Single-key capacitive touch controllers target use in portable products

Atmel has incorporated the technology of its QTouch charge-transfer capacitive touch sensors into a series of single-key touch controllers for the portable-device market. Applications extend beyond touch keys for single-button mechanical-switch replacements to a range of body-proximity-sensing scenarios. The chips have a power consumption of less than 17 µA at 1.8V in low-power mode and a fast wake-up time. From the low-power state, when these devices detect a key touch, they temporarily switch to a 12.6-msec fast-response mode, allowing rapid detection of additional touches.

As with other related parts, the AT42QT101X family uses spread-spectrum modulation to ensure good EMC (electromagnetic compatibility). The ICs automatically calibrate when you power them up and remain calibrated, even with moisture buildup or other contaminants on the touch surface.

The family comprises the AT42QT1010, AT42QT1011, and AT42QT1012. The 1010 part includes a timer to reset a “stuck-key” condition: After 60 seconds, it powers down, resets, and self-calibrates to an assumed untouched state. The 1011 remains in the “touched” condition indefinitely when it senses a contact; this feature allows uses such as detecting when an earpiece of a headset is in the user’s ear canal or detection of face proximity in a smartphone. The 1012 includes a touch-on/touch-off, or toggle, key and a configurable power-down timer to shut down devices that users inadvertently leave on.

Users can configure the key sensitivity on all devices for different panel thickness and materials. Electrodes can consist of any conductive material, including transparent indium-tin oxide. There are few constraints on key shape or size, allowing the user a great level of flexibility in the industrial design. The user can also set up the IC for use as a proximity sensor, allowing detection of a nearby hand or object. Toys typically have this function to illuminate “hidden-until-lit” keys when a hand or a finger approaches a consumer appliance. The devices come in a 2.9×1.6-mm SOT-23 package and need only two external components. Prices start at 20 cents (volume quantities).

Atmel