2. Overview of the AT42QT1010
2.1 Introduction
The AT42QT1010 is a digital burst mode charge-transfer sensor that is capable of detecting near-
proximity or touch, making it ideal for implementing touch controls.
With the proper electrode and circuit design, the self-contained digital IC will project a touch or proximity
field to several centimeters through any dielectric like glass, plastic, stone, ceramic, and even most kinds
of wood. It can also turn small metal-bearing objects into intrinsic sensors, making them responsive to
proximity or touch. This capability, coupled with its ability to self-calibrate, can lead to entirely new product
concepts.
The QT1010 is designed specifically for human interfaces like control panels, appliances, toys, lighting
controls, or anywhere a mechanical switch or button may be found. It includes all hardware and signal
processing functions necessary to provide stable sensing under a wide variety of changing conditions.
Only a single low-cost capacitor is required for operation.
2.2 Basic Operation
Figure 1-1 and Figure 1-2 show basic circuits.
The QT1010 employs bursts of charge-transfer cycles to acquire its signal. Burst mode permits power
consumption in the microamp range, dramatically reduces RF emissions, lowers susceptibility to EMI, and
yet permits excellent response time. Internally the signals are digitally processed to reject impulse noise,
using a “consensus” filter which requires four consecutive confirmations of a detection before the output
is activated.
The QT switches and charge measurement hardware functions are all internal to the QT1010.
2.3 Electrode Drive
For optimum noise immunity, the electrode should only be connected to SNSK.
In all cases, the rule Cs >> Cx must be observed for proper operation; a typical load capacitance (Cx)
ranges from 5–20 pF while Cs is usually about 2–50 nF.
Increasing amounts of Cx destroy gain; therefore, it is important to limit the amount of stray capacitance
on both SNS terminals. This can be done, for example, by minimizing trace lengths and widths, and
keeping these traces away from power or ground traces or copper pours.
The traces and any components associated with SNS and SNSK will become touch sensitive and should
be treated with caution to limit the touch area to the desired location.
A series resistor, Rs, should be placed in line with SNSK to the electrode to suppress ESD and EMC
effects.
2.4 Sensitivity
2.4.1 Introduction
The sensitivity on the QT1010 is a function of things like the value of Cs, electrode size and capacitance,
electrode shape and orientation, the composition and aspect of the object to be sensed, the thickness
AT42QT1010
© 2017 Microchip Technology Inc.
Datasheet
DS40001946A-page 8
