Cypress CapSense CY8C20x36 Uživatelská příručka stáhnout pdf (Strana 14)

14 Document No. 001-64846 Rev. *I Getting Started with CapSense

The CY8C20xx6A/AS/H family of CapSense controllers uses a single external component C

MOD

and a single

dedicated pin.

Figure 2-7. CY8C20xx6A/AS/H CSD Block Diagram

ISENSOR

Single

Slope ADC

Precharge

Clock

Cint(1.2nF)

High-Z

input

CY8C20x34/

CY8C20xx6A/AS/H

Gnd

= External Connection

AMUX

Vref

Rbus

Sw1

Sw2

iDAC

IDIFF

IDAC

2.3.4 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 an equilibrium voltage develops across the integration capacitor C

MOD

. This

equilibrium voltage is measured using a single slope ADC. When you place a finger on the sensor the capacitance

increases. Further, this causes the equilibrium voltage on C

MOD

to decrease and the ADC output increases that result

in an increase in the digital count.

The CSA_EMC method requires a single dedicated pin and a single external component, C

INT

, which is an integration

capacitor that is used by the single-slope ADC.

The CSA_EMC CapSense algorithm is developed 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 such as

inverters, transformers, and power supplies. For more detail on CSA_EMC CapSense, see Electromagnetic

Compatibility (EMC) Considerations.

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