AT42QT1012_10 ATMEL [ATMEL Corporation], AT42QT1012_10 Datasheet - Page 11

• Manufacturer Part Number: AT42QT1012_10
• Description: One-channel Toggle-mode Touch Sensor IC with Power Management Functions
• Manufacturer: ATMEL [ATMEL Corporation]

3.10
3.11
3.11.1
3.11.2
9543D–AT42–08/10
Output Drive
Auto Off Delay
Introduction
Auto Off – Predefined Delay
The OUT pin can sink or source up to 2 mA. When a large value of Cs (>20 nF) is used the OUT
current should be limited to <1 mA to prevent gain-shifting side effects, which happen when the
load current creates voltage drops on the die and bonding wires; these small shifts can
materially influence the signal level to cause detection instability.
In addition to toggling the output on/off with a key touch, the QT1012 can automatically switch
the output off after a time, typically ±10 percent of the nominal stated time. This feature can be
used to save power in situations where the switched device could be left on inadvertently.
The QT1012 has:
The TIME and SNS pins are used to configure the Auto Off delay and must always be connected
in one of the ways described in
To configure the predefined delay the TIME pin is hard wired to Vss, Vdd or OUT as shown in
Table 3-2 on page 12
minutes or infinity (remains on until toggled off).
A single 1 M resistor (Rm) is connected between the SNS pin and the logic level Vm to provide
three auto off functions: delay multiplication, delay override and delay retriggering. On power-up
the logic level at Vm is assessed and the delay multiplication factor is set to x1 or x24
accordingly (see
the end of each acquisition cycle the logic level of Vm is monitored to see if an Auto off delay
override is required (see
Setting the delay multiplier to x24 will decrease the key sensitivity. To compensate, it may be
necessary to increase the value of Cs.
• three predefined delay times
• the ability to set a user-programmed delay
• the ability to override the auto off delay
Figure 3-6 on page
and
Section 3.11.5 on page
Table 3-3 on page
Section
(Section
12,
3.11.2.
3.11.2)
Table 3-2 on page 12
(Section 3.11.5 on page
12. This provides nominal values of 15 minutes, 60
(Section 3.11.3 on page
17).
and
17)
Table 3-3 on page
12)
AT42QT1012
12). At
11