AD7193 Supply Voltage & Reference

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

 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