4.1.10 Active Mode Scan Type

The active mode scan type, which is stored in the configuration profile, controls whether the capacitive sensing engine in active mode

will scan only once during the active mode scan period before going to sleep, or whether the engine will continue scanning as quickly

as possible during the active mode scan period, never entering a low power state.

For optimal responsiveness, the engine should be configured to run with free run mode enabled. Setting the scan mode to 'free run'

causes touch qualification on a new touch to occur as quickly as the scanning engine can convert and process samples on all sensors.

In this mode, qualification time is not bounded by active mode scan period, and is only bounded by scanning configuration factors such

as the debounce setting, the number of enabled sensors, the accumulation setting on each sensor, and the timing constraints of any

enabled component.

For optimal current draw when in active mode, the engine should be configured to use the 'one scan per period' mode setting. In this

case, touch qualification is bound by the scan period and the debounce setting of the device.

Touch Event

(t = 0 ms)

10 ms

20 ms

30 ms

40 ms

Optimized

Active

sample

sample

Active

process

additional

processing

process

additional

processing

Sleep

sleep

sleep

debounce

count = 1

touch

qualified

Figure 4.2. Timing and Current — One Sample Per Period Mode

Touch Event

(t = 0 ms)

10 ms

20 ms

30 ms

40 ms

Optimized

Active

sample

Active

process

additional

processing

Sleep

debounce

count = 1

touch

qualified

sample

process

additional

processing

Figure 4.3. Timing and Current — Free Run Mode

4.1.11 Sleep Mode Scan Period

The sleep mode scan period defines the rate at which a scan of the inputs enabled as wake-up sources are sampled. Each enabled

sensor can also be enabled as a wake-up source. After the sleep mode scan completes, the scan is processed for a qualified candidate

touch. If a candidate touch is qualified, the system wakes form sleep mode and enters active mode scanning.

The sleep mode scan period is stored in the configuration profile and is defined in units of ms.

CPT112S Data Sheet

Functional Description

silabs.com | Smart. Connected. Energy-friendly.

Preliminary Rev. 0.1 | 15