SX8661I07AULTRT Semtech, SX8661I07AULTRT Datasheet - Page 57

• Manufacturer Part Number: SX8661I07AULTRT
• Description: IC, Capacitive Button Touch And Proximity Controller, 8 SENSOR, MLPQ-28
• Manufacturer: Semtech

Specifications of SX8661I07AULTRT

• Controller Type: Capacitive Touch Screen
• Ic Interface Type: I2C
• Supply Voltage Range: 2.7V To 3.6V
• Operating Temperature Range: -40°C To +85°C

ADVANCED COMMUNICATIONS & SENSING
BtnStuckAtTimeout
BtnStrongestHysteresis
BtnLongPressTimer
Revision v3.2, January 2011
A release is detected if the ticks are getting smaller as the value defined by:
The stuckat timer can avoid sticky buttons.
If the stuckat timer is set to one second then the touch of a finger will last only for one second and then a
compensation will be performed and button hence considered released, even if the finger remains on the
button for a longer time. After the actual finger release the button can be touched again and will be reported as
usual.
In case the stuckat timer is not required it can be set to zero.
This parameter defines the hysteresis value for the adjacent button filtering engine. This parameter is only
valid when BtnCfg has been configured to report the strongest touch.
When the SX8661 device has been configured to report the strongest touch, a situation may arise where the
CAP signals of two sensors are of approximately equal value. Environmental noise can cause the signals of
these two sensors to fluctuate as shown in Figure 55 (b).
As a result of that, the output of the SX8661 device would also change very quickly as each of the two sensors
becomes the sensor with the strongest touch value. To eliminate this jitter, the SX8661 device adds a
hysteresis element to the calculation of the strongest touch sensor. In that respect, the strongest CAP sensor
is calculated as the sensor whose value is greater that the second detected strongest CAP sensor by the
Strongest hysteresis amount.
For example, as shown in Figure 55, the strongest CAP sensor is initially CAP0 (Figure 55 (b)). CAP1
becomes the strongest detected touch only if at some point in time the following holds true:
Similarly, if CAP2 is now also touched, it will only become the strongest detected touch if:
CAP1 signal = CAP0 signal + StrongestHysteresis
CAP2 signal = CAP1 signal + StrongestHysteresis.
CapThreshold + CapThreshold * hysteresis.
CapThreshold - CapThreshold * hysteresis.
CAP0
CAP1
Strongest
Hysteresis
(a)
Figure 55
Low Power, Capacitive Button Touch and Proximity Controller
© 2011 Semtech Corp.
Strongest touch and Hysteresis
Fluctuation
57
(8 sensors) with LED Drivers and Analog Output
(b)
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SX8661