[Figure 2] Automotive PEPS system block diagram

Communication bus options

LIN (Local Interconnect Network) and CAN (Controller Area Network) are important communication bus architectures in automotive PEPS systems, and CAN is used as the CAN bus standard (Classical CAN) or CAN FD (Flexible Data Rate).

Both LIN and CAN are standard communication protocols widely used in automotive applications. The LIN communication system has a maximum baud rate of 19.2 Kbps, while Classical CAN offers 1 Mbps and CAN FD offers up to 5 Mbps.

LIN and CAN use message frames as the basis for establishing communication protocols, and data fields can transmit up to 8 bytes. The message frame length of LIN, which transmits 8 bytes, is 124 bits, while a standard CAN frame or CAN 2.0 frame can be up to 135 bits.

However, this assumes the worst-case bit stuffing, including interframe space. Therefore, the transmission speed of a LIN message frame is 6.46 ms, while a standard CAN message frame is only 135 µs, which is faster.

Which should I choose, LIN or CAN?

Based on the above transmission speed, LIN message frames take longer to process than CAN frames, so if you need faster transmission speeds, you'll likely choose the CAN bus. However, the CAN bus is a two-wire communication bus, while the LIN bus is a single-wire communication bus.

This means that CAN bus-based systems are more expensive than LIN bus-based systems, so CAN bus may not always be the best choice.

So which of these two protocols should you choose? One way to do this is to analyze the total number of bytes required for transmission.

If a Bluetooth low energy chip implements the computational algorithm in the satellite node, the number of bytes required to be transmitted can be reduced, so it can be satisfied with LIN communication alone.

On the other hand, if a Bluetooth low energy chip transmits all the raw measured data without any calculation, it would require a lot of bytes, making the CAN architecture a more suitable choice.

Another consideration is power consumption. LIN bus-based nodes typically consume less power than CAN buses in all operating modes. Specific power consumption figures can be found in each transceiver data sheet.

Application Cases

TI's Automotive Bluetooth Low Energy Car Access Satellite Node Reference Design demonstrates the implementation of a LIN-based satellite board. This reference design uses TI's CC2640R2F-Q1 as the Bluetooth Low Energy SoC and the TLIN1029-Q1 as the LIN communication bus transceiver.

When large amounts of data need to be exchanged between a smart key module and a Bluetooth low energy satellite module, the CAN bus standard or CAN FD bus architecture is most suitable.

CAN communication capabilities can be easily added to satellite nodes with TI's new TCAN4550-Q1 system-basis chip ( SBC ), which integrates a CAN FD controller and transceiver. In addition to the integrated controller and transceiver, the SBC is self-contained and requires no additional power supply.

Additionally, the SBC has a watchdog timer that acts as a system-on-chip (SoC) monitor and provides voltage supplies for additional power components on the printed circuit board.

[Figure 3] shows a satellite node that can be implemented using the TCAN4550-Q1, which utilizes the functions of this device.

[Figure 3] TCAN4550-Q1, which supports easy addition of CAN communication to satellite nodes.

In [Figure 3], the 5V output of the TCAN4550-Q1 is used as the input of the TLV733P-Q1 low VIN linear regulator.

This regulator generates the 3.3V required for the CC2640R2F-Q1 Bluetooth low energy SoC, eliminating the need for a wide VIN regulator for power supply.

3.3V regulator output is V for TCAN4550-Q1It can also be used as an IO, eliminating the need for voltage level conversion between the Bluetooth low energy SoC and the TCAN4550-Q1.

Additionally, the TCAN4550-Q1's watchdog timer can monitor the execution of Bluetooth low energy SoC software. This highly integrated SBC enables cost-effective implementation of Bluetooth low energy hygienic nodes.

conclusion

Now, Bluetooth low energy technology enables the implementation of next-generation PEPS systems in vehicles.

As developers grapple with the challenge of determining the optimal number of nodes required to meet PEPS requirements, the communication bus architecture plays a key role in the solution, with developers having a choice of communication protocols: LIN or CAN.

TI's LIN transceivers and the newly introduced TCAN4550-Q1 SBC, along with Bluetooth low energy SoCs and power management devices, provide a complete portfolio of devices to choose from as well as the flexibility to develop solutions optimized for automotive platforms.