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R and C values on CapSense lines for EMC

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R and C values on CapSense lines for EMC


Question: How effective it is to increase R and C values on CapSense lines for EMC?
Response: During EMI testing, EM radiation will be created using particular test set up specified in related standard. To avoid or filter this radiation getting affected to CapSense circuitry, low pass filter can be created on CapSense Lines. This low pass filter will be a combination of series resistor and pin (I/O) capacitance.

Normal recommended value is 560ohm resistor on CapSense lines.
Consider following conditions:

1. Addition of  Capacitor with 560 ohm on CapSense line.
A1: Addition of Capacitor will increase parasitic capacitance of pad and so it is not recommended.

2. Inserting  higher value resistor more than 560ohms.
A2: Increasing resistor value will decrease low pass filter cut off frequency, but it will also increase response time of CapSense. So it is a trade of between low pass filter cut off frequency and response time.

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‎Jun 26, 2009 08:04 AM
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