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VREF Problem with ADS1298ECGFE-PDK

Benjamin Tan
Prodigy 130 points

Other Parts Discussed in Thread: ADS1298ECGFE-PDK, ADS1298

Hello,

I recently connected teh ADS1298ECGFE-PDK demo unit and trying to configure it to measure 0-4V.  I belive I have the ADS1298ECGFE Eval software configured correctly but when ever I take a reading, my mreasurement max out at 2.5 V.  I tooked at the TP3 (VREFP) and noticed that it was ~+1.5V (relative to AGnd) when the spec stated its should be +2.5V.  I measured VREFP reltative to VREFM (cathode side of C1 pad) and noticed that was the expected +4V.  Could I have misconfiguered something that might cause the VREFP at a voltage other than 2.5V.

 

Thank,

Ben

  • 0
    Prodigy 130 points

    I reviewed the Spec and noticed that my jumper was not in the correction position for JP24.  Changed it and that fixed everything.  Not sure how that happened though.  I would have expected all the jumpers to be in the correct position from the vendor but I guess that's why they have manuals.

     

    Thasnk,

    Ben

  • 0 in reply to Benjamin Tan
    TI__Guru**** 182801 points

    Thanks for letting us know Benjamin,

    We'll double check the test procedure for the boards and make sure the manufuacturing team is setting the jumpers correctly.

  • 0 in reply to Tom Hendrick
    Prodigy 130 points

    I'm trying to measure a signal from 0-4V using the ADS1298ECG-FE and internal VRef.  However, I am unable to generate the VRef of 4.0V using the supply voltage of 3.0 (AVDD to AVSS).  When using supply voltage of 3.0V and configured to get VRef of 2.4V, I get the expected 2.4V at VREFP to VREFN.  When I reconfigure to get 4.0V still using 3.0V supply, I get ~3.0V at (VREFP to VREFN).  Is the device capable of generating VRef of 4.0V with a 3.0V supply?  Would I have to change supply voltage to 5.0V by replacing U10 as suggested in Table 2 of manual (SBAU171) to generate VRef of 4.0V?

    Thanks,

    Ben

  • 0
    Intellectual 820 points

    Hello,

    Please carefully read datasheet for ADS1298 (SBAS459E, p.26) and take a look at ADS1298ECGFE schematics (SBAU171, p.67). Please note, that VREFP should be measured relative to AVSS, not relative to AGND in case when internal reference is used! ADS1298 successfuly generates +4V VREFP (relative to AVSS) while powered this way: AVDD=+2.5V, AVSS=-2.5V , DVDD=3.2V (relative to AGND). So the behaviour of ADS1298 in your case is absolutely normal: when measuring relative to AGND, you see only 1.5V, this is 4V+(-2.5V)[of AVSS rel. to AGND].

    Hope this will help you.

    Regards,

    Ilia V. Davidov