E102 Atmel, E102 Datasheet - Page 8

• Manufacturer Part Number: E102
• Description: KIT EVAL/DEV USING QT102-ISG
• Manufacturer: Atmel
• Series: Quantum, QTouch™r

Specifications of E102

• Sensor Type: Touch, Capacitive
• Sensing Range: 1 Button/Key
• Interface: Logic Level
• Voltage - Supply: 3V
• Embedded: No
• Utilized Ic / Part: QT102
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Sensitivity: -

3.4 Output Drive
The OUT pin is active high and can sink or source up to 2mA.
When a large value of Cs (>20nF) is used the OUT current
should be limited to <1mA 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.
3.5 Auto Off Delay
3.5.1 Introduction
In addition to toggling the output on/off with key touch, the
QT102 can automatically switch the output off after a specific
time. This feature can be used to save power in situations
where the switched device could be left on inadvertently.
The QT102 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 Sections 3.5.2, 3.5.3 and 3.5.4.
3.5.2 Auto Off - Predefined Delay
To configure the predefined delay the TIME pin is hard wired
to Vss, Vdd or OUT as shown in Tables 3.2 and 3.3. This
provides nominal values of 15 minutes, 60 minutes or infinity
(remains on until toggled off).
A single 1M 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
Figure 3.5 and Table 3.4). At the end of each acquisition
cycle the logic level of Vm is monitored to see if an Auto off
delay override is required (see Section 3.5.4).
Setting the delay multiplier to x24 will decrease the key
sensitivity. To compensate, it may be necessary to increase
the value of Cs.
lQ
•
•
•
three predefined delay times (Section 3.5.2)
the ability to set a user-programmed delay
(Section 3.5.3)
the ability to override the auto off delay (Section 3.5.4)
ELECTRODE
SENSE
Figure 3.5 Predefined Delay
Vm
RS
CS
Rm
3
4
SNSK
SNS
VDD
VDD
VSS
5
2
TIME
OUT
1
6
Vt
Rop
8
3.5.3 Auto Off - User-programmed Delay
If a user-programmed delay is required a resistor and capacitor
can be used to set the auto-off delay (see Table 3.5 and
Figure 3.6 The delay time is dependent on the RC time constant
(Rt x Ct) the output polarity and the supply voltage. Section 3.5.5
gives full details of how to configure the QT102 to have auto-off
delay times ranging from 1 minute to up to 24 hours.
K values (42 and 14.3) are obtained from Figures 3.10
and 3.11.
Note: Rt is in k , Ct is in nF.
3.5.4 Auto Off - Overriding the Auto Off Delay
In normal operation the QT102 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 Figures 3.7 and 3.8.
Output Type
Active high
Active low
OUT
OUT
Vdd
Vm
Vss
Vss
V
Vss
V
Vt
Vt
Table 3.5 Programmable Auto Off Delay
DD
DD
(Vm = Vss (delay multiplier = 1), V
ELECTRODE
Table 3.2 Predefined Auto-off Delay
Table 3.3 Predefined Auto-off Delay
Table 3.4 Auto-off Delay Multiplier
SENSE
Figure 3.6 Programmable Delay
Vm
RS
CS
Rm
Auto-off delay (t
Infinity (remain on until toggled to off)
15 minutes
60 minutes
Auto-off delay (t
15 minutes
Infinity (remain on until toggled to off)
60 minutes
Auto-off delay multiplier
t
t
Auto Off Delay (seconds)
(Rt x Ct x 15) / 42
(Rt x Ct x 15) / 14.3
o
o
3
4
(Active High Output)
(Active Low Output)
x 1
x 24
SNS
SNSK
VDD
VDD
VSS
5
2
TIME
OUT
o
o
)
)
QT102_2R3.05_1007
1
6
DD
Ct
Rt
= 3.5V)
Rop