN0 - input voltage 

AIN1 - Ground

AINCOM - ground

Is this analog pin connection is good for Single end operation (i.e i give 1V to AIN0 to get digital out).

and if i get any hex value in MSB, MID, LSB how to calculate to know the voltage value. Is there any formula to calculate.

Although i'm having the given adc calculation calculator it is only for differential calculation i think so.

So, please help me out with this.

Thanks in advance. 

  • 0
    TI__Mastermind 35111 points

    Hi Sai,

    The output coding remains the same whether you apply a differential signal or a single-ended signal. The ADC always treats the input as differential, measuring between AINP and AINN. So it does not care if AINN = 0V, or some other value.

    The ADS125H02 using a bipolar coding scheme that is explained in Table 15 on page 47 in the datasheet. Since the coding scheme is bipolar and you are applying a single-ended signal, then you can only use half of the code range.

    To convert output code to voltage, you would take the hex/binary ADC output, convert to decimal, and multiply by 1 LSB. This gives you the voltage that corresponds to that output code. Please note that 1 LSB depends on the reference voltage and the gain setting you choose

    -Bryan

  • 0 in reply to Bryan Lizon86
    Intellectual 340 points

    Hi Bryan,

         Yes, I used the same calculation. But if i give 1V as an input, I'm getting 1.5V or 2V as an output as per the calculation. Is there anything I'm missing. Please help me out with this.

    Thanks in advance.

  • 0 in reply to sai devaraj m
    TI__Mastermind 35111 points

    Hi Sai,

    What gain are you using, what is your differential VREF voltage, and what are the output codes you are receiving from the ADC?

    -Bryan

  • 0 in reply to Bryan Lizon86
    Intellectual 340 points

    Hi,

    I'm using 0.5 gain and internal reference.

    I gave 1V analog input and I'm getting 

    MSB - 5A

    MID - 3E 

    LSB - 11

    are the output values

    and calculated using the formula as mentioned above by you.

    Thanks in advance.

  • 0 in reply to sai devaraj m
    TI__Mastermind 35111 points

    Hi Sai,

    Can you read back the full register map from the H02, then immediately after the register read back can you take 10 data points with the 1V signal applied, and provide all of this information to me? The hex values you provided corresponds to ~3.52V using the settings in your last post, so something is wrong here.

    -Bryan

  • 0 in reply to Bryan Lizon86
    Intellectual 340 points

    Hi,

    I gave 1v in analog input and read 10 hex values and nothing matched with input.

    Also I need to know about the all three input pins ( AIN0, AIN1, AINCOM) connection.

    What is the default pin connection for these pins in single ended operation?

    Thanks in advance.

  • 0 in reply to sai devaraj m
    TI__Mastermind 35111 points

    Hi Sai,

    Can you please read back the full register settings, then take data, and then post the register values as well as the data output? I cannot help much when I don't know how the ADC is configured and I cannot see the data output.

    The default multiplexer setting is both pins shorted to VCOM ([HVDD-HVSS] / 2). You can measure between AIN1 and AIN0, AIN0 and AIN1, AIN0 and AINCOM, and AIN1 and AINCOM.

    -Bryan