• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Subscribers 48 subscribers
  • Views 1598 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS8556 issues

cristiano martins
Prodigy 30 points
Other Parts Discussed in Thread: ADS8556, ADS7809

Hello everyone!

     I´m currently working with ADS8556 but I´m facing some issues. I tried to use it on both communications modes (SPI and parallel) with the same behavior. I already tried internal and external Voltage reference, and many others things but nothing change my problem: ADS8556 is giving to me the value converted with a lot of "noise" on converted samples.

     In other words, if I connect a signal on its input and watch the conversion results I found some "spikes" with more than 100 lsbs of amplitude. First picture below shows ground measuring. Second picture shows sinewave measuring.

 

 

I made a comparative with ADS7809 measuring same signal, using same power supplies, gnd etc. ADS7809 behave as expected but ADS8556 doesn´t.

Any ideas to solve this problem?

Thanks in advance!

Cristiano Moreira

  • 0
    TI__Mastermind 46290 points

    Cristiano,

    What hardware are you observing this on? Is it an EVM or a board of your own? If it's a board of your own please share a schematic & layout.

  • 0 in reply to Kevin Duke
    Prodigy 30 points

    Hi Kevin,

         I´m using my own boards. For tests and debugging I´m using a Explorer 16 (from Microchip) running with a PIC32MX795 (80MHZ) plus a PICTail board where the ADS8556 is placed. 

         The ADS8556 is soldered on a LQFP-DIP adapter with all ceramic capacitors soldered direct on adapter pins. Eletrolytic tantalum capacitors are soldered on PICTail with all the others components (input filters, linear regulators, etc). I also included 1N4148 diodes on HVdd and HVss pins to prevent any problems related to power sequencing.

         Everything works ok, I can use ADS on paralell and serial mode, for serial mode I tested daisy chain with 3 ADS8556, internal or external voltage reference, etc. I think I exploit almost everything on this AD converter and everything works, but in all cases the quality of sampled signal remains the same as sent in last post. 

         Now I have to solve this issue and design my final PCB including all the others stuff so, could you send me the gerber files of EVM board to guide me on this design? 

         Regards,

    Cristiano Moreira

    0550.ADS8556 + PIC.pdf

  • 0 in reply to cristiano martins
    TI__Mastermind 46290 points

    Cristiano,

    Attached are the gerbers. Hope this helps, if you need further assistance let us know.

    7127.6509747_ADS855X_GERB_A.ZIP

  • 0 in reply to cristiano martins
    Guru 20025 points

    Hello Cristiano,

    In daisy chain mode, were you able to use one serial port to get all ADC channels from all ADCs?

    Stephen

  • 0 in reply to stevenh
    Prodigy 30 points

    Hello Stephen,

         Sorry for delay in answer. Yes, I able to read all ADC channels in daisy chain. The only issue was time spent to read all channels (spi clock max 20MHZ, so in my case, 16 pulses * 12 channels / 20Mhz = 9,6us just to read).

         If this time is not a big deal for you, ok. Daisy chain works perfectly and using the gerbers sent to me I improve my pcb and finnally got realy good results.

    Cristiano 

  • 0 in reply to cristiano martins
    Guru 20025 points

    Hello Cristiano,

    Thanks for the reply.

    Do you mean you were able to read all channels from all ADCs using one SPI port (=SDO_A)?

    Stephen