Atmel Automotive Solutions for Car Access Applications

A driver can touch the car door and it will unlock the vehicle (passive entry). Pressing a start button on the dashboard will allow the driver's car to start. Both these actions begin an authorization presses with a fob in the driver's pocket or purse. A low-frequency (LF) signal from the car awakens the fob. This is called the LF downlink. The fob measures the field strength vectors and sends the data back to the vehicle. Since the fob orientation is arbitrary, it must measure the field in the X, Y, and Z axes. This provides 3D data which can localize the fob as being either inside or outside of the car. If the system determines the fob is outside, it unlocks the door. If the system senses the fob being inside the car, it starts the engine.

Important to the design engineer is whether the LF field is well-regulated across power supply voltage, temperature, and part-to-part variation in the sense coils. Equally important is the accuracy of the LF field strength measurement. Finally, the fob should be highly sensitive to the field in order to allow the best range and noise immunity.

Features and benefits

  • Support for open standard Advanced Encryption Standard (AES) algorithm provides robust security
  • Highly integrated solutions typically integrate an Atmel microcontroller and result in small package size
  • PEPS key fob devices operate down to 1.9V and consume only minimal current extending battery life.  These ICs have market leading low-frequency (LF) receiver performance allowing the detection of smaller signals which means the fob is able to operate at a larger distance from the vehicle.
  • LF base station is loaded with market leading capabilities:
    • Scalable coil drive capability from 4 to 8 coils means optimal utilization for your application.
    • Programmable wave shape control mitigates EMC issues. 
    • Fast boost convertor means quick and accurate LF field strength measurements across wide operating voltage range.
    • Self polling feature supports “approach lighting”.
    • Buffer mode uses a buffer that is large enough to hold entire PEPS message.
    • Configurable I/O reduces host microcontroller overhead and simplifies design. 
    • Lower operating voltage and sensitivity to smaller signals means reliable operation across extreme system operating conditions.
    • High selectivity means greater immunity to interference.
    • High Rx and SPI (serial peripheral interface) data rates enable faster system response times. 
    • Buffered mode reduces software overhead on the host microcontroller.
    • Integrated features eliminate external components such as crystal and VBOOST control. 
    • PEPS/Immobilizer coil sharing eliminates one system coil. Both simplify design effort, save space and cost, and improve reliability.

Atmel Products

Key Fob ComponentsDescription
ATA5790NHighly integrated ultra low-power AVR® MCU with LF functionally for Passive Entry and Passive Start car keys, AES-128 encryption, industry's low current consumption, 1.5mVpp, QFN38 package (5mm x 7mm)
ATA5831Embedded AVR® Microcontroller Including RF Transmitter and Complete LF Functionality for Passive Entry/Passive Start Keys
Car Side ComponentsDescription
ATA5291Antenna Driver for up to Eight LF coils and Immobilizer base-station for PKE systems
ATA5279CAntenna Driver for Six Antennas
ATA5782Low-power RF Receiver for RKE, PEG, RS and TPMS Systems. Firmware Included in ROM, Additional Flash Option
ATA5831Embedded AVR® Microcontroller Including RF Transmitter and Complete LF Functionality for Passive Entry/Passive Start Keys