Automotive Central Body Control Module Block Diagram

Design Considerations

The Automotive Central Body Controller supervises and controls functions related to the car body such as lights, windows, door lock and works as a gateway for CAN and LIN networks. Load control can either be directly from the DBM or via CAN/LIN communication with remote ECUs. The central body controller often incorporates RFID functions like remote keyless entry and immobilizer.

 Power Management: The power supply is connected to the 12V or 24V board net and regulates down/up to voltages for DSP, uC, memory and ICs and functions like driver ICs, LF and UHV base stations and the various communication interfaces. The need for many different power rails makes the design of the power supply a critical task when trying to design for size, cost and efficiency. Linear regulators with low quiescent current help reduce battery leakage current during standby operating modes (ignition off), are load dump voltage tolerant for directly battery connected devices, and need low drop out and tracking for low battery crank operation.

Beyond providing increased conversion efficiencies, switching power supplies provide EMI improvement with slew rate control of the switching FET, Frequency hopping, spread spectrum or triangulation method for attenuation of peak spectral energy, Low Iq, soft start for power sequencing and in rush current limitation, Phased switching for multiple SMPS's regulators to minimize input ripple current and lower input capacitance, higher switching frequency for smaller components (L and C's), and SVS functions for brown out indications.

Communication Interfaces: Allow data exchange between independent electronic modules in the car, as well as remote sub modules of the Central Body Controller. High Speed CAN (up to 1Mbps, ISO 119898) is a two wire, fault tolerant differential bus. With a wide input common mode range and differential signal technology it serves as the main vehicle bus type for connecting the various electronic modules in the car with each other. LIN supports low speed (up to 20 kbps) single bus wire networks, primarily used to communicate with remote sub functions of the infotainment system.

Load Drivers: The main load driver types in a central body controller are lights and relay drivers. Often the switches and drivers for the exterior lighting are placed on the controller directly. Relays are used to power other electronic modules or high power loads. Current monitoring supervises demand from the distributed loads, other ECUs and can be used for charge and load management of the car battery.

RFID Functions: The two most common automotive RFID functions are the immobilizer and the remote keyless entry system. TI provides the LF base station IC for encrypted communication with the ignition key (immobilizer) as well as the Ultra Low power sub 1-GHz UHF transceiver for communication with the remote control for locking/ unlocking the doors and the alarm system.

Microcontrollers: The uC works as gateway for the bus and network interfaces and controls the various load drivers in the central body controller.

The Safety MCUs offer an ARM Cortex-R4F based solution and are certified suitable for use in systems that need to achieve IEC61508 SIL-3 safety levels. These MCUs also offer integrated floating point, 12 bit ADCs, motor-control-specific PWMs and encoder inputs via its flexible HET Timer co-processor. Hercules Safety MCUs can also be used to implement scalar and vector-control techniques and support a range of performance requirements.

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