Energy Saving with Microchip’s Newest CAN Partial Networking Transceivers
Carbon dioxide (CO2) is the primary component of greenhouse gases and one of the larger sources of emissions. Cars that use fossil fuels, such as gasoline and diesel, contribute about 12% to these emissions. Governments around the world have set mandatory emission-reduction targets for new cars. This legislation is the cornerstone of the strategy to improve the fuel economy of cars. Vehicle manufacturers face a dilemma. On the one hand, regulations continuously are calling for massive reduction of CO2 emissions, and, on the other hand, the use of electronics in vehicles is increasing rapidly, which results in increasing electrical power consumption. Today’s complex vehicles require more features, and the number of necessary electronic control units (ECUs) is increasing significantly. Many of the ECUs, even if they are not in use, are permanently active and consuming energy. A modern car can have more than 70 ECUs, though many of the ECUs are used quite rarely. The potential waste of energy, and with it fuel, results in a considerable increase in CO2 emissions.
Innovations in automotive electronics are essential for reaching the goals for CO2 reduction set by governments around the world. One of these innovations is CAN partial networking. Since the majority of network nodes today in a car are CAN nodes, one of the biggest savings opportunities is in CAN networks.
During sleep mode, a standard CAN transceiver will interpret any CAN communication as a wake-up event and will leave the sleep mode. Therefore, it is not possible for the device to stay in sleep mode while CAN communication is ongoing. This gap which is filled by the new generation of CAN transceivers offers selective wake-up functionalities.
With partial networking, one ECU or a cluster can remain in selective sleep mode, even in the case of ongoing CAN communication, without wasting energy, when the vehicle does not require it. Partial networking enables the use of dedicated and predefined CAN messages, instead of any bus activity, to wake up a node or a cluster. With partial networking, all vehicle functions remain available at any time, and the approach requires no modification of network architecture and no additional components or external crystals. But, from a CAN- transceiver manufacturer’s point of view, a big change is necessary, and this change will bring more complexity to the simple CAN transceiver. In addition to the standard transceiver functionality, a partial networking solution requires a high-precision oscillator, a CAN message decoding unit, an error handling management, a wake up frame configuration, compare unit, etc. Blocks that are not necessary with a simple CAN transceiver, are essential for a CAN partial networking transceiver.
The following describes the interaction of various new transceiver parts:
- When the CAN partial networking transceiver is in the selective wake-up mode with configured wakeup frame, the decoding unit will use an internal high-precision oscillator to decode the incoming CAN communication.
- Compare logic compares the decoded frame with the configured frame.
- If the decoded frame and the configured frame match, a wake-up event will be triggered, which will cause a change in the transceiver state and an interrupt will be generated to wake up the local microcontroller.
- In case of erroneous communication on the bus or faulty decoded frames an error management will detect this and increment the error counter.
- If the receive error counter overflows, the transceiver will wake up.
In order to help ECU developers optimize their designs for an emissions-conscious market, Microchip now offers a CAN partial networking transceiver that is fully compliant to the existing ISO11898-6 and the upcoming ISO11898-2 (2016) standards, the ATA6570.
The new CAN partial networking transceiver is able to monitor the CAN bus lines autonomously without the module’s main processor being active, which means that the ECU can be put in a deep-sleep mode with an overall current consumption of less than 30 µA. The automatic voltage biasing turns off the biasing of the CAN bus lines if there is no communication on the bus. The device is able to keep the complete ECU in low-power mode, even when bus traffic is present, until a valid wake-up frame is received. The biasing turns on automatically as soon as a valid wake-up pattern is seen on the bus. A dedicated interrupt signal informs the microcontroller about incoming CAN messages. By allowing parts of the CAN network to be deactivated in this way, the transceiver helps to reduce overall electrical energy consumption.
Configuring of the individual wake-up message, setting parameters and controlling state transitions are facilitated by a Serial Peripheral Interface (SPI) to the ECU’s microcontroller. The transceiver guarantees that both partial network transceivers and conventional high-speed CAN transceivers can be operated together in one network.
In addition to the CAN partial networking capabilities of the Microchip ATA6570 device, it can also function as a CAN-FD device enabling CAN bus data rates up to 5 Mbps. It can be easily configured via the SPI as Non-FD (meaning only for classical CAN), CAN FD silent, CAN FD passive or as CAN FD active device, in order to fulfill the corresponding application requirements.
An advanced fail-safe feature set is also implemented, which improves the sustainability and reliability of ECUs. Built-in features, such as supervision of the microcontroller, monitoring of the different supply voltages and chip temperatures, together with a CAN bus protection, provide predictable behavior in most common failure cases.
In addition, a watchdog with an independent clock source is also on board. It can be operated in window and in timeout mode with an optional cyclic wake-up. In the ATA6570 the dedicated reset pin is a high-voltage wake input used for waking up the device from sleep mode. It is usually connected to an external switch in the application to generate a local wake up.
All these features make the Microchip ATA6570 an excellent choice for high-speed CAN networks, especially in applications where nodes are always connected with the battery but are only activated when they are really needed in the application.
The new maximum allowed CO2 emission limit per km cannot be achieved only with the optimization of conventional technologies. New more efficient and flexible power management methods are needed, as well as technical improvements, to avoid incurring significant financial penalties. Implementing CAN with partial network can improve energy management while decreasing electric power consumption. With partial networking a node or a cluster of nodes can remain in selective sleep mode without wasting energy when the respective tasks are not required.
Partial networking makes a potential saving of up to 2.6g CO2/km possible. The adoption of this method does not require modifications to the existing network architecture, and neither external crystals nor additional components at the nodes are needed, but the simple CAN transceiver has to be replaced by a more complex CAN partial networking transceiver.
But there are even more reasons why partial networking is an interesting approach. For example, charging an electrical vehicle’s charging. A communication link to the main ECU is required, however most of the ECUs connected to the bus do not necessarily need to be active, they can be selectively powered down. This is also true for applications like data transmission between a parked vehicle and mobile devices. These use cases also result in increased requirements regarding the operating life of the components. Partial networking can compensate for this, resulting in reduced costs.
As one of the leading companies in the in-vehicle market, Microchip has expanded its CAN portfolio with the fully ISO11898-6 compliant CAN partial networking transceiver, the ATA6570, to enable emission-reducing designs now demanded by the automotive market. This HS- CAN transceiver is able to communicate with CAN FD data rates of up to 5 Mbps, enabling an extremely wide range of CAN FD applications.