Making proximity based sensor EMI, EMC & ESD proof.

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create_sys
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Hello,

We have successfully prototyped human detection sensor to be used in Class II medical devices. The system is comprising of 4 small individual PCBs packaged into a plastic enclosure that will approach the human body. Every PCB has one PSOC 4. Although it's very well packaged we want to understand the below facts.

1. The device will undergo ESD tests in which the ESD generator will try to pass 15KV air discharge & 8KV contact dischange. In this case, will the proximity sensor PCB ( which is directly connected to PSoC 4 MCU pin ) will sustain the 8KV/ 15KV ESD voltage?  

2. We can connect the ESD diode to suppress the ESD in between the MCU pin ( acting as proximity sensor ) & gnd. In this case, will the performance of proximity will get affected? What are general rules that we can follow to make sure our compliance testing will get passed?

3. We are going to conformally coat the PCB from both sides. Despite this, any change in humidity will affect the sensor performance. Or How to make sensor immune to change in humidity?

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

Hi @create_sys 

 

1. This depends on the thickness of the plastic enclosure that is being used in the design. You can take a look at this table that lists the minimum thickness that is required to prevent a 12kV discharge - 

Hari_0-1630064301337.png

 

 

2. Yes, an ESD diode will be required. However, this will affect the proximity sensor as the ESD diodes will increase the parasitic capacitance of the sensor. An increase in parasitic capacitance reduces the signal level that you will observe on the sensors. It is still recommended as we can increase the resolution or apply other firmware techniques (such as firmware filters) for increasing the proximity sensing distance. 

 

3. Changes in humidity and temperature will affect the sensor. This is unavoidable as the physical capacitance changes with humidity. However, the baseline will track such changes and this will not contribute to any false detections. 

 

You can take a look at the ESD Protection section from our AN - CapSense Design Guide - https://www.cypress.com/file/46081/download#page=142

 

Best regards, 
Hari

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

Hi @create_sys 

 

1. This depends on the thickness of the plastic enclosure that is being used in the design. You can take a look at this table that lists the minimum thickness that is required to prevent a 12kV discharge - 

Hari_0-1630064301337.png

 

 

2. Yes, an ESD diode will be required. However, this will affect the proximity sensor as the ESD diodes will increase the parasitic capacitance of the sensor. An increase in parasitic capacitance reduces the signal level that you will observe on the sensors. It is still recommended as we can increase the resolution or apply other firmware techniques (such as firmware filters) for increasing the proximity sensing distance. 

 

3. Changes in humidity and temperature will affect the sensor. This is unavoidable as the physical capacitance changes with humidity. However, the baseline will track such changes and this will not contribute to any false detections. 

 

You can take a look at the ESD Protection section from our AN - CapSense Design Guide - https://www.cypress.com/file/46081/download#page=142

 

Best regards, 
Hari

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