SDAA378 August   2026 ADS125H18

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Detailed Description
    1. 2.1 Understanding ADS125H18 OWCS Operation
    2. 2.2 Using OWCS with Single-Ended Input Signals
      1. 2.2.1 Analyzing OWCS Behavior for Single-Ended Input Signals
      2. 2.2.2 Verifying OWCS Operation with a Single-Ended Input Using the ADS125H18EVM
        1. 2.2.2.1 Verifying OWCS Operation with a Single-Ended Input
        2. 2.2.2.2 Using a Fewer Number of Conversions for OWCS with a Single-Ended Input
          1. 2.2.2.2.1 Unsettled Data for Single-Ended Inputs
          2. 2.2.2.2.2 Settled Data for Single-Ended Inputs
        3. 2.2.2.3 How Input Capacitance Affects OWCS Performance for Single-Ended Inputs
        4. 2.2.2.4 Using the ADS125H18 Programmable Delay to Mitigate Settling Effects for Single-Ended Inputs
    3. 2.3 Using OWCS with Differential Input Signals
      1. 2.3.1 Analyzing OWCS Behavior for Differential Input Signals
      2. 2.3.2 Verifying OWCS Operation with a Differential Input Using the ADS125H18EVM
        1. 2.3.2.1 Verifying OWCS Operation with a Differential Input
        2. 2.3.2.2 Using a Fewer Number of Conversions for OWCS with a Differential Input
          1. 2.3.2.2.1 Unsettled Data for Differential Inputs
          2. 2.3.2.2.2 Settled Data for Differential Inputs
        3. 2.3.2.3 How Input Capacitance Affects OWCS Performance for Differential Inputs
          1. 2.3.2.3.1 Back-to-Back, Differential OWCS Measurements with Input Capacitance
        4. 2.3.2.4 Using the ADS125H18 Programmable Delay to Mitigate Settling Effects for Differential Inputs
    4. 2.4 Using the ADS125H18 Channel Sequencer to Implement an OWCS Algorithm
      1. 2.4.1 Example: Configuring the ADS125H18 Sequencer for the OWCS Algorithm
      2. 2.4.2 Understanding the OWCS Algorithm in the ADS125H18 Example Code
        1. 2.4.2.1 Initialization
          1. 2.4.2.1.1 Initialize the sequencer
          2. 2.4.2.1.2 Enter the "_step" Array Values
          3. 2.4.2.1.3 Analyze the Sequence
        2. 2.4.2.2 Starting the Sequencer and Processing Data
          1. 2.4.2.2.1 Update OWCS Step Values and Calculate "total_conversions"
          2. 2.4.2.2.2 Starting the Sequencer and Taking Data
          3. 2.4.2.2.3 Processing the OWCS Data
          4. 2.4.2.2.4 Using the OWCS Results
  6. 3Summary
  7. 4References
  8. 5Appendix A
    1. 5.1 Using OWCS with Redundant Systems
      1. 5.1.1 Dual, Redundant Systems versus Single-Device Systems
      2. 5.1.2 Using 1x OWCS versus 2x OWCS in a Dual Redundant System
      3. 5.1.3 Error Sources in Dual, Redundant Systems
        1. 5.1.3.1 RA1 and RB1 Errors
        2. 5.1.3.2 RA2 and RB2 Errors
        3. 5.1.3.3 VREF1 and VREF2 Errors
      4. 5.1.4 Measuring Differential Inputs in a Dual, Redundant System
      5. 5.1.5 Dual, Redundant System Summary

2.4.1 Example: Configuring the ADS125H18 Sequencer for the OWCS Algorithm

Figure 2-33 shows an example system that measures both input signals and monitoring signals as follows:

  • Five input channels in blue, including a combination of single-ended and differential voltage and current inputs
  • Three monitoring channels in red, including temperature, AVDD, and IOVDD

Moreover, Figure 2-33 highlights the ADS125H18 OWCS feature and associated multiplexer in green:

ADS125H18 Input Connections for the OWCS Algorithm ExampleFigure 2-33 ADS125H18 Input Connections for the OWCS Algorithm Example

Figure 2-34 uses the format shown in Figure 2-32 to demonstrate how to setup the sequencer for the example system in Figure 2-33. All information shown in Figure 2-34 can be stored in the ADS125H18 sequencer and was arbitrarily chosen for this example.

Example Sequencer Step for the OWCS AlgorithmFigure 2-34 Example Sequencer Step for the OWCS Algorithm

Interpret Figure 2-34 as follows:

  • Row 1 = the step number used for that step
  • Row 2 = the channel measured by that step
  • Row 3 = the number of conversions to measure on that step.
  • Row 4 = if the OWCS are enabled (on) or disabled (off) for that step

For example, Step 13 measures ten conversions between inputs AIN15 and RESN. Note that the ADS125H18 sequencer allows the user to configure many other parameters on a per-step basis; however these parameters are not necessarily relevant to the OWCS algorithm and are not discussed further in this document.

Figure 2-34 also shows that the "Channel" for the OWCS steps in green are to be determined, or TBD. These settings are initially TBD because they change from one sequence to the next. However, the input steps and monitoring steps remain unchanged. Figure 2-35 shows how to configure the OWCS steps during the first sequence: the first and second OWCS steps (#25 and #26, respectively) are both configured with AIN0-RESN because this is the same channel used in the first sequence step (#4). Important settings for the first sequence step are highlighted in yellow.

Example: Sequence 1 CharacteristicsFigure 2-35 Example: Sequence 1 Characteristics

Start the sequencer by setting the START bit or toggling the START pin. The ADS125H18 sequencer indexes through each step in Figure 2-35 from left to right and measures 129 total conversions. The user must decide how to use the information received from each input and monitoring step, as well calculate the OWCS threshold.

Reconfigure the OWCS steps before the next sequence starts if necessary. Figure 2-36 shows how to configure the OWCS steps during the second sequence: the first and second OWCS steps (#25 and #26, respectively) are both configured with AIN4-RESN while the third and fourth OWCS steps (#27 and #28, respectively) are both configured with AIN5-RESN. These settings are required because the second step (#7) measures a differential input but the OWCS feature must always measure single-ended channels. Important settings for the second sequence step are highlighted in yellow.

Example: Sequence 2 CharacteristicsFigure 2-36 Example: Sequence 2 Characteristics

Again, start the sequencer by setting the START bit or toggling the START pin. The ADS125H18 sequencer indexes through each step in Figure 2-36 from left to right and measures 153 total conversions because the last two OWCS steps are enabled in this sequence. The user must decide how to use the information received from the input and monitoring steps, as well as calculate the OWCS threshold for each single-ended input. Ideally, the calculated OWCS result for AIN4-RESN should be identical to the OWCS result for AIN5-RESN because this is a differential measurement.

Figure 2-37 follows the same logic to show how to reconfigure the OWCS channels before starting each of the next three sequences such that all input step channels in blue are analyzed for wire breaks. Important settings per sequence are highlighted in yellow.

Example: Sequences 3 through 5 Characteristics Figure 2-37 Example: Sequences 3 through 5 Characteristics

All input step channels have been diagnosed for wire breaks using the OWCS after sequence 5 completes. At this point, the user should reconfigure the OWCS channels to wrap back around to the first input step channel as shown in Figure 2-35, restarting the complete process. The user then decides how many total sequences to run as well as what to do if they detect a wire break.