2. Introducing the BLDC Motor Control Reference Design
Fully featured brushless dc
(BLDC) motor control solution
Demonstrates C8051F85x/6x control
of sensorless BLDC motors
Incorporates motor-driving power
electronics with MOSFETs
Motor control GUI allows real time
motor control and data streaming
Contains everything needed to spin
motor in less than 5 minutes
Reference design benefits
Highlights motor control features of the C8051F85x/6x MCU family
•
•
•
•
•
2
12-bit ADC
Dual comparators
High-speed PWM output
Intelligent comparator operation
Flexible crossbar architecture
Includes production-ready source code that expedites design-in time
Provides a competitive, cost-effective solution
3. Target Applications
Small motors
Remote control helicopters, toy cars
Electronic speed controllers (ESC)
PC fans
Electric fans
Electric tools
Cutters, shears, lawn mowers
Staplers
Small appliances
3
Mixers and grinders
Electric shavers and toothbrushes
Vacuum cleaners
Condensers and evaporators
4. Motor Control Reference Design Hardware
MCU Board
C8051F850
Turnigy 3800 kV Outrunner
Helicopter Motor
Direction
Start/Stop
MCU Reset
Gate Drivers
3-Phase Inverter
Powertrain Board
Power Source Option
(Bench Power Supply)
4
Power Source Option
(AC/DC Adaptor)
5. BLDC Motor Control Board Block Diagram
Regulators
+3.3V
+12V
FG
12V
+5V
5V
J5
MTR_VDC
POT
+3.3V
3.3V
Start/Stop
Direction
J6
C8051F850
UART_TX
UART_RX
MTR_VDC
MTR_VA
Gate Driver
+3.3V
AH
VMA
VMB
VMC
VMY
BH
USB of PC
M
MTR_VC
AL
UART-USB
Bridge
MTR_VB
CH
UART_TX
BL
CL
IM_0P
UART_RX
USB
Hub
Rx
Motor Mount Board
MCRD-MMT-1525
C2 USB
Debug
USB Interfaces
Current sense
amplifier
Three-Phase Inverter
+3.3V
+3.3V
MTR_VA
R68
MCU Board MCRD-MCU-C8051F850
R23
VMA
MTR_VA
VMA
VMB
C10
R27
MTR_VB
VMC
VMY
MCU_GND
MTR_VC
+3.3V
MTR_VA
R31
MTR_VB
R32
MTR_VC
R33
C14
R72
R34
R35
R73
R74
R36
MCU_GND
Zero-Crossing Detect Filter Circuit
Powertrain Board MCRD-PWR-NLV
Sensorless BLDC Motor Control Hardware Block Diagram
5
6. Motor Control Reference Design Software
Production-ready firmware
Spins a 2-pole motor at 200,000 rpm
Expedites design-in time
Motor control GUI (Silicon Labs Spinner) Features
Start/stop motor
Speed control
Direction control
Real time monitoring
• Speed
• PWM Duty Cycle
• Current
Advanced mode available
6
Silicon Labs Spinner
7. Motor Control Reference Design Specifications
Parameter
Power supply
Motor driver PWM frequency
Continuous average output current
Speed range (2-pole motor)
Speed range (4-pole motor)
Speed range (6-pole motor)
Min
Typ
Unit
24
10
Max
V
kHz
A
RPM
RPM
RPM
24
10
200,000
100,000
66,667
Motor Specifications - Turnigy 450 Series 3800 kV Brushless Outrunner
Parameter
Number of poles
Operating voltage range
Maximum current
Maximum power
No-load full-speed average current @ 12 V
No-load peak startup current @ 12 V
Motor constant
Maximum speed @ 12 V
7
Min
Typ
Max
Unit
14.8
35
365
V
A
W
A
A
RPM/V
RPM
6
7.4
3.66
11
3,800
45,600
8. C8051F85x/6x MCUs for Motor Control
Fast, cost-effective 8-bit CPU (25 MIPS)
Designed to support 200,000 RPM for 2-pole BLDC motor
Flexible crossbar
Enables PWM on any of 16 pins
Supports mixed-mode PWM to improve long-term reliability of MOSFETs
• Requires MCU to support PWM output to all six MOSFETs
PWM-synchronized comparator blanking
Automatic synchronization of zero crossing detection with motor PWM
Reduces CPU overhead -- no need to interrupt every PWM cycle for zero
crossing detection
• Enables higher frequency PWM for high-inductance motors
Comparator-clear PWM feature
Enables automatic motor current limit during motor startup
Hyperdrive mode
Technique to increase motor speed beyond rated maximum speed
8
9. C8051F85x/6x Motor Control Enhancements
True 12-bit ADC
1.65V Internal
Reference
Programmable sampling rate and resolution
• 200 ksps @ 12-bit resolution
• 800 ksps @ 10-bit resolution
Up to 16 channels
Programmable gain 0.5x or 1x
Window compare
Temperature sensor
Temperature
Sensor
P0.0
P0.1
P0.7
P1.0
P1.1
A
N
A
L
O
G
0.5x-1x
Gain
12-bit ADC
M
U
X
P1.7
VDD
ADC Block
Programmable
Hysteresis
MUX
+
Comparator0
Internal precision voltage reference
Voltage output 1.65 V
±2% absolute accuracy
External Vref
(P0.0)
VDD
MUX
Programmable
Response Time
P0.0
P0.1
P0.7
P1.0
P1.1
MUX
0.5x-1x
Gain
12-bit ADC
P1.7
Analog comparators
Two analog comparators
Programmable hysteresis and response time
• High speed @ 100 ns
• Low power @ 1.5 µs
9
Programmable
Hysteresis
MUX
+
Comparator1
MUX
Programmable
Response Time
Comparator ADC Multiplexing
10. Motor Control Enhancements Cont’d
Motor Control Multiplexer
Flexible comparator multiplexer to support
sensorless BEMF commutation
P0.0
P0.1
P0.7
MUX
0.5x-1x
Gain
12-bit ADC
Programmable
Hysteresis
MUX
+
Comparator0
MUX
Programmable
Response Time
General mux structure supports multiple
input pins
Each input pin can be routed to (+) or (-)
Comparator inputs are multiplexed with
ADC
Reduces the number of pins needed to
perform sensorless BEMF commutation
PWM with Hardware Fault Protection
3-channel 8- to11-bit or 16-bit PWM
PWM
signal
Cycle-by-cycle current control
Comparator clear function
(hardware fault protection)
CMP
output
Output polarity select control
PWM
output
Center and edge alignment PWM
10
Comparator clear function
11. Zero Crossing Detection -- Comparators
C8051F850 advantage: synchronized PWM comparator blanking
C8051F850 PWM can force a comparator input low
Reduces CPU overhead to detect zero crossing when PWM is active; no need
to interrupt once or many times per PWM cycle
CMP0
VMA
+
VMY
-
Output = high before ZCP
P0.3 = PCA CEX0
Operating as
tracking signal
P0MDIN.3 = 1
Peripheral configuration for
zero crossing detection for
rising open phase BEMF
voltage
CMP0
VMY
+
VMA
-
Output = high before ZCP
P0.0 = PCA CEX0
Operating as
tracking signal
P0MDIN.0 = 1
11
Peripheral configuration for
zero crossing detection for
falling open phase BEMF
voltage
12. Zero Crossing Detection
CEX1 (motor PWM)
CEX0 (tracking signal)
Comparator active tracking
PCA Cycle Overflow
Comparator blanking synchronization with low motor PWM duty cycle
CEX1 (motor PWM)
CEX0 (tracking signal)
Comparator active tracking
PCA Cycle Overflow
Comparator blanking synchronization with high motor PWM duty cycle
12
13. Motor Startup -- Automatic Current Limit
Comparator Output (Red)
(Comparator Clear)
Comparator Output (Black)
(50% duty cycle)
I_meas is op-amp amplified current sensor voltage
Motor PWM signal is automatically switched off by comparator clear
feature of PCA peripheral
Firmware can program PWM duty cycle at a constant 50% and allow
the comparator clear feature to limit the current automatically
Typical solutions require a table of duty cycles tuned for a specific motor
13
14. Hyperdrive Mode
Phase A BEMF waveform
Phase A Commutation
Instants
Phase A Zero Crossings
Phase B BEMF waveform
Phase B Commutation
Instants
Phase B Zero Crossings
Phase C BEMF waveform
Phase C Commutation
Instants
0
60
120
180
240
300
360
420
480
540
600
660
720
780
Phase C Zero Crossings
Open phase (shaded regions) terminal after zero crossing detection
is free
Hyperdrive mode -- energize open phase AFTER zero crossing
detection
Delivers additional torque to increase speed of motor
14
15. Motor Control Reference Design Contents
Contains everything you need to get the motor spinning
in five minutes
Evaluation materials
Data sheets
Motor control hardware
Quick-start guide and user’s guide
Silicon Labs Spinner
C8051F850-BLDC-RD
retails for $164.99
Development collateral
Schematics
BOM
Motor control source code
www.silabs.com/mcu
15
Silicon Labs Spinner
16. Get Your BLDC Motor Control Design Up and Spinning
Fully featured BLDC reference design
Demonstrates C8051F85x/6x MCU control of
sensorless BLDC motors
Includes all hardware required to spin a motor
Motor control GUI allows real-time motor control
and data streaming
Highest performance 8-bit solution for
motor control
200,000 rpm achieved with 2-pole motor
PWM-synchronized comparator blanking
Automatic current limit during motor startup
Incorporates hyperdrive mode to increase speed
Accelerated design for fast time-tomarket
16
Production-ready source code expedites designin time
Development collateral available at
www.silabs.com/mcu
The Sensorless BLDC (Brushless DC) Motor Control Reference Design is a ready to use motor control solution with production-quality hardware and software for quick evaluation and deployment in cost-sensitive applications. The reference design is a vehicle for developers to evaluate and adopt low-cost BLDC Motor Control solutions using the recently launched C8051F85x/6x product family. The C8051F85x/6x has best-in-class analog peripherals:16-channel, 12-bit, 200 ksps or 10-bit, 800 ksps ADC with programmable gain Two analog comparators with programmable hysteresis and response time 3-channel enhanced PWM with 8- to 11-bit or 16-bit resolutionCenter or edge aligned PWMOutput polarity select controlCycle-by-cycle current control for overcurrent or fault detectionComparator clear function
The BLDC motor control reference design targets sensorless brushless DC motor control applications.
The motor control hardware contains an MCU control board, a powertrain board and Turnigy 450 Series 3800 kV brushless outrunner mounted on a motor mount board.The powertrain board contains the gate drivers, power MOSFETs, current sensing resistor as well as resistor dividers to attenuate motor phase voltages so that they can be measured by the MCUThe MCU board contains C8051F850 MCU, buttons to start/stop and change direction of the motor as well as a button to reset the MCU. The PWM output from the MCU is used to drive the gate drivers on the powertrain board. The MCU board also contains an op-amp to amplify the current sensing voltage so that it can be measured by the MCU.
The motor control hardware contains an MCU control board, a powertrain board and Turnigy 450 Series 3800 kV brushless outrunner mounted on a motor mount board.The MCU board consists of the following:C8051F850Motor start/stop, clockwise/anticlockwise direction and MCU reset buttonOne rotary variable resistance potentiometer to control speedOp-amp to amplify and bias the current sense voltageUSB hub to support:C2 USB debug interfaceCP2103 USB-UART bridge operating at 115200 baudThe powertrain board contains:Six IRFH7446 Power MOSFETS for the inverter circuitThree Silicon Labs Si8230 isolated dual drivers50 mohms current sensing resistor rated for 10 WResistor divider to generate attenuated motor voltage supply (VMDC) - allows MCU to determine if motor supply voltage is high enough for safe operationResistor dividers to generate attenuated motor phase voltages with a small positive offset voltage (VMA,VMB, VMC)Resistor network to generate attenuated sum of motor phase voltages with a small positive offset voltage (VMY)
A strong value proposition of the Sensorless Brushless DC Motor Control Reference Design is the supporting environment from tools, development kits, software libraries and collateral. The motor control reference design software allows real time control and monitoring of the motor.Silicon Labs offers differentiation in:Motor control source code available which expedites design-insMotor control GUI PC application (Silicon Labs Spinner) offers users flexibility and ease of use when controlling and understanding the BLDC motor operation
Specifications of the motor control reference design as well as the motor included in the kit.
Advantages of the BLDC Motor Control Reference Design:Achieve 200,000 rpm with Silicon Labs low cost C8051F85x/6x MCU product familyThe C8051F85x/6x MCU architecture features a patented crossbar that enables developers to choose peripherals and pinout placement based on their application needs and layout constraints without worrying about the pre-set limitations and pin conflicts ------ allowing usage of small pinout packages, simplifying PCB routing, minimizing PCB layers and ultimately reducing design time, lowering system cost and most importantly optimal usage of pinsThis design kit implements a technique that takes advantage of some unique features of the C8051F850. The open terminal does not yield any zero crossing information when current flows through that terminal. So, a tracking signal is used to disable a comparator input so that the comparator is effectively not operational when current is flowing in the open terminal. This reduces CPU overhead since there is no need to interrupt PWM cycle for zero crossing detectionThe design kit uses the comparator clear feature to trim the motor PWM duty cycle automatically to ensure that the current does not exceed a predetermined level regardless of the motor load or motor supply voltage.In block commutation driving method, maximum speed is achieved when the motor PWM duty cycle is at 100%. Hyperdrive mode is a technique to further increase this maximum speed. This is done by energizing the open phase after zero crossing has been detected
Best-in-class analog peripherals:16-channel, 12-bit, 200 ksps or 10-bit, 800 ksps ADC with programmable gain Two analog comparators with programmable hysteresis and response time The two comparators share a multiplexer with the ADC which helps in saving valuable pins for GPIO’s.Internal precision voltage reference with an absolute accuracy of ±2%
Motor control comparator multiplexerFlexible comparator multiplexer to support sensorless BEMF commutationThe two comparators share a multiplexer with the ADC which helps in saving valuable pins for GPIO’s. The three motor terminals can be connected to three pins on the chip and the multiplexer inside can be used to route them to the ADC and the comparators. PWM with hardware fault protection3-channel enhanced PWM with 8- to 11-bit or 16-bit resolutionCenter or edge aligned PWMOutput polarity select controlCycle-by-cycle current control for overcurrent or fault detectionComparator clear function (hardware fault protection)
Detecting the back-EMF (BEMF) zero crossing point can be challenging when there is an active PWM signal that interferes with the BEMF signal. Some designs implement a low-pass filter for the terminal signals and the virtual neutral. However, a low-pass filter is not suitable for motors with high commutation frequencies because of the phase shift caused by the filter.This reference design implements a technique that takes advantage of some unique features of the C8051F850. The open terminal does not yield any zero crossing information when current flows through that terminal. So, a tracking signal is used to disable a comparator input so that the comparator is effectively not operational when current is flowing in the open terminal.
Zero crossing point (ZCP) cannot be detected reliably when current is flowing in the open terminal because the voltages are dominated by the forward bias voltage of the body diode of the power MOSFETs. Thus, a tracking signal is used to enable the comparator for use at appropriate times during the PWM cycle.When the motor PWM duty cycle is low (inactive period is much longer than the active period), CEX0 is setup to synchronize with the motor PWM signal to observe the BEMF only at the tail end of the inactive part of the PWM cycle as shown in top figure.When the motor PWM duty cycle is high, CEX0 is setup to observe the BEMF at the tail end of the inactive part ofthe PWM cycle and the entire active part of the PWM cycle as shown in the lower figure.
In the typical BLDC motor sensorless starting phase, the motor is driven like a stepper motor. The motor is initially commutated very slowly then velocity is increased while the PWM duty cycle is increased to boost the applied motor voltage in an attempt to keep the current constant.However, it is not easy to predetermine PWM duty cycle for constant current level because the motor load may change or the motor supply voltage fluctuates. The design kit uses the comparator clear feature to trim the motor PWM duty cycle automatically to ensure that the current does not exceed a predetermined level regardless of the motor load or motor supply voltage.Using the comparator clear mechanism, the PWM signal is automatically shut off for that cycle when the current sensing voltage exceeds 1.8 V. The firmware programs the MCU to generate a 50% duty cycle PWM signal for motor startup and lets the comparator clear functionality trim the duty cycle to limit the peak current.
Hyperdrive Mode:In the block commutation driving method, maximum speed is achieved when the motor PWM duty cycle is at 100%.Hyperdrive mode is a technique to further increase this maximum speed. In the typical block commutation, there is zero current through one motor terminal at any one time because thephase is open for ZCP detection. If the open terminal can be energized, there will be increased electrical torquegenerated to further increase the speed of the motor, but the open terminal is required for ZCP detection. However,the open phase is free to be energized after ZCP has been detected. This technique is the most beneficial formotor designs in which the motor current saturates well before the next commutation event.
A strong value proposition of the Sensorless Brushless DC Motor Control Reference Design is the supporting environment from tools, development kits, software libraries and collateral. The motor control reference design contains everything needed to get the motor spinning in under five minutes.Silicon Labs offers differentiation in:Low cost reference design for evaluation purposesMotor control source code available which expedites design-insMotor control GUI PC application (Silicon Labs Spinner) offers users flexibility and ease of use when controlling and understanding the BLDC motor operationCollateral including application notes and knowledge base articles
The Sensorless BLDC (Brushless DC) Motor Control reference design is a ready to use motor control solution with production-quality hardware and software for quick evaluation and deployment in cost-sensitive applications. The reference design is a vehicle for developers to evaluate and adopt low-cost BLDC motor control solutions using the recently launched C8051F85x/6x product family.