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C8051F850 Sensorless BLDC Motor Control Reference Design

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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

• 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

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Small motors Remote control helicopters, toy cars Electronic speed controllers (ESC) PC fans Electric fans

Electric tools Cutters, shears, lawn mowers Staplers

Small appliances Mixers and grinders Electric shavers and toothbrushes Vacuum cleaners Condensers and evaporators

Target Applications

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Motor Control Reference Design HardwareMCU Board

Powertrain Board

C8051F850

Gate Drivers

3-Phase Inverter

Power Source Option(Bench Power Supply)

Power Source Option(AC/DC Adaptor)

Turnigy 3800 kV Outrunner Helicopter Motor

Direction

Start/Stop

MCU Reset

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BLDC Motor Control Board Block Diagram

Rx

MTR_VDC

AH

AL

BH

BL

CH

CL

Three-Phase Inverter

J6

MTR_VA

MTR_VB

MTR_VC

M

J5MTR_VDC

12V

5V

3.3V

Regulators+12V

+3.3V

+5V

MCU_GND

VMA

MTR_VA

R23

R27C10

+3.3V

R68

MCU_GND

MTR_VA

MTR_VB

MTR_VC

C14 R34 R36

R33

R31

R35

R32

+3.3V

R73R72 R74

Zero-Crossing Detect Filter Circuit

MTR_VA

MTR_VB

MTR_VC

+3.3V

VMA

VMB

VMC

VMY

IM_0P

Gate Driver

Motor Mount BoardMCRD-MMT-1525

Powertrain Board MCRD-PWR-NLV

C8051F850

VMYVMCVMBVMA

Current sense amplifier

POT

+3.3V

Start/Stop

Direction

FG

UART_RX

UART_TX

UART-USB Bridge

C2 USB Debug

USB Hub

USB Interfaces

UART_TX

UART_RX

USB of PC

+3.3V

MCU Board MCRD-MCU-C8051F850

Sensorless BLDC Motor Control Hardware Block Diagram

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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 availableSilicon Labs Spinner

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Motor Control Reference Design Specifications

Parameter Min Typ Max UnitPower supply 10 24 VMotor driver PWM frequency 24 kHzContinuous average output current 10 ASpeed range (2-pole motor) 200,000 RPMSpeed range (4-pole motor) 100,000 RPMSpeed range (6-pole motor) 66,667 RPM

Motor Specifications - Turnigy 450 Series 3800 kV Brushless OutrunnerParameter Min Typ Max UnitNumber of poles 6Operating voltage range 7.4 14.8 VMaximum current 35 AMaximum power 365 WNo-load full-speed average current @ 12 V 3.66 ANo-load peak startup current @ 12 V 11 AMotor constant 3,800 RPM/VMaximum speed @ 12 V 45,600 RPM

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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

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C8051F85x/6x Motor Control EnhancementsTrue 12-bit ADC

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

Internal precision voltage reference Voltage output 1.65 V ±2% absolute accuracy

Analog comparators Two analog comparators Programmable hysteresis and response time

• High speed @ 100 ns• Low power @ 1.5 µs Comparator ADC Multiplexing

12-bit ADC

ANALOG

MUX

Temperature Sensor

1.65V Internal Reference

VDDExternal Vref

(P0.0)

VDD

P0.0P0.1

P0.7

P1.0P1.1

P1.7

0.5x-1x Gain

ADC Block

12-bit ADC

MUX

MUX

Comparator1

MUXP1.0P1.1

P1.7

+

-

Programmable Hysteresis

ProgrammableResponse Time

0.5x-1x Gain

MUX

MUX

Comparator0+

-

Programmable Hysteresis

ProgrammableResponse Time

P0.1

P0.7

P0.0

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Motor Control Enhancements Cont’d

Flexible comparator multiplexer to support sensorless BEMF commutation

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 signal

CMP output

PWM output

Comparator clear function

3-channel 8- to11-bit or 16-bit PWM

Cycle-by-cycle current control Comparator clear function

(hardware fault protection)

Output polarity select control

Center and edge alignment PWM

PWM with Hardware Fault Protection

Motor Control Multiplexer

12-bit ADC

MUX

MUX

Comparator0

MUXP0.0P0.1P0.7

+

-

Programmable Hysteresis

ProgrammableResponse Time

0.5x-1x Gain

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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

P0.3 = PCA CEX0Operating as

tracking signal

P0MDIN.3 = 1

Output = high before ZCP

Peripheral configuration for zero crossing detection for rising open phase BEMF voltage

+

-

CMP0

VMA

VMY

P0.0 = PCA CEX0Operating as

tracking signal

P0MDIN.0 = 1

Output = high before ZCP Peripheral configuration for zero crossing detection for falling open phase BEMF voltage

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Zero Crossing Detection

CEX1 (motor PWM)

CEX0 (tracking signal) Compa rator active tracking

PCA Cycl e Overflow

Comparator blanking synchronization with low motor PWM duty cycle

CEX1 (motor PWM)

CEX0 (tracking signal) Compa rator active tracking

PCA Cycl e Overflow

Comparator blanking synchronization with high motor PWM duty cycle

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Motor Startup -- Automatic Current Limit

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

Comparator Output (Black)(50% duty cycle)

Comparator Output (Red)(Comparator Clear)

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Hyperdrive Mode

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

0 60 120 180 240 300 360 420 480 540 600 660 720 780

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

Phase C Zero Crossings

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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

Development collateral Schematics BOM Motor control source code www.silabs.com/mcu

C8051F850-BLDC-RD retails for $164.99

Silicon Labs Spinner

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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-to-market Production-ready source code expedites design-

in time Development collateral available at

www.silabs.com/mcu

Get Your BLDC Motor Control Design Up and Spinning

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