AT42QT2120 Datasheet
Table Of Contents
- Features
- 1. Pinouts and Schematics
- 2. Overview
- 3. Wiring and Parts
- 4. I2C-compatible Communications (Comms Mode Only)
- 5. Setups
- 5.1 Introduction
- 5.2 Address 0: Chip ID
- 5.3 Address 1: Firmware Version
- 5.4 Address 2: Detection Status
- 5.5 Addresses 3 – 4: Key Status
- 5.6 Address 5: Slider Position
- 5.7 Address 6: Calibrate
- 5.8 Address 7: Reset
- 5.9 Address 8: Low Power (LP) Mode
- 5.10 Address 9 – 10: Toward Touch and Away from Touch Drift (TTD, ATD)
- 5.11 Address 11: Detection Integrator (DI)
- 5.12 Address 12: Touch Recal Delay (TRD)
- 5.13 Address 13: Drift Hold Time (DHT)
- 5.14 Address 14: Slider Options
- 5.15 Address 15: Charge Time
- 5.16 Address 16 – 27: Detect Threshold (DTHR)
- 5.17 Addresses 28 – 39: Key Control
- 5.18 Addresses 40 – 51: Pulse/Scale for Keys
- 5.19 Address 52 – 75: Key Signal
- 5.20 Address 76 – 99: Reference Data
- 6. Specifications
- Appendix A. I2C-compatible Operation
- Associated Documents
- Revision History
8
9634E–AT42–06/12
AT42QT2120
2. Overview
2.1 Introduction
The AT42QT2120 (QT2120) is a QTouchADC sensor driver. The device can sense from one to
12 keys, dependent on mode. Three of the keys can be used as sense channels for a slider or
wheel, leaving a maximum of nine standard touch keys. The device also supports the use of
proximity sensors and a guard channel.
The QT2120 includes all signal processing functions necessary to provide stable sensing under
a wide variety of changing conditions, and the outputs are fully debounced. Only a few external
parts are required for operation and no external Cs capacitors are required.
The QT2120 modulates its bursts in a spread-spectrum fashion in order to heavily suppress the
effects of external noise, and to suppress RF emissions. The QT2120 uses a QTouchADC
method of acquisition. This provides greater noise immunity and eliminates the need for external
sampling capacitors, allowing touch sensing using a single pin.
The QT2120 can operate in two ways; comms and standalone.
2.2 Modes
2.2.1 Comms Mode
The QT2120 can operate in comms mode where a host can communicate with the device via an
I
2
C bus. This allows the user to configure settings such as Threshold, Adjacent Key Suppression
(AKS), Detect Integrator, Low Power (LP) Mode, Guard Channel and Max Time On for keys.
2.2.2 Standalone Mode
The QT2120 can operate in a standalone mode where an I
2
C-compatible interface is not
required. To enter standalone mode, connect the Mode pin to Vdd before powering up the
QT2120.
In standalone mode, the start-up values are hard coded in firmware and cannot be changed.
The default start-up values are used. This means that key detection is reported via its respective
input/output.
The Guard channel feature is automatically implemented on key 1 in standalone mode. This
means that this channel has a higher sensitivity and is used to protect against false triggering,
perhaps by a hand covering all keys.
A proximity sensor is also available on channel (key) 0 in standalone mode.