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Regarding ADS1230 Reference

Jayaraj A
Prodigy 200 points

Other Parts Discussed in Thread: ADS1230

Dear Sir,

          Referring the datasheet of ADS1230, I had taken the positive reference of ADS1230 directly from +5V_Analog & -ve Ref from AVSS, which all goes to my load cell. But your reference design consists a LPF of 100E, 100uF & 2.2uF in between AVDD & REFP+ and AVSS & REFN.

         Which is the right way to proceed? what are the advantages & disadvantages between the both?

         And I am using a one 10uF(ceramic X7R 5%) across my AVDD & AVSS, also one 10uF(ceramic X7R 5%) across my REFP & REFN. Will these values look okay? I am facing a drift of +/- 7 counts @ 15bit resolution only.

Experiments:

           I am using LM7805 as my 5V regulator. My digital & analog +5V & GND were isolated through 0E resistors.And I got one bulk electrolytic capacitor of 100uF/16V on my AVDD & AVSS line. If I mount a 10E resistor between DVDD & AVDD (0E on GNDs). I am finding sufficient improvement in my drift (3 count drift). So I  increased the resistor value to 27E & 47E, but poor result. What this indicates? (other than layout isse)

  Regards,

Jayaraj.A

  • 0
    TI__Guru** 113765 points

    Jayaraj,

    One of the issues with circuit design is how much circuitry is enough to get the job done.  The ADS1230REF design is robust and perhaps a little overbuilt.  You mention drift but it appears to me the issue is noise. 

    If you add a lot of filtering specific to the reference, you will get noise that is passed through the bridge and will be measured at the ADS1230 as noise.  This is because you will lose the ratio-metric feature of the measurement.  So the goal is to eliminate overall noise, but try to maintain the ratio-metric measurement.  So what do I mean by that?  Noise will be canceled in a true ratio-metric system.  But in reality there will be some phase delays that will not totally cancel.  So here is one reason why layout is important.  The ground return, for example needs to be very low inductance and should be a plane.  Ground traces are a source for noise pickup.  Cap placement may be more important than cap size.  So it is hard to give a full recommendation based solely on values.  The values you mentioned on a good layout should be sufficient.

    Best regards,

    Bob B