sx8635 Semtech Corporation, sx8635 Datasheet - Page 48

• Manufacturer Part Number: sx8635
• Description: Low Power, Capacitive Button And Wheel Touch Controller 12 Sensors With Enhanced Led Drivers And Proximity Sensing
• Manufacturer: Semtech Corporation

ADVANCED COMMUNICATIONS & SENSING
Please note that proximity sensors are configured as buttons and operate exactly the same way as touch buttons.
All the parameters and procedures described below apply similarly.
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_8, October 10
Button Parameters
Address
The SX8635 can report all touches of multiple fingers or the SX8635 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 SX8635 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.
Name
Bits
Table 18
Figure 49 T
Description
0x01: 1 second
…
0xFF: 255 seconds
(12 sensors) with Enhanced LED Drivers and Proximity Sensing
© 2010 Semtech Corp.
Button Configuration Parameters
Low Power, Capacitive Button and Wheel Touch Controller
ouch and Release Example
48
DATASHEET
www.semtech.com
SX8635