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AD7193 Supply Voltage & Reference

SCHEMATIC1 _ PAGE1.pdf

Hello,

Please find attached figure.

I have used REFIN2 by setting REFSEL=1.

As shown in fig. 3.3V supply is connected to AVDD & REFIN1 is tied to AVDD. Fig. shows Inductor L is connected in series. Instead of L if I Connect Resistor 10K then voltage at point A=1.618V. I tried with R=10k,R=100K & R=1M... in all cases i got voltage at point A=1.618V..

i am interested to know why this voltage drops & why it is same for all three values of 10K, 100K & 1M... in case of Inductor voltage at point A=3.3V..

  • Hi, Latika.

    So the REFIN1+ is disconnected internally when you measure the voltage at Node A? How about when you selected REFIN1 as your reference? Have you seen the same voltage drop? However, excessive RC source impedance is not recommended on the reference input as this is unbuffered.

    Thanks,

    Jellenie

  • Hello mam,

    REFIN1+ is disconnected internally & REFIN2+ is selected via REFSEL=1.

  • Hi,

    So REFIN1+ is floating? Have you tried to select REFIN1 instead and check if you are seeing the same results?

    Thanks,

    Jellenie

  • Hi...

    Previously i have connected 2.5V to REF1IN+ & selected REF1IN+ by setting REFSEL=0;  in that case i am getting this as 2.5V

  • Hello mam,

    With respect accuracy issue thread now i am facing another issue...

    I want to measure this 13mV differential signal proportional to velocity....

    When i apply input from simulator i get stable result but now i am going to test it with actual velocity input ADC counts stable for lowest range & starts Suddenly varying at highest rang.

    for e.g:

    AIN8 is connected to fixed 1.25V

    AIN7 is connected to 0 - 13mV signal with 5.74Hz frequency which is override on 1.25V dc signal...

    So the overall signal look likes a differential signal..

    My input signal is 0.556813mV full scale....Connected to AIN7

    so the calculated full scale counts for 0.556813mV with gain=128, ref=2.5,bipolar mode=239149

    i/p          (%) i/p      (mV) Calc. ADC   Counts  ADC Counts (Min) ADC Counts (Max) Difference (Count Variation )
    100% 0.556813 239149.3 208114 270184 62070
    75% 0.41761 179362 178009 180715 2706
    50% 0.208805 89680.98 88332 91030 2698
    25% 0.139203 59787.32 59399 60176 777
    0% 0 0 658 1069 411

     Please refer above result at full scale range 0.556813mV in above table ADC counts Varies between 62070 Such large variation is not Acceptable...

    With the same condition if i reduce i/p to 75% 0.41761mV in above table Count Variation reduces to 2700 Counts which is Acceptable since.

    Similarly Count variation reduces with input....

    Please Suggest what can i do to Stabilize the ADC counts.. The Max  Possible signal in my case is 1.312mV....

  • Hi,

    When you connected 2.5V is that the same circuitry that you applied? I would say that you could have voltage drop across the resistor but since the REF1IN+ is floating, the output at node A is unreliable. When the REFIN1+ is selected as reference, and you have a series resistor with it, then the voltage drop across the resistor can be define by the reference input current and also the AVDD supply current range. So, I would suggest not to put any high value resistor in series with the supply to avoid any voltage drop. 

    Thanks,

    Jellenie

  • Hi, Latika.

    Regarding the accuracy thread, I would suggest to discuss this on that thread or create a new thread for this to avoid any confusions.This is just to help others to easily tracks the same issue.

    Thanks,

    Jellenie

  • Hi....

    I have connected Resistor instead of inductor just for trial purpose since my ADC counts are not stable...

    Now i have reconfigure my circuit with AVDD applied to REF1IN+ via Inductor so voltage at node A=AVDD=3.3V... & REF2IN is Selected By REFSEL=1 & 2.5V reference is applied at REF2IN+...

  • Okay, good to hear that you have re-configured the schematic properly.

    Thanks,

    Jellenie