AT42QT1011 View Datasheet(PDF) - Atmel Corporation

Part Name

Description

Manufacturer

AT42QT1011

Single-key QTouch® Touch Sensor IC

Atmel Corporation 

The QT1011 drift compensation is asymmetric; the reference level drift-compensates in one direction faster than it

does in the other. Specifically, it compensates faster for decreasing signals than for 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, usually in only a few seconds.

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 QT1011's response time is highly dependent on 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. The response

time will also be a lot slower in LP or SYNC mode due to a longer time between burst measurements.

3.8 Spread Spectrum

The QT1011 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 Features

3.9.1

Output

The output of the QT1011 is active-high upon detection. The output will remain active-high for the duration of the

detection.

3.9.2

HeartBeat Output

The QT1011 output has a HeartBeat “health” indicator superimposed on it in all modes. This operates by taking the

output pin into a three-state mode for 15 µs, once before every QT burst. This output state can be used to determine

that the sensor is operating properly, using one of several simple methods, or it can be ignored.

The HeartBeat indicator can be sampled by using a pull-up resistor on the OUT pin (Figure 3-6), and feeding the

resulting positive-going pulse into a counter, flip flop, one-shot, or other circuit. The pulses will only be visible when

the chip is not detecting a touch.

Figure 3-6. Obtaining HeartBeat Pulses with a Pull-up Resistor (SOT23-6)

VDD

5

HeartBeat" Pulse

Ro

VDD

1 OUT

SNSK 3

SNS 4

SYNC/MODE 6

VSS

2

AT42QT1010 [DATASHEET] 10

9542I–AT42–05/2013

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