Electronics > Beginners
Interfacing with TI ads1278 ADC with Cyclone IV FPGA
rsridhar:
Hi All!
Im trying to get my Altera FPGA to talk with a TI ads1278 ADC:
http://www.ti.com/lit/ds/symlink/ads1274.pdf
This is my first time trying this; and Ive only ever used my FPGA with a much simpler ADC. But Id like to get this fancy Delta/Sigma one up and running.
I put together what I thought would get the adc up and running, but all I got was my ADC getting really hot; and outputting a constant "0". So something is wrong. I have some very basic questions as this is my first ever time using this adc:
1. The ADC has lots of repeat pins; for example there are 5 analog gnds, 4 analog power supplys, 4 Digital Gnds, 4 Digital power supplys. Do all of these need to be connected? Or is connecting one sufficient?
2. What is the difference between Analog gnd and Digital Gnd? Is there any advantage in setting them differently?
3. There is an Analog power (4.7-5.25V); a Digital power supply (1.65-3.6V). But what about the following pins, do they need to be connected:
-VCOM AVDD/2 Unbuffered voltage output
-VREFN Analog input Negative reference input.
-VREFP Analog input Positive reference input.
-DVDD Digital power supply Digital core power supply
4. Overall, if you look at the timing plot on page 8 for the SPI interface; I am setting Drdy low every 512 clock cycles (using High Resolution mode, so Fsample/Fs=512). Is this correct?
5. I am using a housing which takes the ADC package and converts it to dip switches. Im using jumper cables to connect the dip switches on the ADC adapter to DIP pins, which Im using jumper cables to connect to the FPGA's pins. The adapter looks like this:
https://www.ebay.com/i/172825294343?chn=ps
Any possible issues with this adapter? My signals are running at a max of 25MHz through the cables conecting them; the cacbles are all under 6".
6. Is the sigma delta ADC supposed to get this hot? it smells like it may start melting; but I may have had it connected incorrectly.
Thanks, Id apreciate any guidance on this!
KaneTW:
1) Unless specified otherwise, they all need to be connected (to the right voltages respectively)
2) If you have a separate ground plane for analog and digital, tie them together at the ADC. It's a complicated topic, and usually fine to use the same ground unless you need the performance.
3) IOVDD needs to be within 1.65-3.6V, DVDD depends on the frequency you run the ADC at, check the datasheet.
VCOM is an output pin for AVDD/2, VREFN/P is for connecting a reference voltage. Specifically, this ADC doesn't seem to have an internal reference, so connect it to an appropriate voltage reference (check data sheet).
4) You're not supposed to set DRDY low. DRDY is an output pin that indicates that a reading is available.
5) You'll probably run into SPI issues at higher speeds without proper termination even with relatively short cable length.
6) It dissipates 800mW at most in high-speed mode, so depends. If you're putting a too-high voltage on DVDD you might be frying the ADC.
rsridhar:
--- Quote from: KaneTW on July 07, 2018, 06:13:53 pm ---1) Unless specified otherwise, they all need to be connected (to the right voltages respectively)
2) If you have a separate ground plane for analog and digital, tie them together at the ADC. It's a complicated topic, and usually fine to use the same ground unless you need the performance.
3) IOVDD needs to be within 1.65-3.6V, DVDD depends on the frequency you run the ADC at, check the datasheet.
VCOM is an output pin for AVDD/2, VREFN/P is for connecting a reference voltage. Specifically, this ADC doesn't seem to have an internal reference, so connect it to an appropriate voltage reference (check data sheet).
4) You're not supposed to set DRDY low. DRDY is an output pin that indicates that a reading is available.
5) You'll probably run into SPI issues at higher speeds without proper termination even with relatively short cable length.
6) It dissipates 800mW at most in high-speed mode, so depends. If you're putting a too-high voltage on DVDD you might be frying the ADC.
--- End quote ---
Thanks, Ill make these fixes and see if I cant get this thing up and running! Cheers!
rsjsouza:
One additional detail: take a look at the development kit documentation for an example of a fully working PCB and electrical diagrams.
http://www.ti.com/tool/ADS1278EVM-PDK
james_s:
If it got so hot that it smells, then it is probably ruined. I would start by figuring out what you connected backwards or to the wrong voltage.
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