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Application Brief

High-Efficiency , Code-Free Sensorless BLDC Motor
Drives for Scalable Systems

Code-Free Sensorless Control of BLDC Motors
Development of a sensorless end usable motor
control algorithm for brushless DC (BLDC) or
permanent magnet synchronous motor (PMSM) canbe complex and time consuming. There can bedifferent challenges, including the reliable motor
starting in all scenarios without backspin, on-thefly catch of initial motor spin in either direction,accurate sensing of motor current and voltages for thereliable estimation of motor position. Other challenges
include the variation of motor parameters, controlled
motor stopping, faster acceleration and deceleration,
ultra-high speed, built-in protection against motor
lock, over current and short circuit, and so on.
This process can be difficult and requires longer
development and test time. The MCT8329A code-free
sensorless trapezoidal control three phase gate driverhelps designers accelerate a design, tune motors
for improved performance without writing code, andenables scalable, high efficiency, low-noise, robust
motor control.

efficient ultra-high speed more than 3 kHz (morethan 180 kRPM for a 2-pole motor) motor
electrical frequency. Figure 1 shows more than
3 kHz operation of MCT8329A illustrating proper
commutation giving optimum motor current.
Figure 2 shows initial speed detection at 3 kHz
motor speed and on-the-fly catch to closed loop
commutation.

Figure 1. Motor Speed More Than 3 kHz with
MCT8329A

MCT8329A for a Powerful, Compact, and Highly
Efficient Drive
For applications such as vacuum cleaners andblowers, a high-speed operation can reduce thesize of the system and provides powerful suction orair flow. However, controlling a BLDC motor using
sensorless methods at ultra-high speeds can bechallenging and can result in lower efficiency due toimproper motor commutations.
The MCT8329A device integrates multiple techniques
to achieve improved efficiency across operatingspeeds.
1. Hybrid Commutation Scheme: The MCT8329A
device integrates a hybrid commutation, where
the commutation instant is determined by using
back-EMF integration at low-medium speeds andby using built-in precision comparators (BEMFzero crossing) at higher speeds. The algorithmautomatically transitions between back-EMF
integration and comparator-based commutation
depending on the motor speed. The built-in
comparator based commutation enable high
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Figure 2. On-The-Fly Catch at 3 kHz Initial Speedusing MCT8329A
2. Lead-Lag Control: To achieve optimizedefficiency, the drive state of the motor must be
controlled so that the motor phase current isaligned with the motor BEMF voltage. For motors
with high saliency, a slight advance or delay ofmotor current compared to back EMF can provide
increased torque output and increased efficiency.
The MCT8329A integrates lead-lag angle control(-20o lead and 30o lag) to maximize efficiency andtorque output.

High-Efficiency , Code-Free Sensorless BLDC Motor Drives for Scalable
Systems
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3. Mixed PWM Modulation: The traditional
commutation of BLDC motor uses high sidemodulation where the high side power switch isswitched at PWM frequency at the target duty
cycle for 120 o electrical period. The low side
power switch is kept on continuously for 120oelectrical period. The other approach can be low
side modulation. In either case, there can becurrent in the floating phase winding while theother phases are switching, as shown in Figure 3.
This can reduce the effective torque, and increase
the torque ripple, which results in additional power
loss and can cause unequal distribution of losses
between the high side and low side switches. This
results in reduced torque delivery at lower duty
cycles.

the commutating phase current reaches zero toeliminate false back EMF sensing.
Quiet BLDC Motor Operation
For home, office, or commercial uses, lower noise isa prime requirement in motor drive applications. TheMCT8329A provides advanced sensorless trapezoidal
control techniques with additional 150o modulation
to reduce BLDC motor noise by 2-4% compared toconventional 120o trapezoidal control designs.
Figure 5 shows the phase current for a high speed (1kHz electrical) vacuum cleaner low inductance motorin 150° commutation.

The MCT8329A device integrates a mixed
modulation scheme where the floating phasecurrent can be eliminated as shown in Figure 4,resulting in improved torque, efficiency, and equal
distribution of losses.

Figure 5. High Speed Operation of a Vacuum
Cleaner Motor with 150o Modulation
Scalability to Achieve up to 100% Development
Reuse

Figure 3. High Side PWM Modulation

Figure 4. Mixed PWM Modulation
4. Dynamic Voltage Scaling and Dynamic
Degauss: The MCT8329A device integrates
techniques to improve the accuracy of motor
commutation instant. The dynamic voltage scaling
for back EMF sensing comparators optimizes thevoltage sense resolution across a wide range ofoperating voltage. The dynamic degauss feature(or adjustable degauss window) allows the user
to tune the back EMF sensing window until
2

Development of a single platform across multiple end
applications helps reduce production cost, improve
inventory management, lower design effort andenable faster release to market. The MCT8329A
device enables scalability across voltage, power, andmotor control algorithms.
1. Scalability across voltage: The MCT8329A
driver supports operating voltage from 4.5 V to 60
V that can support single PCB design for different
application voltages such as 5 V, 12 V, 18 V,
24 V, 36 V and so on by scaling the external
MOSFETs and capacitors. The integrated gate
driver architecture of bootstrap with charge pumps
helps to achieve 100 % duty cycle support anda VGS of more than 8 V for external MOSFETs(even at 5-V DC supply voltage) and provides
sufficient gate-to-source voltage for a standard
MOSFET.
2. Scalability across power: The gate drivers in theMCT8329A device can provide up to 1 A sourceand 2 A sink current for the external MOSFETs,
help to drive applications that require power
levels more than 1 kW, and allows the designer
to create a single platform across application

High-Efficiency , Code-Free Sensorless BLDC Motor Drives for Scalable
SystemsCopyright © 2023 Texas Instruments Incorporated

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power levels by changing the on-state resistance(RDS_ON) of the external MOSFET by properly
sizing the sense resistor and the bulk capacitor
and adjusting the gain of integrated current sense
amplifier.
3. Scalability across motor control: The
MCT8329A device integrates 120o and 150o
commutation, configurable PWM switchingfrequencies, and PWM modulation schemes toselect the control as per application need.
Fast Real Time Control System Response
There are many applications that require fastacceleration or deceleration of motor. Applications
such as CPAP machines and automotive fuel pumps
must decelerate and accelerate within few tens ofmilliseconds. A vacuum cleaner must accelerate tofull speed within couple of seconds for improved
user experience. A fast acceleration or deceleration
poses system challenges including a loss of sync
for sensorless motor control, pumping energy backto the DC bus, which increases DC bus voltage thatcan require higher rated capacitor or higher rating ofdownstream devices.
The MCT8329A delivers real-time responses byproviding fast, reliable, and safe operation for fast
start up and acceleration to full speed and fast stop.
With the patented fast deceleration technology in theMCT8329A driver, it is now possible to achieve up to50% faster deceleration than traditional motor control
techniques. The MCT8329A stops the motor without
pumping energy back into the battery, which protects
the motor system from damage. Figure 6 shows thedeceleration of a CPAP motor from 33 kRPM to 3.3
kRPM within 130 ms.
The MCT8329A device integrates reliable fast start
up methods with independently configurable start up
and open loop setting and with automatic open loop toclosed loop hand-off, the user can achieve faster startup time, such as 35 ms start up time from stationary
to full speed (270 Hz) in an automotive fuel pump
application, as shown in Figure 7. Figure 8 shows
acceleration to full speed of 1.2 kHz (72 kRPM) in avacuum cleaner motor within 1.5 seconds using theMCT8329A driver.

Figure 6. Fast Deceleration with a CPAP Motorusing MCT8329A
FGPhase current

Speed

Figure 7. Fast Acceleration with a Fuel Pump
Motor using MCT8329A

Figure 8. Fast Acceleration with a Vacuum Cleaner
Motor using MCT8329A
Conclusion
The MCT8329A driver can help design the next
generation of high speed powerful vacuum cleaners,
garden leaf blowers, or other BLDC applications byenabling a scalable, ultra-high-speed, efficient andfast responding platform design.
References
1. Texas Instruments, MCT8329A High Speed
Sensorless Trapezoidal Control Three-phase
BLDC Gate Driver, data sheet.

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