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PSoC™ 4

taas_3144281
Level 5
50 replies posted 25 replies posted 10 likes received
Level 5

Hi.

This is an additional question for the discussion "https://community.cypress.com/t5/PSoC-4-MCU/CapSense-Liquid-Tolerance-Layout/m-p/54042#M4665".

My customer use CapSense.

My customer wants a liquid tolerance layout in one layer.

So I thought about the layout as shown below.

taas_3144281_0-1613468643210.png

This is created on the FPC board.

The guard sensor will be cut off in order to realize it with one layer.

I understand that touching Sensor traces will falsely detect it.

The Guard sensor shorts on the board.

The guard sensor is then designed to enclose the button.

Is the function of the guard sensor maintained even in this case?

Best Regards.

 

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Hari
Moderator
Moderator 750 replies posted 500 replies posted 250 solutions authored
Moderator

Hi @taas_3144281,

 

The layout shared in the previous thread is preferable over this one due to the following reasons:

1. The 3 guard sensor traces will run through the entire flex PCB and can only join at the connector. This will increase the Cp of the guard sensor considerably and might lead to noise due to incorrect charging and discharging. 

2. You can see that there are 3 shield islands in this design

Hari_0-1613474051003.png

 

This will cause improper shield operation as well due to the long path of the shield. 

3. Since the guard sensors need to be routed till the connector, this will also lead to an increase in the number of pins in the connector required to route the guard sensors (3 additional pins). 

 

In the previous design as well, I would recommend placing a thick trace to connect the shield hatch inside to the one outside.

Hari_1-1613474513497.png

 

Best regards, 
Hari

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