Automotive power requirements and solutions choose body network requirements and development trends Off-board high-power load drive and solution comparison solution: BCM with linear regulator 24 V power supply in 12 V power supply BCM adopts switching regulator body control network application high Integrated chip remote lock and unlock using high-sensitivity high-frequency transceiver with wake-up and sleep detection As people's demand for handling and comfort of the car continues to increase, more and more electronic devices in the car body, such as Electric rearview mirrors, central locking, glass lifts, headlights and many more advanced features.
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Figure 1: System architecture of a typical body control module (BCM).
Power requirements and options
An important step in the design of a typical body control module (BCM) is to determine the power requirements and choose the right power solution. In general, BCM requires an input voltage between -0.5 V and 32 V and an output voltage of 5 V or 3.3 V.
It is worth mentioning that there are more and more electric equipment in the car. If the quiescent current of the battery directly powered by the battery is not low enough, and the car is continuously parked for a long time, the car battery may not be restarted due to excessive discharge. Therefore, BCM design needs to consider quiescent current. In addition, automotive applications may often face high temperature environments, so power supplies are 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. The choice of which power supply depends on the specific application.
In terms of the power supply of the body control module, in the cars sold in the Chinese market, the car generally uses a 12 V power supply, while the truck and bus generally use a 24 V power supply. In the 12 V power supply BCM, it is recommended to use ON Semiconductor linear regulators, such as NCV4275A, see Figure 2.
The NCV4275A is a 5 V, 3.3 V/450 mA low dropout (LDO) linear regulator with reset and delay. This device supports programmable microcontroller reset and offers a variety of features such as overcurrent protection. Over temperature protection, short circuit protection, etc. In addition, a diode (MRA4005) is connected in series at position 1 in the figure below. This linear power supply effectively prevents reverse voltages of up to -42 V.
Parallel a Transient Voltage Suppressor (TVS) tube at position 2 can effectively prevent transient power load dump high voltage pulses and unstable power supply clutter up to +45 V, in compliance with 12 V automotive power systems ISO16750-2-2003 4.6 Overvoltage Test Specification.
In fact, a load dump can occur at the moment the car engine starts, causing the battery voltage to rise above 40 V. These features make the NCV4275A ideal for automotive body control module applications.
In fact, the NCV4275A is only one of ON Semiconductor's wide range of linear regulators for automotive applications. Other linear regulators are such as NCV8664/5, NCV4949, NCV8503/4/5/6, NCV4274A, etc. Ultra-low static power products with quiescent currents as low as 30 μA and drive currents ranging from 100 mA to 450 mA.
Figure 2: Schematic diagram of a typical application circuit for a linear power supply in a body control module.
In a BCM application with a 24 V supply, it is necessary to convert the 24 V voltage to 5 V or 3.3 V. If a linear regulator is used, the power chip itself will have a high power consumption, and a large amount of heat will cause the temperature to be too high and burn out. Chips, so we need to use switching regulators, we recommend the use of ON Semiconductor's switching regulators for automotive applications such as NCV51411, NCV8842, NCV8843, NCV33063, NCV33163, NCV3063, NCV3163, LM2576, LM2575 and NCV2574.
These switching regulators have high efficiency, avoiding a large amount of heat release, protecting the chip and improving system reliability. The switching regulator drive currents for these automotive applications are mostly between 0.5 A and 1.5 A, some 2.5 A (NCV33163), and switching frequencies between 50 kHz and 300 kHz. Taking the NCV51441 as an example, this device uses the V2 control architecture to provide unparalleled transient response, excellent overall regulation accuracy, and the simplest loop compensation.
The “BOOST†pin on this device supports “Bootstrapped†operation to maximize energy efficiency; the integrated synchronization circuitry supports parallel power operation or minimizes noise.
Body network requirements and development trends
There are many types of system buses that can be used in automobiles, such as Controller Area Network (CAN), Local Interconnect Network (LIN), and FelxRay. The characteristics of these buses vary. 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.
Figures 3a) and b) show typical circuits based on the ON Semiconductor CAN transceiver AMIS-42665 and the LIN transceiver NCV7321, respectively. It is worth mentioning that the AMIS-42665 provides a very low quiescent current of less than 10 μA. Supports bus wake-up, common mode voltage range -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 is capable of withstanding a 5 kV ESD pulse. These devices offer powerful protection.
Figure 3: Typical CAN circuit (Figure a) and LIN circuit (Figure b) based on ON Semiconductor transceivers.
In the body control network application, it is necessary to reduce the cost and space requirements as much as possible, and at the same time improve the stability and long-term reliability of the system, so it is necessary to improve the integration of components. Thanks to the mixed-signal processes that have 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. The NCV7420 integrates a linear regulator and a LIN transceiver. This integration effectively saves PCB space and can separately supply power to the MCU, effectively curbing the interference of other modules on the MCU power supply.
ON Semiconductor has introduced an ultra-highly integrated chip, the NCV7462, for automotive body control network applications. The chip integrates a linear regulator, CAN transceiver, LIN transceiver, watchdog (WD) circuit, low-side drive and high-side drive to minimize the number of external components required, taking up very little Board space and help streamline 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 433 MHz (Europe) frequencies to achieve remote locking and unlocking through high frequency reception and transmission.
The design challenge in this type of application is to design impedance matching circuits to minimize power loss.
Requirements for such applications include low quiescent current, providing sleep mode, low transmit power, high receive sensitivity, low power consumption, and a suitable frequency range. And ON Semiconductor's ON-53480 high-frequency transceiver meets these design requirements, such as quiescent current as low as less than 1 μA, with wake-up and sleep detection, signal levels of only 10 dBm, and low receiver sensitivity. At -100 dBm with an operating current of only 10 mA and a frequency range of 280 to 343 MHz.
Off-board high-power load drive and program comparison
The body control module board needs to power some of the high-power loads outside the board, including automotive interior lighting (5 W and 10 W), one-way motors, and car speakers.
An alternative is to use an in-board relay. The coil of the relay is an inductive load, and the inductive load requires a starting current greater than the current required to maintain normal operation at startup, and the inductive load generates a back electromotive force at the moment of turning on or off the power. To drive the relay, use a relay driver such as ON Semiconductor's NUD3124, NUD3160 or NCV7608.
Table 2: Comparison of advantages and disadvantages of off-board high-power load drive scheme
Another option is to use a "pre-driver + MOSFET" to drive off-board high-power loads. The pre-driver can be implemented with ON Semiconductor's NCV7513A, which supports parallel port and SPI port communication, programmable, and provides failure mode detection and short-circuit. And open circuit diagnostics.
The third option is to use a SmartFET driver. This is a protected MOSFET that adds a number of features to the MOSFET, such as overvoltage clamping, ESD protection, overcurrent protection, overtemperature protection, backpressure protection, and high-side and low-side drivers. Typical devices are the low-side drive NCV8401/2/3 and the NCV8450 and NCV8460 for high-side drive (with integrated boost circuit). The advantages and disadvantages of these three schemes are shown in Table 2.
Other solutions for BCM
In addition to the above-mentioned high-power off-board loads, the electric motorized mirrors commonly used in automotive applications can use ON Semiconductor's NCV7703 to drive the steering motors. The device provides three half-bridge outputs with an output current of 0.6 A and up to 1 A, and features self-diagnostics that provide low quiescent current, SPI communication, and low/overvoltage/overtemperature protection.
In addition, the body control module needs to collect dozens of signals such as doors, locks, combination switches, etc., often need to expand the input port of the MCU, which requires a parallel port to serial port logic conversion chip, commonly used is 8 of ON Semiconductor Bit shift register MC14021B.
ON Semiconductor also offers different solutions for combined taillights. For example, the NCV7680 is an 8-channel low-side constant current driver that can set the tail travel/brake current output in pulse width modulation (PWM) mode, while the NSI45xx is a new constant current linear regulator (CCR) based on Anson. US Semiconductor's patent-pending self-biased transistor technology provides high performance with low cost, robustness, and the like, with a view to replacing the resistive drivers used in some automotive taillights.
The demanding body control module (BCM) imposes higher requirements on components. This paper deeply discusses the requirements of BCM design in power supply, body network and off-board high-power load drive, and compares the advantages and disadvantages of different solutions in some fields.
ON Semiconductor offers robust protection, high reliability, low quiescent current solutions for automotive applications such as body control modules such as power regulators, bus transceivers, high frequency transceivers, relay drivers, pre-drivers, motor drives, LED drivers and MOSFETs help designers to choose the best component solutions for their BCM designs, thus gaining an edge in the market.
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