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비디오 시리즈

Precision labs 시리즈: 모터 드라이버 설계

다른 애플리케이션별 아날로그 집적 회로와 마찬가지로 모터 드라이버에는 주요 설계 고려 사항이 있습니다. 이러한 중요한 주제에 대해 알면 강력하고 효율적인 시스템을 설계하는 데 도움이 될 수 있습니다. 이 비디오 시리즈에서는 모터 드라이브 회로를 설계할 때 고려해야 할 주요 고려 사항에 대해 설명합니다.

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      발표자

      [MUSIC PLAYING]

      Welcome to the Texas Instruments Precision Labs Design 1 session, Selecting a Motor Driver. My name is Hector Hernandez. I am an applications engineer of the Texas Instruments Motor Drivers team. In this video, we look at what to consider when selecting a motor driver.

      Educated motor drive selection is an integral part to any motor drive application design. Proper part selection can reduce cost and debugging time. Motor drivers can increase system efficiency, smoothness, and performance when compared to discrete motor drive solutions. The first thing to consider when selecting a motor driver is the type of motor for the end application.

      Let's get started. Brushed DC motors, frequently called the BDC motors, are easy to drive motors due to the relatively simple control scheme they require and have a low construction cost due to the use of metallic brushes. These motors, however, wear down quickly due to the mechanical rubbing of the brushes, and they produce sparks. Additionally, BDC motors generate higher electromagnetic radiation when compared to motors that don't require brushes.

      When an application requires a cost-effective motor with a simple drive circuitry, brushed DC motors can be utilized. These motors are found in many solutions, such as household applications like gate openers or electronic locks; consumer products, such as battery powered robotic toys; automobile body applications like power seats, power windows, and power trunk lifts; shut off valves found in gas meters and water meters; and insulin pumps, along with many other medical applications.

      Stepper motors are also low cost motors that have a simple control interface, although not as simple as a brushed DC motors. The downsides to using these motors include higher audible noise, resonance effects, high temperature operation, and inefficiency. Despite these disadvantages, stepper motors are excellent for applications that require precise movement or position control.

      Application examples include security cameras, paper movement and multifunction and laser beam printers, refrigerator dampers, electronic point of sale and banking automation applications, such as EPOS printers and ATM machines, and finally, adaptive or auto leveling headlights in vehicles. Brushless DC motors, or BLDC motors, have benefits that include a long lifetime and reliability due to the lack of contact between stator and the rotor. Additionally, the BLDC motors are the most efficient and can achieve a smooth drive.

      Many applications that historically use BDC motors have switched over to BLDC motors due to these benefits. The cons of these motors include two crucial disadvantages. They require a complex drive design, and its drive circuitry is more expensive than the other motor types. BLDC motors are used primarily and high-efficiency, servo, and variable speed applications, such as quiet and efficient pumps and fans in home appliances, cordless vacuum cleaner suction motors, e-bike drive motors, pump transmission, electric power steering, and braking motors in vehicles, and high-output power and gardening tools.

      Motor drivers for BDC, stepper, and BLDC motors are substantially different from each other. So make sure to focus on the motor types that apply to your design. One key parameter to consider during the selection process is the voltage. The supply voltage is commonly written as VS, VM, PVDD, VBB, or VBAT.

      In any motor drive system, there is some supply that will be the power source for the motor drive. These supplies can take many forms but are primarily plug-in or battery. Plug-in sources take the high voltage AC from a wall outlet and transform it to a lower voltage-- for example, 24 or 12 volts.

      In any system, there will be a typical supply voltage with some variation-- for example, a regulated 24 volts with a plus or minus 10% in operation. Batteries typically have a usability range-- for example 14 to 21 volts for a 5-cell lithium-ion stack. Some applications have wide operating ranges due to the multiple influences on the supply line, like in the case of a lead acid battery in a car.

      When a brushed DC motor is starting to spin, the inrush draw is very high and can cause a supply to droop as extra energy is drawn from the system. There is no specific number to give guidance in the minimum and maximum voltage requirement, since it will depend heavily on the motor type, motor driving technique, supply capabilities, and size of bulk capacitance utilized.

      There are two different types of current to consider, peak current and RMS current. Peak current is the maximum short duration current in a motor that can be caused by switching events, inrush, or parasitic effects. Since many motor drivers integrate overcurrent protection, we want to make sure that this protection mechanism is not tripped during normal operation of the motor.

      The peak current in a motor driver is specified by the maximum current that can be driven before the overcurrent protection kicks in. If a so-called peak current lasts longer than tens of milliseconds, you should take warning because the motor driver can heat up very quickly. Take care of that you do not exceed the thermal limits of the device.

      RMS current, which is also called average or continuous current, is the nominal current of the motor. The power dissipation in the motor driver is largely determined by this RMS current. However, be careful if this parameter is specified. The amount of RMS current that a part can actually drive will be very dependent on the thermal characteristics of the circuit board and system, including the copper thickness, the number of layers, the layout pattern, and the presence of airflow.

      If you are designing a high power system, it may be difficult or impossible to find a motor driver to meet your current output needs. This means that you need to use a gate driver. Motor drivers can come in two forms, the integrated driver or the gate driver.

      Integrated drivers include the MOSFET power stage, MOSFET control, and/or any other circuits, like protection, power management, and current sensing, into one package. This results in a small solution size, which can easily be designed into most systems. The downside to this all-in-one solution is power and heat.

      An integrated driver will not be able to drive very high power, since the integrated MOSFETs are limited in size, and all the power dissipation is concentrated into one package. Integrated FET drive capability is typically specified by peak current, in amps, and on resistance, sometimes called RDS(ON). Gate drivers require the MOSFET power stage to be implemented externally. And the gate driver controls the external MOSFETs to drive current into the motor.

      These solutions can be efficient and very high power, using external MOSFETs with very low on resistance to drive kilowatt motors. Designers can choose the external MOSFET to best meet their motor needs. And they can scale the system power as needed. Gate drivers by nature will require a larger solution size when compared to integrated drivers and have a more complicated schematic and layout effort due to the multiple components involved.

      Gate driver system power is dependent on the external MOSFET used, but the gate drive current is an indicator of drive capabilities of the motor driver. Gate drivers can support higher power due to the externalization of the FETs. They have better thermal performance, and the power is more selectable and scalable. The important parameter to consider when selecting a motor driver is the gate drive current.

      As a closing comment, motor drivers and integrated circuits in general have various ratings for different applications. Catalog devices are tailored for high volume commercial applications. These applications include personal electronics, industrial, telecommunications, and enterprise applications. Automotive devices have high reliability and are for automotive applications. Extra qualification and process monitors are added as per the automotive quality requirements.

      Enhanced products are built with enhanced material sets for harsh environments. Military and space products are ceramic parts released to a MIL spec. They are intended for extreme environments, long lifetimes, high reliability, and long-term dormant storage. Motor drivers are available with several operating temperature ranges-- commonly, negative 40 Celsius to 85 Celsius or 125 Celsius. Automotive products, additionally, can support up to 150 Celsius for stringent automotive Grade 0 requirements.

      Additionally, enhanced products, as well as military and space products, extend the temperature range down to negative 55 Celsius. Thanks for watching. To find more motor driver technical resources and search products, visit TI.com/motordrivers.

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      Precision labs 시리즈: 모터 드라이버 설계