Dc motor body electronics applications

The content of electronic products in the in-car system continues to grow due to the increasing market demand for automation, safety, energy efficiency optimization and high-quality experience.Against this background, the number of applications using dc motors is also increasing.

This article will analyze the trends in the automotive dc motor market and explain why solid state drives (SSDS) are a good design framework for diagnostics, optimization of switching time, weight reduction, and (most importantly) increased reliability.

We also will be particularly explained why in all designed for automotive dc motor control of the fully integrated circuit design, new VIPower ™ M0-7 H bridge series can be with the best choice.

The market trend

It is estimated that the demand for automotive dc motor system will grow steadily, with the annual growth rate of about 3.1% in the next five years.The demand around the car body comes mainly from traditional applications such as door locks, electric rear mirrors, seat adjustments, cleaner pumps, windshield wipers, window switches, skylights and electric sliding doors.But there are also a number of new and very attractive applications coming to market, some of which include head-up displays (HUD), hidden door handles, electric tail doors, electric car shifters and electric car charger locks.

Considering the above situation, it is estimated that the worldwide demand for body-related dc motors will reach 2 billion in 2020.

The figure below shows the proportion of various applications, all of which consume between 30W and 200W.

A comparison of the use of relays and built-in chips for driving dc motors in automotive applications

The automotive industry used to see relays as a simple and inexpensive solution for driving dc motors.But that thinking is changing, and automakers now see SSDS as a better fit for new app designs.Because of its highly reliable quality and enhanced diagnostic capabilities, SSDS can easily be built with innovative features such as driving variable load profiles (such as electric tailgate) or controlling motion smoothness (such as window switches or seat adjustments), eliminating relay switching noise, and adding luxury.

Most importantly, local legislatures around the world have begun to set new limits on the emissions of pollutants and carbon dioxide from automobiles, and the structure of automobiles must be adjusted, especially the supply of power loads, with more efficient electronic components.Although the impact of the new standard will be mainly on the power-train system, the Body Control Module (BCM) still has some relevance.

Therefore, we predict that the annual average growth of dc motors driven by SSDS will be 6.7% between 2020 and 2025, and the market share of relay will gradually increase.

In this case, stmicroelectronics' VIPowerTM m0-7 h-bridge series of products will be the best choice among the same class of components for motor control in automotive applications.The m0-7 h-bridge series integrates logic functions and power structures into a single package, enabling the built-in intelligent functions of the chip so that in addition to providing simple driving functions, it can also prevent failures, provide advanced diagnosis and protection functions, reduce the number of required parts, improve reliability and save the area of the printed circuit board (PCB).

Increased reliability extends service life by a factor of 10

Relay contacts are pieces of metal that conduct electricity and are connected to allow current to flow through them.Common problems with mechanical switching contacts include hearing noise and poor perception of mechanical vibrations by the end customer (especially in frequency-driven applications).In addition, the relay switch will cause arc noise, which will generate electromagnetic interference (EMI).Additional components (RC snubber and flywheel bond) should be required to reduce relay switching noise, but should be at least at least at the minimum.The electromechanical stress caused by switching will reduce the contact resistance and efficiency in the medium and long term, making the relay unable to be used or shortening its service life.Deterioration of relay performance reduces reliability.

Solid state switchers have no moving parts because the mechanical contacts have been replaced by transistors: there are no problems with arcing contacts, magnetic fields, or audible noise.Input control is compatible with most IC logic products without the need for additional buffers, drives or amplifiers.The result is increased reliability, up to a tenfold increase in switching time.

Small power package helps to save application area

As the car market evolves toward autonomous driving, more and more sensors and actuators must be used.It is easy to see why the restrictions on space are becoming more severe, given that more components must be packed into the same space.

The H bridge topology is usually used to drive the bi-directional dc motor: by alternately switching on and off the bridge, it is possible to control the motor direction or stop the motor.Although H bridge structures can be easily constructed using relays, SSDS can significantly reduce circuit board space.

Since the marking area of the general relay is about 250 mm2, a circuit board area of at least 500 mm2 is needed to construct the H bridge structure.In addition, discrete circuits, such as buffers, operational amplifiers and sensors, must be added to build high voltage transient suppression, system diagnostics and protection functions.These additional parts will greatly increase the final size and complexity of the circuit board, and will have a negative impact on the reliability of the application.

Finally, the design of the PCB cover and enclosure must also take into account the height of the relay, so as to maintain a vertical distance of 17 mm in general.

Taking into account the outstanding space-saving features of the VIPowerTM m0-7 technology, stmicroelectronics' h-bridge range enables the entire motor drive architecture to be built into advanced small power packs: so-16n and powersso-36.It can reduce the imprinting area of 60 mm2 and 106 mm2 respectively, and the thickness is less than 2.5 mm, making the printed circuit board smaller and the system can also reduce the weight.In addition, VIPower ™ M0-7 H bridge provide lead-free packaging environmental protection product portfolio, to ensure excellent cooling performance.

Switching time and pulse width modulation (PWM) control

When guiding the H bridge structure, special attention must be paid to avoid unnecessary short circuit between the battery cable and the ground, especially in the switching stage;This condition is usually defined as a dynamic breakdown.Whenever a breakdown event occurs, it will generate additional noise and power consumption of the battery line, thus reducing the system efficiency.If the H bridge is driven by a quick switch such as a PWM signal, the phenomenon becomes more serious.

PWM input signals are often used to control the h-bridge structure. By changing the operating cycle, motor speed and torque can be adjusted to build the following advanced functions:

· clamp-proof function;

· smooth start and stop actions to improve the driving experience;

· stall condition control;

· motor speed regulation is not affected by battery voltage;

Reduce the initial influx of current

The typical dc motor profile has a start-up period where the incoming current is 10-12 times the normal current.All electronic components must meet specifications to withstand such a high current for a period of time, which will continue to affect the final application wire size, PCB area and driver function.

It is true that the relay specification provides only the maximum contact rating for resistive dc loads, which can be substantially reduced by highly inductive or capacitive loads.

By using pulse width modulated signal to drive dc motor, a smooth motor start can be achieved under limited torque.The incoming current will also be reduced, extending the motor start-up period.By driving the dc motor with PWM signal, the power consumption can be optimized and the wire size can be reduced.

Relays are not suitable for systems that require quick output switching, which is limited by the movement of the mechanical tip, usually between 5 ms and up to 15 ms.In addition, the microcontroller (MCU) must have appropriate logical protections in place to prevent unwanted interactions from transmitting events.

The VIPowerTM m0-7 H bridge series guarantees fast switching times (usually 1 microsecond) up to 20 KHz.The toggle profile is specially designed to optimize emi and toggle loss.In addition, the chip is embedded with special protection functions to avoid dynamic and static interaction conduction problems.Therefore, the VNH7 series is designed to optimize system performance.

VIPowerTM m0-7 series H Bridges are used for dc motor control

VIPower ™ M0-7 H bridge series can be seen as driven dc motor vehicle natural options, can meet the market to improve reliability, system efficiency and the demand of the advantages of luxurious feeling.With a hybrid mode, the m0-7 H bridge series integrates logic functions and power structures into a single package, providing a complete portfolio of fully integrated and protected circuits.Because can provide different open (on - state) resistance (from 8 m Ω to maximum 100 m Ω) and power supply packaging small volume, this series of products can ensure the elastic drive and control functions, covers a wide variety of load condition (200 w) from low to high.

Although the middle and low power components integrate all logic functions and complete power stages, including high side and low side power metal oxide semiconductor (MOS), high power components like VNHD7008AY and VNHD7012AY adopt different architectures, including high side power MOS and low side gate driver.Therefore, an external low-side power MOS(STL76DN4LF7AG is recommended) is required to complete the H bridge architecture.

The 20-khz pulse width modulated speed control plus a diagnostic mechanism make the above products best suited for advanced automotive applications.Power consumption in standby mode is extremely low, up to 3 microamps (A), and the switching profile during conversion is optimized to keep module power consumption low, although it increases the number of electronic parts on the circuit board.

The combination of advanced diagnostics (VCC voltage, housing temperature and current load detection) and protection (over voltage, short circuit, high temperature and interactive conduction protection) protects both the power level and the load without affecting the final efficiency system, ensuring that the device is always operating within a safe operating area.In addition, thanks to the off state diagnosis function, the status of the motor can be monitored during the standby state to avoid possible damage when it is started.

In the body control module combination VIPower ™ intelligent power switch function and M0-7 H bridge driver, can save power consumption and area of printed circuit boards and wiring requirements.The practical results will be increased system reliability and an estimated reduction of up to 50kg per vehicle, which will have a positive impact on pollution, including reduced co2 emissions from internal combustion engine (ICE) vehicles (up to 3.5g/km), battery optimization, and improved autonomous driving for pure electric vehicles (BEV).