Capsense 5th GEN - Any ideas on how to deal with the malfunction that occurs during immunity testing ?

[NXTY_Tatebayasi]

Hi, Community 

I would like to know how to deal with the possible malfunctions that occur in immunity tests on boards using capsense 5th generation.

I have found that in the community there is a discussion about the fourth generation, i.e. capsense by IDAC, regarding the baseline increase when temperature and humidity vary.

However, I have not been able to find any articles discussing the 5th generation, i.e., using cdac, and the measures to be taken in the immunity test, which is why I posted this.

If capsense exhibits the following behavior, how should it be addressed?

When the radio wave irradiation starts, the raw data drops significantly and the base line drops at the same time.
When the radio wave irradiation is stopped, the raw data returns to the value before the radio wave irradiation.

The range in which malfunctions occur in immunity testing is in the tens to hundreds of MHz range.

During the test, raw data from capsense is monitored via uart.

― Question ―

1. What can I do to prevent Raw counts from dropping? Please advise on both hardware and software methods.

2. If we were to take action in the capsense settings, would we be able to do so by changing the base value as in the previous generation of capsense?

3.  How long does it take to reset the lower baseline threshold?
4.  Also, can the reset time of the baseline be adjusted by the user?

Best Regards,

Chihiro Tatebayashi 

[Arpit_S · Accepted solution]

Hi @NXTY_Tatebayasi -San,

For EMC related issues in CapSense, you explore the opportunity to implement Ground Ring. For more information please refer to https://www.infineon.com/dgdl/Infineon-AN85951_PSoC_4_and_PSoC_6_MCU_CapSense_Design_Guide-Applicati... 7.5.3.1.2 Redirect and 7.4.12.3 Liquid tolerance with ground ring.

In case the RawCounts are getting decreased. I would recommend you to make use of Low Baseline reset Parameter and Negative Noise threshold.

Negative noise threshold
A threshold used to differentiate usual noise from the spurious signals appearing in negative direction. This
parameter is used in conjunction with the Low Baseline Reset parameter.
Baseline is updated to track the change in the Raw Count as long as the Raw Count stays within Negative Noise
Threshold, that is, the difference between Baseline and Raw count (Baseline – Raw count) is less than Negative
Noise Threshold.
Scenarios that may trigger such spurious signals in a negative direction include: a finger on the sensor on
power-up, removal of a metal object placed near the sensor, removing a liquid-tolerant CAPSENSE™-enabled
product from the water; and other sudden environmental changes.

Baseline is a low-pass-filtered version of raw counts, baseline is updated by low-pass filtering raw counts if the current raw count is within a range of (Baseline – Negative noise threshold) to (Baseline + Noise threshold). 

Keep Negative Noise threshold parameter less such that If the RawCounts continue to decrease and drop below Negative Noise Threshold then Low Baseline Reset will come into picture. This parameter is used along with the negative noise threshold parameter. It counts the number of abnormally low raw counts required to reset the baseline. It resets the baseline to the low raw count value when the number of low samples reaches the low baseline reset number.  Please refer to https://www.infineon.com/dgdl/Infineon-AN85951_PSoC_4_and_PSoC_6_MCU_CapSense_Design_Guide-Applicati... Section 5.3.2.3.7 Low baseline reset, 5.3.2.3 Selecting CAPSENSE™ software parameters 

Refer to Equation 34 Low baseline reset time as well for more information

Hope this helps!
Thanks!
Kind Regards

Arpit Srivastav