Data Sheet

interference, or it can be used to enhance noise immunity from low frequency sources such as 50Hz or

60Hz mains signals.

The SYNC pin is sampled at the end of each burst. If the device is in Fast mode and the SYNC pin is

sampled high, then the device continues to operate in Fast mode (Figure 3-1). If SYNC is sampled low,

then the device goes to sleep. From then on, it will operate in SYNC mode (Figure 3-2). Therefore, to

guarantee entry into SYNC mode, the low period of the SYNC signal should be longer than the burst

length (Figure 3-3).

Figure 3-3. SYNC Mode (Triggered by SYNC Edges)

SYNC

SNSK

slow mode sleep period

sleep

sleepsleep

Revert to Fast Mode

Revert to Slow Mode

slow mode sleep period

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) instead of on each

change of SYNC signal, as normal (Figure 3-3).

In SYNC mode, the device will sleep after each measurement burst (just as in LP mode) but will be

awakened by a change in the SYNC signal in either direction, resulting in a new measurement burst. If

SYNC remains unchanged for a period longer than the LP mode sleep period (about 80 ms), the device

will resume operation in either Fast or LP mode depending on the level of the SYNC pin (Figure 3-3).

There is no Detect Integrator (DI) in SYNC mode (each touch is a detection),, refer toSection 3.4.

Recalibration timeout is a fixed number of measurements so it will vary with the SYNC period.

Figure 3-4. SYNC Mode (Short Pulses)

SNSK

SYNC

>10 sμ >10 sμ >10 sμ

3.2 Threshold

The internal signal threshold level is fixed at 10 counts of change with respect to the internal reference

level, which in turn adjusts itself slowly in accordance with the drift compensation mechanism.

The QT1011 employs a hysteresis dropout of two counts of the delta between the reference and

threshold levels.

AT42QT1011

Datasheet

DS40001947A-page 11