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ADS1294R: LOFF register current mode and pullup or pulldown resistor mode difference

vivek yuvan
Prodigy 190 points
Part Number: ADS1294R

Dear   Friends 

 I have configured register LOFF as a current mode so I get the ECG waveforms but I changed pullup or pulldown resistor mode in LOFF register I didn't get the valid waveforms, sometimes lead1 data only coming what

do I do we do for valid waveforms in pullup or pulldown resistor mode?

and one more clarification in the current mode magnitude 6NA, 12NA,18NA, and 24 NA I don't know what is the difference between this and all...

  • 0
    TI__Guru 57296 points

    HI Vivek,

    Thank you for your post.

    The resistor pull-up or pull-down lead-off method will generate a larger current magnitude than the lead-off current sources (approximately [AVDD-AVSS] / 10M). Most likely, the impedances in your signal path, including the electrode-skin contact impedance, is producing a large DC offset voltage in the presence of the lead-off current. This can rail the output of the PGA. Is the ADC output reading full-scale?

    You could try reducing the gain of the PGA to see if that brings the voltage to within range. If you cannot tolerate the large offset voltages even with smaller gain, then you must reduce the lead-off current or improve the contact quality of the electrodes.

    Best Regards,