I m facing a problem with the use of the ad5791 evaluation board.
In fact, with this card I'm supposed to get an output voltage resolution of 1 LSB ( 20 µV), instead of this , when I increment the the 20 bit word with 1 LSB, nothing happens at the output voltage ,
The output voltage is updated only with 3 increments ( 3LSB = 60 µV) .
On the other hand, the INL error is indicated in the AD5791 datasheet to be less than 1 LSB. Here again, in our experiment and using the evaluation board its value is greater than 3lsb (60 µV)
Please Find attached the screen shot of the INL and the resolution steps we measured.
Could you please give me some helps , It will be appreciated.
What are the codes used to acquire the data in the screen shots? What reference and supply levels were you using? What load are you using at the output?
Which codes are written to the DAC? You might not be able to measure the difference if you are measuring with lower codes. Does this issue also appear when you are using higher codes?
any suggestions ?
Thank you in advance
I used the AD5791 EVALUATION BOARD and I interface it using an FPGA card from national instruments.
For the data acuisition, I used the 3458A Agilent multimetre with Labview.
Vrefp = 10V and Vrefn= -10V (I applied 5V to connector Vref).
Vcc = 5V
DGND = 0V
Vdd = +15V
I used the unbuffered output (Vout) and the "Control Register" is configured to 0x00010, in this case DAC output imedance is 3.4kohm. I got the same results with the buffered output (Vout_buf, output of the AD8675) when the "Control Register" is configured to 0x00012.
This issue apears in both lower and higher codes. I measured with codes between 0 and 1048576.