With the development of motor drives, the market has new requirements for motor drives - safer (stable operation, low failure rate), more environmentally friendly (high efficiency, low power consumption), and smarter (advanced algorithm, easy to use) . In the past, the motor drive was designed with discrete divisions. The board contained several sub-circuits such as pre-logic, MOSFET drive, clock, power management, temperature sensor, protection circuit, power supply control, comparator, and reference voltage (Figure 1). In this way, the board is large in size and the security is not high.
Not long ago, Texas Instruments (TI) introduced a 24V three-phase sensorless BLDC motor driver DRV10983. Texas Instruments China market development high-performance analog products business development manager Xin Benwei said that many motor applications now require more and more volume Small, requires the MCU and the drive circuit (including various protection circuits) to be fully integrated and implemented in the motor, which is also the future development direction of the motor.
Figure 1: Traditional discrete motor drive solutions require more than 100 transistors, digital gates, amplifiers, LDOs, temperature sensors, and fuses.
Texas Instruments has a wide range of motor drive products (including stepper motor drivers, brushed DC motor drives, brushless DC motor drives, solenoid drivers, and Hall effect sensor ICs) with over 15 years of design experience; customized The form is widely used in hard drives, optical drives, inkjet printers, digital cameras, automotive industries and other industries. Texas Instruments established the Motor Drive Division (MDBU) in 2010 and began to enter the mass market.
Xinbenwei pointed out that the motor drive is made into a highly integrated solution, which integrates the driver, MOS tube, protection circuit, control switch and algorithm. The advantages of this are: 1. Reduce the PCB size and reduce the BOM. 2, because of the high degree of integration, so the reliability is improved, the consistency of the entire circuit is very high; 3, customers do not need discrete design, directly with an IC can be product design. In addition, all of TI's motor drive products offer complete protection, including overcurrent/short circuit protection, overtemperature protection, undervoltage lockout, and breakdown protection.
In terms of protection, overcurrent protection is required between the ground, the power supply or the coil. Unlike current regulation circuits, TI products include another protection circuit "ILIMIT". ILIMIT is an algorithm for more complex hardware circuits. By reducing the gate voltage of the power transistor, its power supply drain resistance increases, limiting the current through. In this regard, TI products have a fast response time of approximately 100 ns. Each power tube requires a separate protection mechanism, and it needs to be able to quickly reflect the overcurrent condition without misjudgment. The protection circuit of the discrete device generally only has a total level, and the single power MOSFET is not protected by burning, and it is too late to operate when the second MOSFET is burned.
When TI's motor drive series DRV88xx is completely short-circuited, the loop current can be restored to 9A in about 400, while the output stage is turned off after about 3μs. If it is turned a little slower, 9A means that the motor and the circuit behind it will all burn out.
The integrated protection in the DRV88xx also includes undervoltage lockout, breakdown protection and thermal shutdown. Undervoltage lockout--The chip continuously monitors the supply voltage value. When the voltage is too low, the output is set to a high-impedance state to ensure that the H-bridge can operate normally. Breakdown protection--The high and low sides of the same half-bridge must not be opened at the same time. In order to avoid this phenomenon, a delay (stagnation time) is artificially added between the high-side shutdown and the low-side conduction. The longer the stagnation time, the safer the operation of the H-bridge, but at the same time the linearity and efficiency are worse. Thermal shutdown - excessive heat, insufficient heat sink. Excessive ambient temperatures can cause damage to the chip. The TI chip integrates multiple thermal sensors to continuously monitor the temperature. When the chip temperature rises to the overheat threshold, the H-bridge will be set to high impedance and the micro-stepping subdivision will be reset. Some of TI's products can be pre-judged before thermal shutdown, and the predicted temperature is generally 20 ° C ~ 30 ° C lower than the thermal shutdown threshold.
In terms of technology, TI motor-driven RDSON can achieve 100mΩ or less, while many other manufacturers can only achieve 200mΩ~300mΩ. The lower the internal resistance, the lower the power consumption, and the less likely the leakage is in the sleep state. In addition, the PowerPad has a heat sink on the bottom of the chip, which is directly attached to the PCB. The ground (copper foil) on the back surface is used for heat dissipation, which saves the use of the heat sink.
In terms of algorithms, TI has a Kilby lab in which there are many experts specializing in motors to study processing algorithms. The DRV8818 is very uniform whether it is doing full stepping, 1/2 subdivision, 1/4 subdivision, or doing 1/8 subdivision. In addition, TI's stepper motor drivers have smaller zero-crossing distortion and inductive discharge distortion than comparable products, which means smaller torque ripple and smoother motor operation.
One application of the latest DRV10983 is the exhaust fan for the kitchen. In the past, the kitchen exhaust fan was designed with an AC motor, but the power consumption was high. Nowadays, 24V three-phase sensorless motors are used in the market. First, the cost of the motor has not increased. Second, the energy efficiency control is very good, and the stepless speed regulation can be done. At the same time, it will provide detailed reports, such as whether it is blocked or not, whether the power supply is overvoltage/undervoltage.
Xin Benwei revealed that many fan manufacturers are considering using this solution. Because the country is now demanding energy efficiency ratio, the future exchange and DC will be the development trend of the motor. If the design of the three-phase Hall is troublesome, it is basically the manufacturer to choose a three-phase Hallless design. At the same time, the most basic method of doing three-phase is 120° per phase. This method is not stable and the second is noisy. TI's 180° three-phase sinusoidal control algorithm has an overlap between the phases and phases, which is smooth and can be muted. In addition, the DRV10893 integrates programmable conversion profiles, IPD, Align+Go, forward and reverse start, adjustable communication angle, synchronous rectification, and advanced rotor lock protection (Figure 2).
Figure 2: 24V three-phase sensorless BLDC motor driver DRV10983.
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