Hello,
We have an issue with some resistive touch screens that are being controlled by the Texas Instrument ADS7843 component.
The touch screens being tested are faulty: the resistive values of the X axis on the right side got higher with time, resulting in a lower voltage output when touching in this area and, therefore, the cursor being drifted to the left:
Based on the application notes of the ADS7843, when in differential mode (which we are using), this problem should be automatically compensated:
Differential Mode
The operation of differential mode is similar to single-ended mode except that the internal FET switches will continue to be ON from the start of the acquisition period to the end of the conversion period. The voltage across the panel will also become the reference voltage to the A/D converter, providing a ratiometric operation. This means that if the voltage across the panel varies because of power supply changes, changes in the driver impedance with supply changes or temperature, or variations in the touch panel resistance with temperature these changes will be compensated for by the ratiometric operation of the A/D Converter.
Is my understanding correct, should the issue with the touch screen be compensated by the ADS7843?
If so, why are we still seeing the issue in our application when we use the ADS7843 in differential mode?
Thank you in advance for your support.
