Feature: Automotive
also needs to be a 3-phase power stage that can drive the three phases of the BLDC motor to make it spin.
The motor driver Allegro MicroSystems’s A4964KJPTR-T chip is a dedicated BLDC motor driver that contains all the functions needed to drive a motor; see Figure 4. Specifi cally designed for automotive applications and for use with N-channel MOSFETs, the chip has sensorless start-up and commutation, so it requires minimal external hardware. It also operates over a wide range of voltages (5V5-50V), which covers nearly every standard application, including automotive systems. Perhaps its most interesting feature
Figure 1: The Trinamic QBL4208-41-04-006 is a 24V, 4000rpm BLDC motor that can deliver a little over 0.06Nm of torque at maximum speed
Figure 2: The Trinamic QBL4208-41-04-025 is a 24V, 4000rpm BLDC motor but delivers a little over 0.25Nm of torque
but a microcontroller designed for motor control, like the Texas Instruments F280049CRSHSR, will have the algorithms built into the library residing in its ROM. Hence, the only additional code for the application are function calls to access the library, which then does all the heavy liſt ing.
Spinning a BLDC motor doesn’t just
come down to the soſt ware, it also requires hardware. Figure 3 shows an example application using a C2000 microcontroller – of which the F280049CRSHSR is a family member, illustrating everything required or optional to drive a BLDC motor. Beyond a microcontroller, there
is that it can be interfaced to a micro- controller or central electronic control unit (ECU) over a serial peripheral interface (SPI) to confi gure the various registers for motor operation. Obviously, the microcontroller needs not be as powerful as one running the motor control algorithms themselves. Alternatively, the A4964KJPTR-T can also be driven without SPI, simply by providing a pulse width modulation (PWM) signal. T ere is non- volatile memory where the motor settings can be stored, which are loaded at power- on, allowing just a PWM signal to control the motor. From a confi guration perspective, the A4964KJPTR-T has 32 addressable 16-bit registers, plus a status register. T e status register is unique in that the fi rst fi ve bits are transmitted during every read/write operation on the SPI, allowing the soſt ware to check status, to see if there are any faults or issues. All of the status registers can be read out during write operations to the chip since no data is being transmitted back from the A4964KJPTR-T. In the 32 addressable registers, there
are also two special registers: register 30 is write-only and register 31 is read-only. T e write-only register allows a developer to set the demand input and the duty cycle rate the motor will be driven at, with a value 0-1023. T e read-only register data changes based on the requested data written to register 29 – the readback select register. T is register allows a wide range
www.electronicsworld.co.uk April 2022 19
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