at42qt100a ATMEL Corporation, at42qt100a Datasheet - Page 7

• Manufacturer Part Number: at42qt100a
• Description: Qtouch? Charge Transfer Ic
• Manufacturer: ATMEL Corporation

3.2
3.3
9531A–AT42–02/09
Threshold
Max On-duration
Figure 3-3.
However, once Sync mode has been entered, if the SYNC signal consists of a series of short
pulses (>10 µs) then a burst will only occur on the falling edge of each pulse
Figure 3-4.
In Sync mode, the device will sleep after each measurement burst (just as in LP mode) but will
be awakened by the falling edge of the SYNC signal, resulting in a new measurement burst. If
Sync remains unchanged for a period longer than the LP mode sleep period (about 85 ms), the
device will resume operation in either Fast or LP mode depending on the level of the SYNC pin
(Figure
There is no detect integrator (DI) in Sync mode (each touch is a detection) but the Max
On-duration will depend on the time between SYNC pulses; see
Section 3.4 on page
with the SYNC period.
The internal signal threshold level is fixed at 13 counts of change with respect to the internal
reference level, which in turn adjusts itself slowly in accordance with the drift compensation
mechanism.
The QT100A employs a hysteresis dropout of two counts of the delta between the reference and
threshold levels.
If an object or material obstructs the sense pad the signal may rise enough to create a detection,
preventing further operation. To prevent this, the sensor includes a timer which monitors
detections. If a detection exceeds the timer setting the sensor performs a full recalibration. This
is known as the Max On-duration feature and is set to ~80s (at 3V). This will vary slightly with Cs
and if Sync mode is used. As the internal timebase for Max On-duration is determined by the
burst rate, the use of Sync can cause dramatic changes in this parameter depending on the
Sync pulse spacing.
3-3).
QT100A1
QT100A1
SNSK
SYNC
SNSK
SYNC
Sync Mode (Triggered by Negative Edges on SYNC)
Sync Mode (Short Pulses)
8. Recalibration timeout is a fixed number of measurements so will vary
SNSK
QT100A1
SYNC
sleep
sleep
sleep
sleep
>10us
slow mode sleep period
slow mode sleep period
>10us
sleep
sleep
>10us
Revert to Slow Mode
Revert to Fast Mode
Section 3.3 on page 7
AT42QT100A
(Figure
3-4).
and
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