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[FAQ] How to set and optimize baseline tracking for temperature variations in a button application using LDC2112, LDC2114 or LDC3114?

Other Parts Discussed in Thread: LDC2114, LDC2112, LDC3114

The basics of baseline tracking using the LDC2112, LDC2114, and LDC3114 are described in the LDC211x and LDC3114 Internal Algorithm Functionality app note but this FAQ will discuss how to use this feature for dealing with temperature variations. 

  • Baseline tracking allows an inductive sensing device to compensate for temperature variation in its environment. As temperature increases or decreases, the sensed inductance will change as well and can impact the data read from the device. In button applications, the threshold for a button press can be falsely triggered by temperature change to the system if not handled properly. Even if baseline tracking is implemented, a temperature shift fast enough could still cause a button press if the tracking isn't keeping up with the change. With this in mind, it is important to consider the fastest temperature change and max temperature change that will be occurring to the device. If the baseline tracking is not fast enough to keep up with the temperature change a false button press can be detected by the device. The image below shows this scenario.

     

     

    Adjusting the baseline to be faster can reduce the chance of having a false button press due to rapid temperature change. Our LDC2112, LDC2114, and LDC3114 devices have a baseline increment setting included in their baseline tracking features so this can be tuned. The down side to using the baseline tracking like this is that during a normal button press, the baseline tracking can cause the button to de-assert as shown below.

     

     

    This issue can be solved by adding a pause to the baseline tracking. The LDC2112, LDC2114, and LDC3114 have a BTPAUSE setting that does this function included in their registers.

     

      

    For systems that operating in an environment with a rapid temperature change, it can be very beneficial to use a combination of a faster baseline tracking along with the tracking pause. One concern with this implementation is when the pause occurs during a fast temperature change. Under the right conditions, this could create a stuck button scenario. This can be handled with software if monitored properly, but could also be avoided by disabling the BTPAUSE setting.

     

    The needs of every application is different so it is important to understand the environment of the application and test the button to find the best implementation of the baseline tracking settings.