• State
  • Locked Locked
  • Replies 7 replies
  • Subscribers 45 subscribers
  • Views 815 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

ADS131A04: ADS131A04 adaptive sampling and synchronization

Pierre De Vos
Prodigy 10 points
Part Number: ADS131A04
Other Parts Discussed in Thread: ADS131M04, AMC131M03

Hi,

We have an energy measurement instrument that measures three phase voltage and current.  We are using three discrete single channel SAR ADCs each for voltage and current, six in total.  The three voltage ADCs are daisy chained together and so are the current ADCs.  The two groups of ADCs are each isolated from the host by two sets of digital isolators.

Both groups are connected to a FPGA that controls the sample rate and the serial bit streams coming from the ADCs.  It is important that all voltage and current channels are sampled simultaneously.

In some cases we use Rogowski coils to measure the current.  Because the output signal of these are so small it is quite a challenge to get high accuracy.  I have recently seen mentioned ADS131A04.  In the datasheet it mentions direct connection to Rogowski coils.  Also the dynamic range is good, 10000:1.  I would like to try these in my application to try improve the accuracy, but I need to clarify some questions.

Can I keep the existing voltage SAR ADCs and synchronise the ADS131A04 to them or would I have to use an ADS131A04 for the voltage channels as well?

Can I control the sample rate by controlling the clock input from the FPGA?

Regards

Pierre

  • 0
    TI__Mastermind 46005 points

    Hi Pierre,

    SAR ADC operation is quite different from Delta-Sigma ADC. In SAR ADC, it's simple to control the sampling rate of the ADC or achieve simultaneous sampling by using a conversion start signal which is usually a dedicated pin on most SAR ADCs. Delta-Sigma ADCs operate differently and they keep converting and running continuously, so they usually do not have a dedicated conversion start pin, however some of Delta-Sigma ADCs have a SYNC pin to synchronize with external event or other devices.

    ADS131A04 supports three interface mode, you can configure the ADC in either synchronous master or synchronous master mode for collecting data from all ADC devices. The master can be a device used in asynchronous interrupt mode, a device used in synchronous mater mode or a microcontroller/FPGA, and also the master must have a synchronous clock for all ADC devices so that all ADC devices work at exactly same timing to maintain synchronization. Please see more details in the section 9.5.2.2 and 9.5.2.3 in the datasheet. 

    In ADS131A04, the output data rate is determined by the oversampling ratio (OSR) and the modulator frequency which is different from SAR ADCs. Please see the table 30 for the data rate based on the OSR setting and the modulator frequency (fMOD).  Please notice that the fMOD is determined by two configurable clock dividers: 

    • ICLK = CLKIN / CLK_DIV[2:0]
    • MODCLK = ICLK / ICLK_DIV[2:0]

    Based on these information, I would recommend you to use same type ADCs for synchronization. 

    Best regards,

    Dale

  • 0 in reply to Dale Li
    Prodigy 10 points

    Hi Dale,

    Thanks for the answer. I will look into this. Only thing is If I use two ADS131A04s, I will not be able to daisy chain them directly as both will have their own isolation barrier in the SPI side.  Any ideas on this?

    Also I see there is a ADS131M04.  Is the main difference the PGAs on the M04?

  • 0 in reply to Pierre De Vos
    TI__Mastermind 46005 points

    Hi Pierre,

    In synchronous slave mode on ADS131A04, the /DRDY can be used as a fourth input signal as a synchronization to align new data ready with an external event or with a second ADS131A0x device. Please see 9.5.2.3 section in the datasheet.

    The following table shows key difference between A04 and M04 ADC:

    Are you considering to use a single ADC with integrated DC/DC converter and digital isolation? for example, 3-ch, Simultaneous-Sampling, 24-Bit,  Isolated Delta-Sigma ADC With Integrated DC/DC Converter, a /SYNC conversion synchronization input can be easily used to synchronize two ADCs.

    Best regards,

    Dale

  • 0 in reply to Dale Li
    Prodigy 10 points

    Hi Dale,

    I think the M04 might be more suitable for Rogowski coils?

    For the isolated ADC, which part do you have in mind?

    Regards

    Pierre

  • 0 in reply to Pierre De Vos
    TI__Mastermind 46005 points

    Hi Pierre,

    Yes, M04 can be used for Rogowski coils.

    The part with integrated isolation is not released yet. It's AMC131M03. If you are interested in it, we can have more communication offline and it may need a NDA to share the details.

    Best regards,

    Dale

  • 0 in reply to Dale Li
    Prodigy 10 points

    Hi Dale,

    Do you have an idea when they will be released?  I have some time constraints so maybe I should first focus on what's available now.

  • 0 in reply to Pierre De Vos
    TI__Mastermind 46005 points

    Hi Pierre,

    It will be later this year. You can look into M04 first and no problem. 

    Thanks&regards,

    Dale