Body control module design requirements and solutions

As people's demands for car handling and comfort continue to increase, there are more and more electronic devices in car bodies, such as electric rearview mirrors, central door locks, window lifts, headlights and even other more advanced functions.

Figure 1: Typical body control module (BCM) system architecture

Power Requirements and Solution Selection

An important step in the design of a typical body control module (BCM) is to determine the power requirements and select a suitable power solution. Generally speaking, the input voltage required by BCM is between -0.5 V and 32 V, and the output voltage is 5 V or 3.3 V.

It is worth mentioning that there are more and more electrical devices in the car. If the static current of the device directly powered by the battery is not low enough, and the car is parked for a long time, the battery in the car may be over-discharged and the car cannot be restarted. Therefore, the static current needs to be considered in the design of BCM. In addition, high temperature environments may often be faced in automotive applications, so the power supply is required to provide over-temperature protection.

Power supplies suitable for BCM include linear power supplies (or linear regulators) and switching power supplies (or switching regulators). These two power supplies have their own advantages. Which power supply to choose depends on the specific application.

In terms of the power supply of the body control module, among the cars sold in the Chinese market, cars generally use 12 V power supplies, while trucks and buses generally use 24 V power supplies. In the 12 V power supply BCM, it is recommended to use ON Semiconductor's linear regulator, such as NCV4275A, as shown in Figure 2.

NCV4275A is a 5 V, 3.3 V/450 mA low-dropout (LDO) linear regulator with reset and delay functions. This device supports programmable microcontroller reset and provides multiple features, such as overcurrent protection, overtemperature protection, short-circuit protection, etc. In addition, a diode (MRA4005) is connected in series at position 1 in the figure below, and this linear power supply can effectively prevent reverse voltages up to -42 V.

A transient voltage suppressor (TVS) tube is connected in parallel at position 2, which can effectively prevent transient power supply load dump (load dump) high-voltage pulses and unstable power supply noise up to +45 V, in line with the ISO16750-2-2003 4.6 overvoltage test specification for 12 V automotive power systems.

In fact, load dump may occur at the moment of starting the car engine, causing the battery voltage to rise to more than 40 V. These features make NCV4275A very suitable for automotive body control module applications.
In fact, NCV4275A is only one of ON Semiconductor's wide range of linear regulators for automotive applications. Other linear regulators include NCV8664/5, NCV4949, NCV8503/4/5/6, NCV4274A, etc. Ultra-low static power consumption products, static current as low as 30 μA, drive current range between 100 mA and 450 mA.

Figure 2: Typical application circuit diagram of linear power supply in body control module

In the BCM application of 24 V power supply, the 24 V voltage needs to be converted to 5 V or 3.3 V. If a linear regulator is used, the power chip itself will have a high power consumption, generate a lot of heat, and cause the temperature to be too high and burn the chip, so we need to use a switching regulator. We recommend using ON Semiconductor's series of switching regulators for automobiles, such as NCV51411, NCV8842, NCV8843, NCV33063, NCV33163, NCV3063, NCV3163, LM2576, LM2575 and NCV2574.

These switching regulators have high efficiency, avoid generating a lot of heat, protect the chip, and improve system reliability. Most of these switching regulators for automotive applications have a driving current between 0.5 A and 1.5 A, and some reach 2.5 A (NCV33163), and the switching frequency is between 50 kHz and 300 kHz. Take NCV51441 as an example. This device uses V2 control architecture to provide unparalleled transient response, excellent overall voltage regulation accuracy and simplest loop compensation.

The "BOOST" pin on this device supports "bootstrapped" operation to maximize energy efficiency; the integrated synchronization circuit supports parallel power supply operation or minimizes noise.

Body network requirements and development trends

There are many system buses that can be used in automobiles, such as controller area network (CAN), local interconnect network (LIN) and FelxRay. These buses have different characteristics. Table 1 compares several common system buses in automotive applications and lists typical ON Semiconductor bus transceiver products.

Table 1: Comparison of different automotive buses and typical transceivers

Figure 3a) and b) show typical circuits based on the ON Semiconductor CAN transceiver AMIS-42665 and LIN transceiver NCV7321, respectively. It is worth mentioning that the AMIS-42665 provides an extremely low quiescent current of less than 10 μA. It supports bus wake-up, a common-mode voltage range of -35 V to +35 V, and can withstand electrostatic discharge (ESD) pulses rated at +/-8 kV. The NCV7321 supports a voltage range of -45 V to +45 V and withstands ESD pulses rated at 5 kV. These devices all provide strong protection features.

Figure 3: Typical CAN circuit (a) and LIN circuit (b) based on ON Semiconductor transceiver

In the application of body control network, it is necessary to reduce the cost and space requirements as much as possible, while improving the stability and long-term reliability of the system, so it is necessary to improve the integration of components. Thanks to the mixed signal technology that has emerged in recent years, such as ON Semiconductor's Smart Power high-voltage BCD process, high-voltage analog circuits can now be integrated with low-voltage circuits, enabling the development and application of higher-integration system chips.

For example, ON Semiconductor's NCV7440 integrates a linear regulator and a CAN transceiver on the same chip, while NCV7420 integrates a linear regulator and a LIN transceiver. Such integration effectively saves PCB board space, can power the MCU separately, and effectively curbs the interference of other modules on the MCU power supply.

ON Semiconductor has launched an ultra-high integration chip for automotive body control network applications - NCV7462. This chip integrates a linear regulator, a CAN transceiver, a LIN transceiver, a watchdog (WD) circuit, a low-side driver and a high-side driver, reducing the number of required external components to a minimum, taking up only a very small circuit board space, and helping to simplify the design process.

Remote locking and unlocking design requirements and solutions

The application of remote locking and unlocking in automobiles is becoming more and more popular. The body control module uses 315 MHz (US, Japan) or 433MHz (Europe) frequency to achieve remote locking and unlocking functions through high-frequency reception and transmission.

The design difficulty in such applications is to design impedance matching circuits to minimize power loss.

The requirements of such applications include low quiescent current, sleep mode, low transmit power, high receive sensitivity, low power consumption and suitable frequency range. The ON-53480 high-frequency transceiver from ON Semiconductor meets these design requirements well, such as quiescent current as low as less than 1 µA, wake-up and sleep detection functions, signal level of only 10 dBm, receive sensitivity of less than -100 dBm, and operating current of only 10 mA, with a frequency range of 280 to 343 MHz.

Off-board high-power load drive and solution comparison

The body control module circuit board needs to power some off-board high-power loads, including automotive interior lighting (5 W and 10 W), unidirectional motors and car horns.

An optional solution is to use an on-board relay. The coil of the relay is an inductive load, and an inductive load requires a starting current larger than the current required to maintain normal operation when starting, and an inductive load will generate a reverse electromotive force at the moment of powering on or off. To drive the relay, a relay driver such as ON Semiconductor's NUD3124, NUD3160 or NCV7608 can be used.

Table 2: Comparison of advantages and disadvantages of off-board high-power load driving solutions

Another solution is to use "pre-driver + MOSFET" to drive off-board high-power loads, where the pre-driver can use ON Semiconductor's NCV7513A, which supports parallel port and SPI port communication, is programmable, and provides failure mode detection and short circuit and open circuit diagnosis functions.

The third solution is to use SmartFET drive. This is a protected MOSFET, which adds multiple functions on the basis of MOSFET, such as overvoltage clamping, ESD protection, overcurrent protection, overtemperature protection, reverse voltage protection, and high-side and low-side drive. Typical devices include NCV8401/2/3 for low-side drive, and NCV8450 and NCV8460 for high-side drive (with internal integrated boost circuit). The advantages and disadvantages of these three solutions are shown in Table 2.

Other solutions for BCM

In addition to the above-mentioned off-board high-power loads, ON Semiconductor's NCV7703 can be used to drive the steering motor in the electric rearview mirror commonly used in automotive applications. This device provides three half-bridge outputs with an output current of 0.6 A and a maximum of 1 A. It also has self-diagnosis functions, low quiescent current, SPI communication, and low voltage/overvoltage/overtemperature protection.

In addition, the body control module needs to collect dozens of signals such as doors, locks, and combination switches, and often needs to expand the input port of the MCU, which requires a logic conversion chip from a parallel port to a serial port. The commonly used one is the 8-bit shift register MC14021B from ON Semiconductor.

ON Semiconductor also provides different solutions for combination taillights. For example, the NCV7680 is an 8-channel low-side constant current driver that can set the tail driving/braking current output in a pulse width modulation (PWM) manner, while the NSI45xx is a newly launched constant current linear regulator (CCR). Based on the self-biased transistor technology of ON Semiconductor's pending patent, it provides high performance with low cost and ruggedness, and aims to replace the resistor-type drivers used in some automotive taillights.

The body control module (BCM) with harsh application environments places higher requirements on components. This article deeply explores the requirements of BCM design in power supply, body network and off-board high-power load driving, and compares and analyzes the advantages and disadvantages of different solutions in some fields.

ON Semiconductor provides solutions with strong protection characteristics, high reliability and low quiescent current for automotive applications such as body control modules, such as power regulators, bus transceivers, high-frequency transceivers, relay drivers, pre-drivers, motor drivers, LED drivers and MOSFETs, etc., to help designers choose better component solutions for their BCM designs, so as to gain an advantage in the market.