SX8644I05AWLTRT Semtech, SX8644I05AWLTRT Datasheet - Page 48

• Manufacturer Part Number: SX8644I05AWLTRT
• Description: 12-ch Capacitive Touch Solution (Button & Slider)
• Manufacturer: Semtech

ADVANCED COMMUNICATIONS & SENSING
A reliable button operation requires a coherent setting of the registers.
Figure 49 shows an example of a touch and a release. The ticks will vary slightly around the zero idle state.
When the touch occurs the ticks will rise sharply. At the release of the button the ticks will go down rapidly and
converge to the idle zero value.
As soon as the ticks become larger than the CAP thresholds (see registers of the previous section) plus the
hysteresis (defined in register BtnHysteresis) the debounce counter starts.
In the example of Figure 49 the touch is validated after 2 samples (BtnCfg [1:0] = 01).
The release is detected immediately (BtnCfg [3:2] = 00) at the first sample which is below the threshold minus the
hysteresis.
BtnCfg
BtnAvgThresh
Revision 7_3, January 10
Button Parameters
Address
The SX8644 can report all touches of multiple fingers or the SX8644 can be set to report only the first detected
touch. In the later case all succeeding touches are ignored. The very first touch should be released before a
next touch will be detected.
The user can select to have the interrupt signal on touching a button, releasing a button or both
In noisy environments it may be required to debounce the touch and release detection decision.
In case the debounce is enabled the SX8644 will count up to the number of debounce samples BtnCfg [1:0],
BtnCfg [3:2] before taking a touch or release decision. The sample period is identical to the scan period.
Small environmental and system noise cause the ticks to vary slowly around the zero idle mode value.
In case the ticks get slightly positive this is considered as normal operation. Very large positive tick values
indicate a valid touch. The averaging filter is disabled as soon as the average reaches the value defined by
Name
Bits
Table 18
Figure 49 T
Description
0x01: 1 second
…
0xFF: 255 seconds
Touch Controller (12 sensors) with Enhanced LED Drivers
© 2009 Semtech Corp.
Button Configuration Parameters
ouch and Release Example
48
Ultra Low Power, Capacitive Button and Slider
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SX8644