AT42QT1012_10 Datasheet, PDF (17/28 Pages) ATMEL Corporation – One-channel Toggle-mode Touch Sensor IC with Power Management Functions

AT42QT1012
3.11.5
Auto Off – Overriding the Auto Off Delay
In normal operation the QT1012 output is turned off automatically after the auto-off delay. In
some applications it may be useful to extend the auto-off delay (“sustain” function) or to switch
the output off immediately (“cancel” function). This can be achieved by pulsing the voltage on
the delay multiplier resistor Rm as shown in Figure 3-11 and Figure 3-12 on page 18.
To ensure the pulse is detected it must be present for typical times as shown in Table 3-6.
Table 3-6. Time Delay Pulse
Pulse Duration
tp – series of short pulses, typically 65 ms
tp – long pulse, typically 250 ms
Action
“Sustain”/retrigger (reload auto-off delay counter)
“Cancel”/switch output to off state and inhibit further
touch detection until Vm returns to original state
While Vm is held in the override state the QT1012 inhibits bursts and waits for Vm to return to its
original state. When Vm returns to its original state the QT1012 performs a sensor recalibration
before continuing in its current output state.
Figure 3-11. Override Pulse (Delay Multiplier x1)
SENSE
ELECTRODE
VDD
RS
5
VDD
3 SNSK
CS
4 SNS
OUT ¹
Rm
VDD Vm
VSS
Tp
TIME ⁶
VSS
Rop
2
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