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TSC2004: Touch Panel Maximum Impedance

David Williamson
Prodigy 30 points
Part Number: TSC2004

Hi,

We are designing the TI part as a replacement for an obsolete Maxim part. We use a standard 4-wire resistive touch panel. Having been through the TSC2004 datasheet and all the application notes, we are left with one question. If the impedance range for normal resistive TPs is between 200Ohm and 2000Ohm on X and Y, what is the maximum X or Y impedance that will trigger a touch into the TSC2004, please? I have noted the comment on this forum about touch sensitivity being affected by the ease of the 2 ITO layers to be pressed.

many thanks for your help.

  • 0
    TI__Genius 16890 points

    Hi David,

    The TSC2004 can't do anything about the ease of pressing the two layers together.  When it is looking for a touch, for example see Figure 30 about Touch Detect, it is measuring a voltage.  Nothing will happen until enough force is put on the touch screen so that the two layers touch.  At that time in the example described in Touch Detect, the X+ input is brought to ground.  The resistance of the touch screen does not affect the trigger. 

    Also, when measuring position the TSC is only looking for a voltage.    A measurement of the Y position of the pointing device is made by connecting the X+ input to a data converter chip, turning on the Y+ and Y– drivers, and digitizing the voltage seen at the X+ input.  The voltage measured is determined by the voltage divider developed at the point of touch. For this measurement, the horizontal panel resistance in the X+ lead does not affect the conversion because of the high input impedance of the A/D converter.

    Mike

  • 0 in reply to Michael Stout
    Prodigy 30 points

    Hi Mike,

    Many thanks for your quick response. We have now re-looked at our understanding of the datasheet and moved forward, so that's a result thank you.