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Single-key capacitive touch controllers for 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 portabledevice market. Applications extend beyond touch keys for single-button mechanical- switch replacement, to a range of body-proximitysensing scenarios. The chips have a power consumption of below 17 µA at 1.8V in low-power mode, and a fast wake-up time; from the lowpower state, when a key touch is detected, these devices will 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 (integrated circuits) automatically calibrate when powered up. The device will also stay calibrated, even with moisture build-up 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 sec it powers down, resets and self-calibrates to an assumed untouched state. The 1011 remains in the “touched” condition indefi nitely while it senses a contact; this allows uses such as detecting when an earpiece of a head set 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, as well as a confi gurable power-down timer, to shut down devices that users inadvertently left on.

The user can confi gure the key sensitivity on all devices for different panel thickness and materials. Electrodes can consist of any conductive material including transparent ITO (indium tin oxide). There are few constraints on key shape or size, allowing the user a great level of fl exibility 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. This functionality is typically present in toys to illuminate “hiddenuntil- lit” keys when a hand or a fi nger(s) approaches a consumer appliance. Packaging is a 2.9x1.6-mm SOT-23, and the chips need only two external components; pricing is from $0.20 in volume.

Atmel, www.atmel.com/products/touch.