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ADS1293 voltage levels

Arnab Chakraborty
Intellectual 635 points
Other Parts Discussed in Thread: ADS1293

Hi


I have interfaced ADS1293 to EFM32 controller through SPI. Before giving ECG signal I am trying to give input dc voltage to input IN1 after routing it to channel 1. But whatever voltage I give at the input, I get attenuated voltage at the output by calculating the voltage from the formula provided in the datasheet. 

For example: If I give 100mv as input I get corresponding output for 45mv. If I give 150mv I get corresponding output for 65mv. Why this is the case? Please assist me..

Note: I tried the test mode provided in the datasheet without giving any input voltage. In that case the output is coming perfectly fine for all the channels of 0.2V.

Thanks

Arnab Chakraborty

  • 0
    TI__Expert 3835 points

    Hi Arnab,

    You need to connect IN1 to one terminal of channel 1, and IN2 to the other terminal of channel 1. For example IN1 to the positive and IN2 to the negative. You can choose to use other inputs or channel combinations as desired.

    Next you would apply a differential voltage between IN1 and IN2. In addition, the differential voltage should have a common-mode voltage such that your input signal is within the range of operation of the ADS1293.

    The common-mode voltage range (CMVR) is defined as:

    For VINmax = 400mV, the input common-mode voltage range is from 0.95 to VDD-0.95. If your differential signal is smaller, then the range can extend.

    The other extreme is VINmax=0mV... the CMVR becomes 0.25 to VDD-0.25.

    For example, apply 1.05V at IN1 and 0.95V at IN2. The differential voltage is +100mV and the common-mode is 1V.

    Regards,

    Sergio

  • 0 in reply to Sergio
    Intellectual 635 points

    Hello Sergio

    I tried the exercise suggested by you. Applied 1.05V at IN1 and 0.95V at IN2. But the o/p I got corresponds to 0v. The data register denotes 0x3FFFD8. 


    The error_range_ch1 denotes 00100101 in binary. Please refer the screenshot for your further reference.

    Thanks

    Arnab

  • 0 in reply to Arnab Chakraborty
    TI__Expert 3835 points

    Hi Arnab,

    What is your voltage supply and can you please share the contents of your registers? I am not sure why you are getting these errors.

    Thanks,

    Sergio

  • 0 in reply to Sergio
    Intellectual 635 points

    Hi Sergio

    I am giving a supply of 3.3V.. I am attaching the schematics..Please have a look....And which register contents you want?

    Thanks

    Arnab

    EXT-PWB-1184-CRL-EFM32-SCH_12082013_V16_0.pdf
  • 0 in reply to Arnab Chakraborty
    TI__Expert 3835 points

    Hi Arnab,

    I am interested in the values of the following registers at the time of measuring: 0x00, 0x01, 0x13, 0x19, 0x1A, 0x21, 0x22, 0x25, 0x2F, 0x37, 0x38 and 0x39.

    I would prefer to have the values of the complete register map, just in case I am overlooking a register in the list above.

    Thanks,

    Sergio