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ADS1115: ADS1115 in continuous mode with alternating channels

Aliaksei Belakurski
Prodigy 20 points
Part Number: ADS1115


Hi,

Can I use ADS1115 in continuous mode while alternating input channels on each read. If programmed, does the input channel change starts in the beginning of next conversion, or immediately, (I could not find answer to this question in the datasheet)?

If I setup the chip to provide interrupt on RDY pin, and in the ISR program the config for the next conversion, and read the analog value for the same channel. Will this work or do I have to use single shot mode if I need to alternate input channels? My concern is jitter in sampling timing if conversion is started by software.

Thanks,

-Aliaksei.

 

  • 0
    TI__Intellectual 1610 points

    Hello Aliaksei,


    Thank you for your query.

    If the device is in continuous-conversion mode, the change in the MUX occurs after the current conversion is completed, and does not change immediately after changing the register. You can use the RDY pin to provide an interrupt, but in continuous conversion mode, you will have to discard the first sample and use the second sample since the first sample might have the previous channel data. For this reason, to maximize the throughput and minimize the conversion time while multiplexing between channels, it is highly recommended to run the device in single-shot mode.

    For further explanation on the conversion times and procedure for channel multiplexing in single-shot and continuous conversion mode, we would like you to refer to the below threads:

    https://e2e.ti.com/support/data_converters/precision_data_converters/f/73/p/526236/1916483#1916483

    https://e2e.ti.com/support/applications/automotive/f/26/p/552044/2018149#2018149

    https://e2e.ti.com/support/data_converters/precision_data_converters/f/73/p/552080/2017119#2017119

    Please let me know if you have any further questions.

    Thanks,

    Krunal

  • 0 in reply to Krunal Maniar
    Prodigy 20 points
    Hi Krunal,

    Thanks for super quick reply.
    I have 2 questions:
    1. what is "data rate variability" exactly: is it clock accuracy across different chips, or is it clock run time stability on a particular chip?
    2. what is relationship between ready output and S1 and S2 signals (on figure 23 in the datasheet) in continuous operation mode, I'm ok with reading previous channel data in ISR, as long as it is always previous channel data, and I don't care about the very first sample, and I'm going to switch channels on every sample. Is it guaranteed that new conversion is started (S1 front edge )at the moment of ready output active edge? Datasheet suggests that in continuous mode new conversion is started immediately after completing the old one. Are you saying that there is no way to guarantee this, and one shot is the only mode of operation when you switch channels on every sample?

    Thanks,
    -Aliaksei.
  • 0 in reply to Aliaksei Belakurski
    TI__Intellectual 1610 points

    Aliaksei,

    Please check my reply below:

    1. what is "data rate variability" exactly: is it clock accuracy across different chips, or is it clock run time stability on a particular chip?

    It is the clock accuracy across different chips. The internal oscillator frequency and hence the data rate across different chips could vary by ±10%.


    2. what is relationship between ready output and S1 and S2 signals (on figure 23 in the datasheet) in continuous operation mode, I'm ok with reading previous channel data in ISR, as long as it is always previous channel data, and I don't care about the very first sample, and I'm going to switch channels on every sample. Is it guaranteed that new conversion is started (S1 front edge )at the moment of ready output active edge? Datasheet suggests that in continuous mode new conversion is started immediately after completing the old one. Are you saying that there is no way to guarantee this, and one shot is the only mode of operation when you switch channels on every sample?

    If you want to switch channels on every sample, single-shot mode is the only option.

    In continuous-conversion mode, the first sample data can be either from the previous channel or the new channel; it depends precisely on when the command is sent to update the register setting in the middle of conversion. For this reason, I would not always assume that the first sample is either from the previous channel or from the new channel. The second sample will always have the data for the new channel though.

    In single-shot mode, the user initiates the start of conversion by writing a '1' to the OS bit of the Config Register and has a better control on when to start a conversion, change the channel setting, etc. For this reason, we highly recommend single-shot operation for channel multiplexing with optimum throughput and performance.

    Thanks,

    Krunal