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ADS131A04: Ping pong between 2 ADCs

Todd Anderson3
Intellectual 370 points

Part Number: ADS131A04

All:

Sorry if I am showing my ADC ignorance, but I have a situation with 2 ADS131A04 parts, and I want to ping-pong between them.

I can calculate that I can "unload" a single ADS in roughly 8 usec at 25 MHz SPI, correct?

32 bits x 6 frames / 25 MHz = 7.68 usec.

So, question is - what is the fastest that a conversion can be done on the device?

Essentially, I would like to transfer ADS-A while ADS-B is converting, and then unload ADS-B while ADS-A is converting.

Regards,

Todd Anderson

  • 0
    TI__Guru 68326 points

    Hi Todd,

    Thanks for your post.

    Do you actually want the ADC conversions to be asynchronous between the two devices? Because, if not, it likely easier to synchronize the two devices, and use the entire data rate period (1 / fDATA) to read the data from both devices. You achieve this either by sharing the same SPI bus in a daisy-chain configuration, or by using one dedicated SPI peripheral on your MCU for each ADS131A04.

    The maximum data rate that can be achieved on a single SPI bus will depend on: 

    1. frame size
    2. max SCLK frequency (limited by IOVDD supply)

    The frame size is determined by the word size and number of words in each frame. If, for example, you decide to disable CRC or some of the ADC channels, you can use the Dynamic Frame mode to remove the unused words from the frame.

    The maximum data rate for the ADS131A04 is 128 kSPS. Using the maximum SCLK frequency of 25 MHz (IOVDD > 2.7 V), you can only read ~195 bits or 8 x 24-bit words. If you wish to use this data rate and word size, a parallel SPI bus will be your only option. By ping-ponging between two ADCs with a common SPI bus, you will only be reducing the time you have to read conversions before the results are overwritten with new data, which will further reduce the max data rate you can achieve.

    Regards,