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MSP430FR2533: Air gap and liquid torelant touch

U-SK
Genius 5840 points
Part Number: MSP430FR2533

Hello,

My customer is considering to use MSP430FR2533 with liquid tolerant touch.

But they are plan to develop the board with 6mm air gap and 1.5mm acrylic overlay.

And they want to pass IEC61000-4-3 test.

We recommended bridge material between acrylic and electrode, but they don't want to use it in terms of cost.

Do you think above can be achieved?

Or, is bridge materials mandatory? 

The number of buttons is 10, and the size of biggest button is 4.5 cm2.

Regards,

U-SK

  • 0
    TI__Genius 12615 points

    Hi U-SK,

    In general, yes, you want to have some bridging material material between the electrodes and acrylic for two reasons. First, with an air gap (dielectric ~ 1, the e-field will be weaker at the point of where the water level is vs bridging plastic (dielectric ~3). This means Captivate will have to operate with higher sensitivity, making it more susceptible to noise and possibly not passing the IEC 61000-3 conducted noise tests. The second reason is, with an air gap, the dielectric properties can change due to changes in temperature and humidity. This makes it difficult to maintain the calibration.

    BR,

    Leo

  • 0 in reply to Leonardo Estevez
    TI__Guru 60181 points

    Hi U-SK,

    I understand the customer does not want the expense of a "bridging" material.  The bridging material does not need fill completely over the PCB, just over the buttons.  The material can be metal (spring), plastic or even a compressible conductive silicone or foam (prefer silicone because foam has many air pockets).

    This is described in the Captivate Technology Guide, design guide section.

    Here is screen shot, but refer to the link above.

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