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ADS1298: Not able to Read differential voltage on ADS1298.

Part Number: ADS1298
Other Parts Discussed in Thread: MSP430F67651,

Hello,

I am using ADS1298 with MSP430F67651. 

I am doing measurement successfully with ADS1298 when i connect my DC voltage upto 2.4V on INP and GND to INN.

But in my application i need to read differential voltage across a resistance as in below circuit , with this input the ADS1298 is not coverting data.

Please give me suggessions. I have measuring this differential voltage on SD24 ADC of MSP430F67651 and it is working correctly, but not on ADS1298. Please help.

  • Hi Ashish,

    Thank you for your post.

    The absolute voltage on each pin is limited by the analog supplies. The absolute differential voltage must be less than Vref / Gain. In addition, the PGA common-mode has a limited input range as well.

    Please consult the data sheet and confirm that you are satisfying these requirements.

    Best regards,
    Ryan
  • Hello Ryan,

    Thanks for reply,

    I am doing measurement on SD24 channel of MSP430F67651 MCU and providing inputs like i attached drawn circuit.And it is measuring difference of A and B,i.e., 0.5 mV.

    the datasheet of  MSP430F67651 shows as below:

    Now when i connect same Input to ADS1298, it is not doing the same whereas the datasheet is showing same ratings of it's ADC as SD24 of MSP430.

    Additionally if i reduce the input voltage from 3.6V to 2 Volt DC and in that case the difference of voltage across 50ohm is not getting measured by ADS1298.

    while when i connect INN to GND and measure 0.5mV, it is measuring it successfully.

    FYI...my AVDD to ADS1298 is 3.3VDC.

    Que: Is the ADS1298 do not work in 'Bipolar mode' same as SD24 in MSP430???

     

    Regards,

    Ashish Jain

  • Hello Ashish,

    The Absolute Maximum Ratings are not intended for normal operation. Please use the Recommended Operating Conditions and the Electrical Characteristics tables for acceptable device input ranges and conditions.

    What is the analog supply voltage on the ADS1298? If you are using a unipolar 3-V or 3.3-V supply, then the positive input (voltage A) will exceed the positive supply (AVDD). Also, the PGA input common-mode range will be violated as well. In this case, the differential input voltage of 25.71 uV is perfectly acceptable, but the common-mode and absolute voltages are out of range.

    Best regards,

  • Hello Ryan,

    Thanks for reply, 

    I have tried lower voltage as 2 volts in place of 3.6 in above circuit and the ADS1298 is still not reading the differential voltage.

    But as i told you the SD24 channel of MSP430 is able to read the same.

    please read my previous message where i mentioned a Question for you with datasheet screenshots that

     Is the ADS1298 do not work in 'Bipolar mode' same as SD24 in MSP430???

     

    Thanks and regards,

    Ashish Jain

  • Hi Ashish,

    The ADS1298 can accept both unipolar and bipolar power supply configurations. Notice that the requirements for min/max absolute input voltage as well as the input common-mode voltage are both written in terms of AVDD and AVSS.

    Regards,