In automotive applications, the typical Local Interconnect Network (LIN) node has a limited set of functions such as monitoring mechanical switches or touch buttons on a steering wheel and sending the information to the connected LIN master. For tasks like these that involve minimal computing, the primary design factors are low cost and size constraints. However, as multiple Embedded Control Units (ECUs) are being integrated into modern cars, power consumption for each module needs to be optimized.
While new technologies like CAN Partial Networking (CAN-PN) are introducing new methods to reduce power consumption on a bus-wide level, it is also important to equip microcontrollers (MCUs) with the right peripherals and functionalities to allow for very-low static power consumption for ECUs that are in standby while the ignition is off. Space is another concern. As more ECUs are used in vehicles to offer additional functionality, the modules need to become smaller and lighter. It is crucial to optimize devices so they can be used to create small ECUs.
As designers face the necessity of developing increasingly complex LIN nodes while maintaining, or even reducing, the amount of space these nodes occupy, Microchip now offers a new family of low-power, multi-chip System-in-Package (SiP) devices to address these requirements. The SAM HA series of SiPs combines the performance and energy efficiency of a 32-bit Arm Cortex-M0 based microcontroller (MCU) and the optimized architecture and peripheral set of a feature-rich LIN System Basis Chip (SBC) with a fully integrated LIN transceiver.
The integration of these two functionalities within one package saves valuable board space and simplifies Printed Circuit Board (PCB) layout. Routing the TXD and RXD signals between the two Integrated Circuits (ICs) is not necessary, since this connection is made internally to free up pins for other I/O functionality. To provide flexibility in planning your system design, the two devices have separate power supplies. You can use the battery to power the whole system and use the internal voltage regulator with a 3.3V/85 mA output to supply the MCU and additional components on the PCB.
A broad set of peripherals is available to meet the requirements of a wide range of LIN applications. These include an integrated DMA controller and Event System. Many of these peripherals are highly optimized blocks that have evolved and been refined over many decades of MCU design and innovation. To provide you with additional flexibility for your design, each of the members of the SAM HA series of SiPs offers distinctive functionality and comes with up to 64 KB of Flash memory and 8 KB of RAM.
The first device to be introduced, the ATSAMHAxGxxA, is a general-purpose device offering a wide range of features in a small 48-pin QFN package. The recently released ATSAMHAxExxA is a 32-pin QFN device that measures just 5 mm × 5 mm and yet integrates all the functionality required for creating even smaller LIN nodes. Table 1 provides an overview of the features of both sets of devices. Note that they both provide the same LIN functionality but the number of peripherals available in the MCU varies by package size.
Event Detection and Power Management
The Event System allows autonomous, low-latency and configurable communication between peripherals. It can be used to trigger actions in other peripherals and to wake up the MCU without intervention from the CPU. Most peripherals can be configured to generate events and respond to events coming from other peripherals. To do this, a direct connection is made between two peripherals using one of the 12 available channels, which is then set aside solely for this event. This reduces the load on the CPU and other system resources as compared to a traditional interrupt-based system.
Peripheral Touch Controller
If you would like to implement a touch-enabled interface in your automotive application, some devices in the SAM HA series of SiPs include a Peripheral Touch Controller (PTC) that offers hardware support for capacitive touch recognition. The QTouch Library can be used to implement buttons, sliders, wheels and proximity detection. The PTC can be used in two modes. Self-capacitance mode allows a connection to one touch sensor per I/O pin, while mutual capacitance mode supports up to 90 channels by connecting them in a matrix to the X- and Y-channels. The number of available channels depends on which device in the family is used. No external components are needed to perform the touch acquisition in either mode. The difference is illustrated in Figure 1.
Serial Communication Interface
Providing excellent flexibility for automotive applications, the SAM HA series of SIPs offers up to five serial communication interface (SERCOM) peripherals. This innovative module is fully software configurable to handle I2 C, USART, LIN and SPI communications. Proven and qualified LIN stacks, available from various vendors, use the SERCOM to provide LIN functionality for one or more slave nodes on the same controller. To save power, the SERCOM can also be used to wake up the device from standby mode only if there is activity on the LIN bus. The device can wake up quickly enough to receive and respond to the first frame.
Microchip’s SleepWalking technology is another feature available in the SAM HA series of SiPs. Designed to minimize current consumption, SleepWalking allows a system to save power by only activating clocks when they are necessary for a peripheral to perform its function. While the device is in sleep mode, all the clocks are usually switched off to avoid unnecessary power consumption. The necessary clocks can be temporarily enabled without CPU intervention, allowing the CPU to remain in sleep mode for the whole process. The Event System and the SleepWalking capability can be combined to minimize power consumption as illustrated in the following example:
- The CPU is sleeping and a timer is triggering an Analog-to-Digital Converter (ADC) measurement every second via the Event System.
- When that trigger occurs, the ADC will turn on the clock necessary to run the ADC measurement and will turn it off when it is no longer needed.
- The ADC will compare the sampled value to the previously stored threshold and wake up the CPU if the sampled value is within the window.
- During this entire process, the CPU remains in sleep mode and the relevant clocks are only active when they are actually needed.
- Another benefit is that the latency between the timer elapsing and the actual processing of the event is shorter and deterministic as shown in Figure 3.
Integrated Voltage Regulator
Because of its very flexible peripherals, the SAM HA family of SiPs can address the requirements of a wide range of applications. For example, the integrated voltage regulator eliminates the need for external components to save costs, while reducing the footprint of the device to make it ideal for small modules.
The space-saving, integrated LIN-SBC has two functions. First, it provides a 3.3.V/85 mA low-drop voltage regulator that is intended to power the MCU and other devices on the module. This enables small modules to be powered entirely via the battery without the need for an additional voltage regulator. Second, it provides a LIN transceiver designed according to the LIN 2.2A, ISO17987 and the SAEJ2602-2 specifications. TXD and RXD are connected internally and only the bus pin needs to be routed on the PCB.
To get started with developing low-cost and yet highly integrated LIN-connected automotive applications using the new SAM HA family, visit our LIN System-in-Package Solutions page. For extra design flexibility, the two ICs used in these SiPs are available as standalone families of devices with additional variants. You can choose devices with different pin counts, devices without LIN functionality and devices with other options. This enables to you to reuse code as you develop similar applications with slightly different requirements. The SAM HA devices can be purchased from microchipDIRECT or from Microchip’s worldwide distribution network.