AK4160 Datasheet, PDF (11/40 Pages) Asahi Kasei Microsystems – 16-channel Capacitive Touch Sensor IC

[AK4160]
■ Correction of Environment Drifts
The Capacitance of a sense terminal is influenced from the hydrothermal condition and the grime of the surface.
The AK4160 monitors the measurement value continuously. If the value is changed by the environment, “The Noncontact
Reference Value” is corrected. The reference value is charged very slowly following the measurement value of not
touched status by the correction circuit. The threshold of touch detection and release detection is synchronized with the
reference value. In case of the touch detection, the reference value is not followed to the measurement value.
The increasing rate and the decreasing rate of the reference value can be configured independently. When a finger
approaches slowly to the touch switch, the measurement value is decreased gradually. The decreasing rate of the reference
value must be configured slower than the increasing rate to avoid false detection.
V
Touch
V
Environmental Drift
Reference Value
Release Threshould
Touch Threshould
Measurement Value
T
Reference Value
Measurement Value
Release Threshould
Touch Threshould
T
Figure 8. The Voltage of Sense Terminal and Automatic Correction of Environmental Drift
The initial reference value after the reset release can be selected from a user configuration and the automatic
configuration that configured to 32/32, 31/32, and 30/32 of the first measurement value. (Address 0x70 RIM1-0 bits)
■ Debounce
The touch status is updated when the output of the second filter is judged as touched or released for N times continuously
for a stabilized touch detection. The count “N” is user-selectable from 0 to 15 times. (Address 0x71 DEBT3-0, DEBR3-0
bits) The Update rate of the touch status is calculated as follows. “Sampling Rate of Second Filter x Sample Count of
Second Filter x Debounce Count”
■ Automatic Initial Setting
The capacitance of a sensor is different according to the size and the shape of a touch switch. The charge current and the
charge period should be configured adequately for optimal sensitivity to every touch switches. (Address 0x45-0x54
CCn5-0 bits, Address 0x55-0x5C CTn2-0 bits) The AK4160 has the automatic initial calibration that configured to the
optimal setting. (Address 0x5F ACC)
■ External Reset
The RSTN pin is input terminal for a low-active asynchronous reset with an internal pull-up resistor. A measurement
operation is aborted and the internal circuit is initialized immediately by the reset. The serial interface transaction is also
aborted. If the reset is executed in a transaction, an unintended access may occur. Therefore, the reset must be executed
without transaction of serial interface.
MS1313-E-01
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2011/11