Datasheet

increasing signals. Increasing signals should not be compensated for quickly, since an approaching finger

could be compensated for partially or entirely before even approaching the sense electrode. However, an

obstruction over the sense pad, for which the sensor has already made full allowance, could suddenly be

removed leaving the sensor with an artificially elevated reference level and thus become insensitive to

touch. In this latter case, the sensor will compensate for the object's removal very quickly.

With large values of Cs and small values of Cx, drift compensation will appear to operate more slowly

than with the converse. Note that the positive and negative drift compensation rates are different.

3.7 Response Time

The QT1012 response time is highly dependent on the run mode and burst length, which in turn is

dependent on Cs and Cx. With increasing Cs, response time slows, while increasing levels of Cx reduce

response time.

3.8 Spread Spectrum

The QT1012 modulates its internal oscillator by ±7.5% during the measurement burst. This spreads the

generated noise over a wider band, reducing emission levels. This also reduces susceptibility since there

is no longer a single fundamental burst frequency.

3.9 Output Polarity Selection

The output (OUT pin) of the QT1012 can be configured to have an active high or active low output by

means of the output configuration resistor Rop. The resistor is connected between the output and either

Vss or Vdd (see Figure 3-4 and Table 3-1). A typical value for Rop is 100 kΩ.

Figure 3-4. Output Polarity (6-pin SOT23)

VDD

OUT

VSS

VDD

Rop

SNSK

Vop

SNS

SENSE

ELECTRODE

TIME

Cby

100 nF

AT42QT1012

Datasheet

DS40001948A-page 12