Datasheet

CY8C20xx6A/H CapSense Design Guide Doc. No. 001-65973 Rev. *A 11
2.2.3 CapSense Successive Approximation Electromagnetic Compatible (CSA_EMC)
Cypress’s CSA_EMC method also uses a switched-capacitor circuit on the front end of the system to convert the
sensor capacitance to an equivalent resistor. An internal constant current source called the iDAC is calibrated with a
successive approximation procedure until a preset voltage develops across the equivalent resistor. This baseline
voltage is measured using a single-slope ADC. When a finger is on the sensor, the capacitance increases and the
equivalent resistance decreases. This causes the voltage across the resistor to decrease and the ADC output to
increase. This results in an increase in the digital count.
The CSA_EMC method requires one external component, C
MOD
Figure 2-6. Block Diagram of CSA_EMC
. This is an Integration capacitor that is used by the
single-slope ADC.
Figure 2-7. CSA_EMC Equivalent Circuit
The CSA_EMC CapSense algorithm has been enhanced to work well in the presence of RF interference. CSA_EMC
is used in applications where CapSense is exposed to conducted interference, AC noise, and other noise sources
that include inverters, transformers, and power supplies. CSA_EMC User Module Low-Level Parameters discusses
this topic in detail.
For an in-depth discussion of Cypress’s CSA_EMC sensing method, refer to PSoC® CY8C20x66, CY8C20x66A,
CY8C20x46/96, CY8C20x46A/96A, CY8C20x36, CY8C20x36A Technical Reference Manual (TRM)