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ADS1018: ADS1018

Alessandro Capponi
Prodigy 30 points

Part Number: ADS1018
Other Parts Discussed in Thread: ADS1118,

Hi

I use ADS1018 in continuos convertion mode and read two channels, I have finded in other post (specifically for ADS1118) that for read multichannels, when switch betweeen one channel to other I must discard firt acquisition and read second acquisition.

I work with 3300SPS and polling adc every 500usec, , so time convertion is 303 usec, I suppose that when change channel I can discharge only first convertion and read second, in this mode every 2ms I have correct values from channels, is it correct ? Or is best dicard more acquisitions ?

Maurizio

  • 0
    TI__Guru** 100885 points

    Maurizio,


    When using the multiplexer to change between channels, I generally recommend using the single-shot conversion mode. With continuous conversion mode it's hard to keep track of which channel has been enabled, and which channel you are receiving data for. Also data reads can be interrupted by a new conversion (output register holds the conversion until the next conversion completes - if a new data comes up during your read, the output will be corrupted).

    In single-shot mode you would:
    1. Set the configuration register, with data rate, PGA, and input channel with the start of the conversion.
    2. Wait the data period + 10% for internal oscillator variation + 20us (for wake up time) With a data rate of 3300SPS, this would be 353.3us.
    3. Read the data, and set the configuration register to start the next conversion (go back to 2.)

    If you wanted to use continuous conversion mode, you need to keep track of a few things. First, writing to the configuration register does not immediately change the channel that you've set the register to. This change occurs after the completion of the conversion that is in progress. If you don't keep track of when you set the conversion, this is why you may need to discard a conversion if you're switching channels. As mentioned earlier, you need to know when the conversion completes so that you can read out the data before the next conversion completes. In single-shot mode, there is no next conversion until you start it, so you can read out the data without problems.

    Again, if you're using multiple channels, I recommend using single-shot conversion mode.


    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 30 points

    Joseph Wu

    Thank you for quickly answer.

    I have chose continuos mode because from datasheet I have understood that in single mode I can request a convertion every (min. time between two convertion ) 7,8ms, because ads1018 after convertion enter in power down state.

    I need to have convertion as fast possible , can I work in single mode with a rate of 500usec (with 3300 SPS) ? This aspect is not clear into documentation.

  • 0 in reply to Alessandro Capponi
    TI__Guru** 100885 points
    Alessandro,


    Yes, you should be be able to run the ADS1018 in single shot conversion mode. With a minimum SCLK period of 250ns (which is about 4MHz) you should be able to quickly clock out the data and set up the next conversion.

    With the 32 bit data transmission, you should be able to do this in a minimum 8us (you'll probably need to add some time for a slower SCLK and timing for /CS). Regardless, this could take about 20us (for step 3 in the last post) and be added to the 353.3us that you wait for the conversion to complete.

    As I mentioned before, if try to use continuous conversion mode, you need to monitor the DOUT/DRDY line using it as an interrupt to see when the conversion completes and immediately read the data and set the next conversion before the next conversion completes. If you don't, you might get the wrong conversion data because the configuration was sent too late.

    Generally, I find it easier to start the conversion and wait a specific time period to read the data and send the configuration to start an new conversion


    Joseph Wu
  • 0 in reply to Joseph Wu
    Prodigy 30 points

    Joseph Wu

    Ok, thanks you

    Maurizio