ADS1115: ADS1115's safe time for switching between two channels

Chen,

The device should be able to switch between any channel immediately. The input multiplexer will shut off the first channel before engaging the next channel.

However, I would note that you should probably use the device in single-shot conversion mode and then wait for a specified amount of time to read the data and set the next channel and configuration. I think this is the easiest way to get the data you want out of the device for the expected channel. This in itself does add on a little delay between switching channels. I mentioned this just in case your customer is getting the wrong channel data for the ADC measurement. 

The issue of using the ADC in continuous conversion mode is knowing when a new configuration or new channel change takes place. For the ADS1115 in continuous conversion mode, a new configuration takes place after the conversion in progress completes. That means if you write a new configuration, this does not take effect immediately. This can lead to confusion over when the device receives the configuration, and when to collect data. Even if you use the ALERT/RDY pin to indicate the conversion completion, continuous conversion mode is usually more confusing to implement.

Using the device in single-shot conversion mode, you would:
1. Program the configuration register to make a conversion with the proper configuration.
2. Wait the data period + an extra 10% + 20us. This is the time it takes to make a conversion with 10% to account for variation in the internal clock and an extra 20us to wake up the device after the last conversion.
3. Read the last data.
4. Repeat from 1 to start the next channel.

As an example, with a data rate of 860SPS, this time period should be about 1.3ms for each conversion.

Joseph Wu