Defining the LF Driver’s Main Parameters in Automotive PEPS Systems

By Dr. Jedidi Kamouaa

Passive entry passive start (PEPS) systems, already well established in the high-end car market, are the latest trend in mid-price vehicles. Strategy Analytics anticipates annual demand for PEPS systems to reach almost 19 million units by 2016. This trend is fueled by cost savings from a reduction in the number of coils per vehicle, the greatest contributor to system cost.

PEPS system design presents a number of challenges:

• Generation of high drive current and, thus, the low-frequency (LF) magnetic field required to detect the key fob inside the vehicle or in the near vicinity
• Drive-current regulation to allow reliable receive signal strength indicator (RSSI) measurement
• Protection under thermal stress conditions and electrical diagnostics
• Reduction in electromagnetic radiation
• PEPS system speed

 A key part of PEPS systems is the LF driver. The Atmel ATA5279C multichannel LF antenna driver IC includes technical features to meet PEPS system requirements. It operates alongside the Atmel ATA5791 single-chip key fob controller, integrating the RF transmitter.

When developing an LF antenna driver system, you’ll need to consider:

• Capability to generate sufficient magnetic field to detect the key fob inside the vehicle or in the vicinity of the vehicle
• Use of a regulation loop of the drive current for reliable field strength and thus RSSI measurement
• Protection under thermal stress conditions and electrical diagnostics
• Electromagnetic radiation
• The interface with the host microcontroller
• Thermal factors

With the need for cost savings, car makers also expect the LF driver to perform the immobilizer backup function, which requires the merging of the immobilizer and LF driver functions, multiplexing one of the antennas and thus eliminating one coil (a major cost contributor). This merger allows the immobilizer base station coil in the steering lock cylinder to be removed, and the resulting change in car architecture will enable significant cost savings that should further increase PEPS system adoption.

For diagrams and detailed information about how to define the LF driver, see the article “How to Define the LF Driver’s Key Parameters in Automotive PEPS Systems.”