Cypress CE66058 Manual - Página 11

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Appendix: CSD Calibration

For optimum performance, the CSD parameters are tuned with the actual CapSense hardware and overlay.

the steps necessary to calibrate the CSD.

Start with the default settings of the CSD User Module.

Using the CY3240-I2USB Bridge/UART with the actual hardware and overlay, capture the raw counts, baseline, and

difference counts for the sensors.

Coarse tuning: Check if the signal-to-noise ratio (SNR) is greater than 5. If the SNR is less than 5, increase the SNR using

the recommended PCB guidelines, increasing the resolution of the CSD and reducing the scan speed of the CSD. For

more information about the PCB guidelines, refer to the Getting Started with CapSense Design Guide.

Fine tuning: Check if the SNR is greater than 8. If it is less than 8, reduce the Ref Value parameter to increase the SNR.

Check if the total scan time for all the sensors meets the requirement. If it does not, reduce the resolution and/or increase

the scan speed. As these parameters also affect the SNR, go back to step 3. With a couple of passes, arrive at the

optimum resolution and scan the speed parameters that produce the best SNR and the desired scan time.

Capture the difference counts when the button is activated. Set the finger threshold parameter to 75 percent of the peak

value.

Set the noise threshold to 40 percent of the peak value.

Set the negative noise threshold to half of the noise threshold.

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Figure 11. CSD Calibration Flowchart

Document No. 001-66058 Rev.*E

Dynamically Switch CSD Bleed Resistor

Figure 11

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