Simple Capacitive Sensors serving Automotive TPMS Applications

FirstCall/ Atmel(R) Corporation recently announced the availability of the new highly-integrated and low-power ATA6285 and ATA6286 microcontroller-transmitter ICs with sensor interface for tire pressure monitoring (TPMS) sensor gauge systems. The new devices include all necessary building blocks to support the measurement and calibration of simple capacitive pressure and motion sensors plus the complete RF transmission functionality. These are the first such devices on the market.

The new ICs enable the development of cost-effective applications by allowing the system designer to freely choose simple, low-cost, non-calibrated sensors. These capacitive sensors can be calibrated very easily and with minimum effort by the customer’s firmware within the integrated AVR(R) microcontroller. As a result, the external sensors can be less sophisticated and smaller. This also makes the new ICs very well-suited for sensor manufacturers who wish to develop their own integrated sensor modules.

The single-package devices combine Atmel’s ATA5756 and ATA5757 RF transmitters with Atmel’s well-known, low-power, ATmega AVR 8-bit Flash microcontroller family. The new ICs are designed to control and transmit data gained from capacitive pressure and motion sensors. Their high functionality, such as integrated temperature sensor with shut-down mode, 90-kHz slow- oscillation mode for timer wake-up in sleep mode, and LF input with several header options, makes them an excellent fit for pressure sensor systems.

The new devices are optimized to ensure extremely low current consumption- in sleep mode it is as low as 0.5 microamps. The maximum sleep-mode current consumption is 0.85 microamps at 85 degrees C in 90-kHz slow-oscillation mode, whereas the current consumption during sensor measurement is as low as 200 microamps which is about 10 times less than piezo-resistive sensor solutions. In transmission mode, the typical current consumption is 8.5 mA at 6 dBm. The programmable, integrated 125-kHz wake-up receiver channel consumes less then 1.7 microamps in active listening mode.

The ATA6285 operates at 315 MHz, whereas the ATA6286 is used for 433 MHz operation. Both devices are suited for ASK and FSK transmission with a data rate of typically 10 kBaud in Manchester mode. The parts can be operated at 2V to 3.6V from a single Li-cell power supply at an operation temperature of -40 degrees C to +125 degrees C and a storage temperature of -40 degrees C to +150 degrees C.

Price and Availability

First samples in QFN32 packages are available now, high-volume production will start in mid 2007. Pricing for the ATA6285 and ATA6286 starts at US $2.60 each (at 50kpc quantities). To simplify and speed-up the design, Atmel provides a rich set of AVR standard tools (see http://www.atmel.com/dyn/products/tools.asp?family_id=607 ).

Footnotes:
ASK = Alternating Shift Keying
FSK = Frequency Shift Keying
LF = Low Frequency
LI = Lithium
TPMS = Tire Pressure Monitoring Systems