CapSense Performance Tuning with User Modules
CY8C20xx7/S CapSense
®
Design Guide
Doc. No. 001-78329 Rev. *E
41
4.3.3 Recommended C
MOD
Value for SmartSense_EMC_PLUS
The recommended C
MOD
value for a SmartSense_EMC_PLUS-based design is 2.2 nF. X7R or NPO type capacitors
are recommended for C
MOD
stability over temperature. The capacitor should have voltage rating not less than 5 V.
4.3.4 SmartSense_EMCPLUS User Module Parameters
Only four parameters must be set for this user module. These are:
Sensors Autoreset
Debounce
Modulator Capacitor Pin
Sensitivity Level
4.3.4.1 Sensors Autoreset
This parameter determines whether the baseline is updated at all times or only when the signal difference is below
the noise threshold. When set to Enabled, the baseline is updated constantly. This setting limits the maximum time
that a sensor may remain ON (typically it is 5 to 10 seconds), but it prevents the sensors from permanently turning
ON when the raw count suddenly rises without anything touching the sensor because of any failure condition of the
system.
4.3.4.2 Debounce
The Debounce
parameter adds a debounce counter to the sensor‟s active transition. For the sensor to be declared as
active from inactive state, a finger touch signal should be present on the sensor for debounce number of consecutive
scans. This parameter affects all of the sensors similarly.
4.3.4.3 Modulator Capacitor Pin
This parameter selects the pin to which the 2.2 nF/X7R/voltage rating more than 5 V C
MOD
capacitor is connected.
The available pins are P0[1] and P0[3].
Note
An external 2.2-nF capacitor is mandatory for SmartSense_EMCPLUS to work correctly.
4.3.4.4 Sensitivity Level
Sensitivity is used to increase or decrease strength of signal from a sensor. A lower value for sensitivity (0.1 pF)
leads to a stronger signal from the sensor. Designs with thicker overlays require stronger signals from sensors for
proper implementation. The available options for sensitivity selection are High (0.1 pF), Medium High (0.2 pF),
Medium Low (0.3 pF), and Low (0.4 pF).
To produce a stronger signal from a sensor (high sensitivity), the SmartSense_EMCPLUS UM must use more time
for sensor scanning. This means that setting 0.1-pF (High) sensitivity for a sensor will consume more scan time
compared to the sensor that has the sensitivity level set to 0.2 pF (Medium High).
Tuning best practice is to find the highest sensitivity value for the sensor to produce the required 5:1 SNR. You may
start the tuning with the highest sensitivity value (0.4 pF) and reduce the value as required to meet the 5:1 SNR
4.3.5 SmartSense_EMCPLUS User Module Specific Guidelines
All guidelines applicable to the SmartSense_EMC UM apply to the SmartSense_EMCPLUS UM. For general
guidelines about CapSense design and SmartSense_EMC_PLUS-based design, see the
design guide. This section documents a few important aspects of the SmartSense_EMCPLUS UM.
4.3.5.1 Sensor Scan Time, Response Time, and Memory Utilization
When a sensor is implemented using the SmartSense_EMCPLUS UM, the scan time of a sensor, response time of
the sensor, and RAM memory usage depends on the immunity mode selected in the user module.
With immunity mode Medium, sensor scan time is two times higher than a sensor with immunity mode Low. With
immunity mode High, the scan time of a sensor is three times higher than the scan time of a sensor with
immunity mode Low.
Increase in scan time proportionally increases the response time of a sensor. With immunity mode Medium,
response time is two times higher than that of a sensor with immunity mode Low. Similarly, response time of a
sensor with immunity mode High is three times higher than that of a sensor with immunity mode Low.
