sorry for again troubling you....but i have a query regarding the REFIO pin in the Chip ADS8558 so i thought of continuing in this thread only....i am using the internal reference and so i have enabled the REFen/WR pin but in this case the range mentioned on the REFIO pin is 0.5 volts to 3.025v. Is it possible to check what voltage am getting on the REFIO pin?? as in i saw the voltage on multimeter and it showed me 4 volts. Am i doing anything wrong here??? i am getting the output on the parallel data bus but not very accurate...and i know that the output data has direct relation with the reference.
No bother at all! I will assume that you are running the ADS8558 in hardware mode. In that case, you can only get 2.5V on the REFI/O pin. Try looking at REFIO with an oscilloscope and let us know what you see. The caps recommended in the data sheet have to be close to the pins of the part, so this may be part of the problem.
If you are still using the coupon board you found in your original post, please double check all of your connections. The HW/SW pin needs to be grounded. Please also double check that you have all the device GND pins (AGND and BGND) tied together.
Yes i am using in HW mode and i have grounded it properly. I have tied AGND to BGND as in i am having common ground. I did check it on a oscilloscope and i am getting a sine wave having pk-pk voltage 2V. Is this output modulated one as in if i put a capacitor of some another value will it affect the output on REFIO pin???
My second doubt is that i want to use the ADC for range of 0 to 5 volts. So it should be better to give 5 Volts External to the REFIO pin, Am i right over here??? And yes i am using expansion board which i specifically made for mounting the LQFP package which is sort of similar to DIP package as shown in Proto-type site.
You need to add a cap for the reference to be stable. The ADS8558 cannot accept a 5V reference - the input to REFin would need to be under the 3.025V level. The analog input of this device is bi-polar, so you would only be using half the available input range running with 0-5V on the input. Please see the Analog Inputs section of the data sheet on page 23.
Yes i have added a CAP there but not of the value specified in datasheet i will add that by tomorrow and yes i got the point....thank you :)
I did add the CAP and i have kept RERen pin as high which means that am using internal 2.5 volts. My input range is 0-5volts,as you said its half of the total range. Like in many ADC ref voltages sets the range as in the output range for example if i give ref as 2.5 volts than step size would be 2.5/2^12 or if i give 5 volts it will be 5/2^12 and max input would be 2.5 or 5 for the above mentioned cases, i hope i am right here, In this case i am having 2.5volts as ref and my input is from 0-5volts my only doubt is that how will the output react as in i am trying to find a relation between ref voltage, my input range and the output??
On the ADS8558, pin 27 controls the input range. It's going to be either +/-2 * Vref (RANGE pin = 1) or +/-4 * Vref (RANGE pin = 0), so thats +/-5V or +/-10V. Assuming you have that pin high, your lsb size is 10V/4095.
Thanks a tonne got it.....
I have connected Refen pin to ground and i am giving 2.5 volts external to REFIO pin. Initially i used to use internal 2.5 volts reference. For the time being i am using A0 channel only, and am giving pulse to Rd and Conv_a pins using switches (CS pin is always grounded). I used to get the output initially but since i have connected REFIO pin external 2.5 volts i am not getting the output. I have tied both the grounds. I have grounded har/sw pin also the par/ser pin. Can you think of anything which i am missing over here???. I have also connected STBY pin to BVDD.
Range = BVDD
Word = BGND
HVSS = -5Volts
HVDD = 5Volts.
The capacitors are connected as per the datasheet.
I am giving high pulse to COnv_a first and then lowering the RD pin to get the output..
My appologies for the delay in getting back to you - please try and monitor your CONVST impulse with a scope. You may be putting the ADC channel in partial power down mode which could happen if your switch is giving any 'bounce' to the input signal. Verify the CONVST against the BUSY signal and see if there are any transitions that the ADS8558 might interpret as a secondary CONVST input while BUSY is high. If this is the case, you will need to toggle the RESET pin or cycle power to the ADS8558.
I have got the parallel output of all the six channels and my range is from -2Vref to +2Vref where Vref is internally supplied. Now the next task is to interface ADC with Virtex2pro FPGA. I am thinking of using a DCM and lowering clock so that i can give pulse to Conv_x pin and taking the parallel output on FPGA I/O pins.Will this strategy work out? If not than can you suggest me some material or files from where i can get information regarding this.
It should work, I can't think of anything off the top of my head that might pose a problem. We don't have anything readily available for the Virtex2Pro, the EVM we have for the ADS8568 uses the Spartan family (we use the XEM3010 from OpalKelly). We can provide you our source VHDL if you think that might help.
Thanks, I will try that soon. Yes it would be better if you could provide me with source code. That might help me get started on this. My email address is firstname.lastname@example.org
Thanks a lot
You should receive the information you requested in an email shortly.
Hardware and Software Platform Development
Precision Data Converters
Thanks for the code...I have made one using VHDL and am seeing the output on a MSO. Can i post/mail the code and the output and can you verify it if it is possible?.
Sorry for troubling you again but i am planning to write device driver in linux for ADS8558. Can you please send me the addresses of the registers/hardware module?. And on the same note i am also trying to write device driver for DAC7724 can you please send me the addresses of the registers of the DAC too?
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