Innocent Irakoze Dalton Ortega. Date: Nov 19 th, 2018

Transcription

1 Part 3: What is smart gate drive and what does it mean for me? Smart Gate Drive and its benefits Stepper smart tune and its benefits Sine (180 ) commutation Current sensing and current regulation Innocent Irakoze Dalton Ortega Date: Nov 19 th, 2018

2 Smart gate drive Space saving Protection Easytouse Gate Driver Scalable/Higher Currents High Control Flexibility Control DRVx Gate Driver Feedback Protection Reduced Board Space Full Protection FETs Texas Instruments Motor Drives

3 Examining the motor drive system Competitor gate driver V GATE V BST Smart Gate Driver V DS Monitor OC Detect R SOURCE V SUPPLY V SUPPLY INH Discrete solution C BST R SINK D SINK R PD To Load V GATE V DS Monitor OC Detect R SOURCE INL R SINK D SINK R PD TI Information Selective Disclosure

4 Smart gate drive technology benefits Smart Gate Driver Gate drive strength adjustability dv/dt protection, strong pull down Gate drive fault protection Closedloop dead time Passive gate pulldown (efficiency) (flexibility) (robustness) (cost and size) Gate Drive (Internal) MOSFET (External) V GATE V GATE V GATE V GATE V GATE V GATE Source 10 ma 20 ma 50 ma OFF ON OFF OFF 110 ma OFF 250 ma OFF 560 ma I SOURCE Sink 20 ma 40 ma 100 ma OFF OFF OFF OFF 220 ma OFF 500 ma OFF 1120 ma Switch 1 Switch 2 Switch N TI Information Selective Disclosure

5 Smart gate drive technology benefits Smart Gate Driver Gate drive strength adjustability dv/dt protection, strong pull down Smart fault response Closedloop dead time Passive gate pulldown I DRIVE for t DRIVE Gate Drive Setting, I DRIVE TI Information Selective Disclosure

6 Smart gate drive technology benefits Smart Gate Driver Gate drive strength adjustability dv/dt protection, strong pull down Smart fault response Closedloop dead time Passive gate pulldown DRV832x, DRV98323 SPI Settings SPI Settings Hardware Settings DRV832x Hardware Settings Persistence capture of slew rate with different gate drive settings TI Information Selective Disclosure

7 Smart gate drive technology benefits Smart Gate Driver Gate drive strength adjustability dv/dt protection, strong pull down Smart fault response Closedloop dead time Passive gate pulldown DRV832x, DRV98323 SPI Settings SPI Settings Hardware Settings DRV832x Hardware Settings DRV832x & DRV835x: Family of 60V/100V three phase smart gate driver with buck regulator and three current shunt amplifiers Key applications that benefit from smart gate drive Power Tools TIDA01516 BrushlessDC Motor Drives TIDA01619 Electric Bikes and Scooters TIDA00774 Electronic Speed Control (ESC) TIDA00643 TI Information Selective Disclosure

8 Smart gate drive technology benefits Smart Gate Driver Gate drive strength adjustability dv/dt protection, strong pull down Gate drive fault protection Closedloop dead time Passive gate pulldown Smart Gate Driver Implementation of Miller Clamp OFF > ON V SUPPLY Strong Pull Down I SOURCE C GD Coupling C GD V DS V GS I STRONG TI Information Selective Disclosure

9 Smart gate drive technology benefits Smart Gate Driver Gate drive strength adjustability dv/dt protection, strong pull down Gate drive fault protection Closedloop dead time Passive gate pulldown VCP HS VGLS LS Smart Gate Driver Gate Monitor Gate Monitor GHA SHA GLA Continuous gate monitor: Intelligently detect a FET gate short Protects against low gate drive settings Prevents shoot through during faults I HOLD to protect gates after switching TI Information Selective Disclosure

10 Smart gate drive technology benefits Smart Gate Driver Gate drive strength adjustability dv/dt protection, strong pull down Gate drive fault protection Closedloop dead time Passive gate pulldown Traditional: Dead time on the input Smart Gate Drive: Dead time on the output INH INL t DEAD INH INL t DEAD GH GH GL GL SH SH TI Information Selective Disclosure

11 Smart gate drive technology benefits Smart Gate Driver Gate drive strength adjustability dv/dt protection, strong pull down Gate drive fault protection Closedloop dead time Passive gate pulldown Traditional: Use external passives to keep the FETs off Smart Gate Drive: Integrated pulldown resistor in sleep mode or power off GHA GHA SHA SHA GLA GLA TI Information Selective Disclosure

12 Smart tune Automatic decay mode for stepper motors Texas Instruments Motor Drives

13 Why do decay modes matter in stepper motors? Keeping current in regulation ensures that the motor operates smoothly, quietly, and efficiently. Engineers traditionally spend weeks to months tuning stepper motor drivers to chose the best decay mode over their operating conditions The best decay mode will depend on several factors: Supply voltage Motor resistance and inductance Motor rotation speed (BackEMF) Inductor saturation

14 Regulate current with decay modes Fixed mixed decay Begins as fast decay After TDECAY, switches to slow decay I (A) xout1 Slow Fast Driving decay xout2 ITRIP t (us)

15 Optimizing stepper performance Current distortion At high speed, motor BEMF operates differently in quadrants I and II Slow speed Fast speed I II I II Microstepping angle ( ) Quadrant I: BEMF is out of phase with the current Quadrant II: BEMF is in phase with the current Microstepping angle ( ) May only need slow decay at speed Need a more aggressive decay at speed

16 Smart tune in action Fixed 30% mixed decay Slow speed (3 khz) Fast speed (10 khz) Loss of current regulation Smart tune applied TI Information Selective Disclosure

17 How smart tune technology works Optimize decay mode iteratively for a given current step: cyclebycycle changes on the decay mode if needed Overshoot needs to be more aggressive (prevents regulation loss) Long drive time needs to be less aggressive (operates more efficiently) TI Information Selective Disclosure

18 2 µs Mixed Decay Smart tune Smart tune Smart tune Case Temperature ( C) 2 µs Mixed Decay Smart tune Smart tune in action V 40 V 11 C 12 C 2 µs fixed mixed decay versus smart tune 8 C 40 V 6 C 5 C 24 V 24 V 7 C 40 V µs 20 µs 30 µs Off time TOFF (µs) Smart tune runs 512 degrees cooler at load!

19 Smart tune technology for stepper motors Available on DRV8846, DRV8880, DRV8881E, and DRV8886AT. More to come! DRV8846: 12V 3D printer reference design DRV8881: Stage lighting tilt/pan reference design DRV8886AT: 24V, 2A Stepper driver evaluation module w/ smart tune These drivers automatically configure the decay mode onthefly to operate at the best setting for motor operation Key benefits of smart tune technology: Don t need to spend weeks/months tuning the motor (development cost) Motor runs more efficiently than fixed decay modes (power budget) Motor runs quietly without losing regulation (performance) Adjusts to motor parameter changes over lifetime (reliability) You can source multiple motor vendors (production risk management)

20 BLDC motor commutation Texas Instruments: BLDC Motor Drivers TI Information Selective Disclosure

21 BLDC commutation I I A B N C S C N S I I B A

22 BLDC motor operation on off Vm V Iin 1 N S N S CenterTap 3 6 Vm off U off Vm Iout off W on 6 different commutation cycle (electrical cycle) to move rotor between 2 poles. (rotor position relative to stator is exactly same for every poles away) For 4 poles motor, commutation controller needs goes through 2 electrical period for one mechanical revolution. o 1 mechanical revolution = 2 electrical cycles o 2 electrical cycles = 12 commutation states

23 Electrical cycle and mechanical cycle S Mechanical cycle: Time for the motor to travel One full revolution Mechanical angle corresponding to the Mechanical cycle. Electrical cycle: Time for the rotor to pass a pair of Poles. Electrical angle corresponding to the Electrical cycle. N N S

24 Speed vs torque Current is directly proportional to Torque When torque increases, so does the current. As a result: Voltage drop on the motor resistor increases Speed decreases because VBEMF = VSVRLdi/dt Vs R L M BEMF Motor rotation creates the BEMF. Higher the speed of motor higher is amplitude of generated BEMF. This generated BEMF offsets the applied the voltage

25 Trapezoidal commutation v/s sinusoidal commutation Phase A Phase B Phase C Step Trapezoidal Control: 2x Phases always on / 1x Phase off Easy control and requires less processing power Torque ripple is higher Sinsusoidal with third harmonics Control can be complicated and requires more processing power Less torque ripple Higher efficiency

26 Performance: Driving methods vs. acoustics 120 phase current 150 phase current 180 phase current sinusoidal Various drive methods are available Pure tone acoustics are significantly reduced when using sinusoidal drive

27 Sinusoidal commutation N S N S How could the control system know, the rotor position? Two ways to determine rotor position: Sensors Estimation (sensorless)

28 Motor position and speed sensors Resolver High resolution, AD input. High cost Optical Encoder High resolution Calculation Low reliability Hall Effect Low resolution Low cost Sin Cos A B Z U V W Rotor angular position

29 How does hall sensor work? 1 N S Hall sensor output Hall sensor Halleffect sensor outputs the 01 signal indicating the Polarity of Magnetic Field going throw its surface. Halleffect sensor should be installed at specific location. One Halleffect sensor can distinguish the Cycle into Two parts. 0

30 Commutation sine drive 180 sine commutation (DIR = 0) State Hall U Hall V Hall W Phase U HS Phase U LS (1) (1) Phase V HS Phase V LS (1) (1) (1) Phase W HS Phase W LS (1) (1) (1) (1) Low for asynch rectification, inverted HS signal for sync rectification

31 Positionestimation backemf EMF: Electromotive Force, the origin of voltage in electrical devices. Faraday's law: The EMF generated when a wire moves across magnetic field. N S

32 Positionestimation backemf When a motor spins, the Permanent Magnetic rotor, moving across the stator coils induces a voltage (Back EMF) BEMF Magnetic Flux * Speed. Position = Function( Magnetic Flux) N S Induced Voltage sin(theta)

33 Positionestimation backemf Motor Model U R I L M BEMF BEMF can be estimated using motor parameters, voltage and current information U is applied voltage to motor phase. For any given system current is measured using shunt or current sensor. R is motor resistance V BEMF = U I R L di dt L is motor inductance

34 Sensored control v/s Sensorless control Motor commutation based on feedback from Resolver/Encoder/Hall sensors Motor commutation based on either estimated/measured BEMF Motor can quickly respond to load changes Low speed of operation easier to control No backward rotation necessary to find initial position of motor Least amount of board space used since no Hall sensors needed Easier to connect control circuitry to motor Most cost effective, compact solution

35 Speed command: Analog, Digital and PWM There are different ways in which the control signals for changing speed of the motor is applied : Pulse Width Modulated signal (PWM) Variable DC voltage (Analog) I2C communication (Digital) Control Signal (PWM, I2C or Analog) Speed command Output PWM (Command * VCC) Based on calculated PWM, the output of driver is adjusted 35

36 Integrated current sensing technology Texas Instruments: BrushedDC and Stepper Motor Drivers TI Information Selective Disclosure

37 Why do I need to sense the current? BrushedDC Motor Stepper Motor Inrush Current Limiting Torque Control Stepping and Microstepping Current Regulation and Current Control TI Information Selective Disclosure

38 Current sensing resistor BrushedDC 10 µf 0.1 µf OUT1 10 µf 0.1 µf OUT1 IN1 IN2 PWM Logic Gate Drive and Charge Pump OUT2 BDC IN1 IN2 PWM Logic Gate Drive and Charge Pump OUT2 BDC VREF 1/Av ISEN RISEN ILIM Current Sensing RILIM GND PPAD 1206 or larger GND 0402 or smaller PPAD PGND DRV8870: 3.6A BrushedDC driver, traditional current sensing DRV8876: 37V, 3.6A BrushedDC driver with integrated current sensing and current sense output

39 Current sensing resistor stepper 0.1 µf 0.1 µf bulk 0.01 µf 0.01 µf bulk 0.47 µf 10 ma 0.1 µf 0.47 µf VCP CPH CPL V3P3 STEP DIR ENABLE nsleep ATE TRQ[1:0] M[1:0] DECAY[1:0] TOFF VREF nfault V3P3 V3P3 V3P3 Power Charge Pump 3.3V LDO Control Inputs Analog Input Output AutoTune Core Logic Indexer Protection Overcurrent Undervoltage Thermal 4 4 VREF SINE DAC TRQ[1:0] 1/Av Offtime Gate Drive PWM VREF Offtime Gate Drive PWM SINE DAC TRQ[1:0] 1/Av AOUT1 AOUT2 AISEN RSENSE BOUT1 BOUT2 BISEN RSENSE Step Motor 1206 or larger 0402 or smaller 0.22 µf VCP CPH µf CPL AVDD 0.47 µf 1 ma DVDD 0.47 µf STEP DIR ENABLE nsleep M[1:0] DECAY TRQ RREF RREF nfault DVDD DVDD DVDD DVDD IREF Power Charge Pump 5.0V LDO 3.3V LDO Control Inputs Analog Input Output Adaptive Blanking Core Logic Protection Overcurrent Undervoltage Thermal Microstepping Indexer up to 1/16 Offtime PWM Offtime PWM Gate Drive Gate Drive Gate Drive Gate Drive AIREF IREF AIREF 4 AIREF SINE DAC BIREF IREF BIREF 4 BIREF SINE DAC AOUT1 AOUT2 PGND BOUT1 BOUT2 PGND Step Motor GND GND PPAD GND PPAD DRV8880: 2A Stepper driver with smart tune, traditional current sensing DRV8886AT: 2A Stepper driver with smart tune and integrated current sensing

40 Current sensing resistor stepper 0.1 µf 0.1 µf bulk 0.01 µf 0.01 µf bulk 0.47 µf 10 ma 0.1 µf 0.47 µf VCP CPH CPL V3P3 STEP DIR ENABLE nsleep ATE TRQ[1:0] M[1:0] DECAY[1:0] TOFF VREF nfault V3P3 V3P3 V3P3 Power Charge Pump 3.3V LDO Control Inputs Analog Input Output AutoTune Core Logic Indexer Protection Overcurrent Undervoltage Thermal 4 4 VREF SINE DAC TRQ[1:0] 1/Av Offtime Gate Drive PWM VREF Offtime Gate Drive PWM SINE DAC TRQ[1:0] 1/Av AOUT1 AOUT2 AISEN RSENSE BOUT1 BOUT2 BISEN RSENSE Step Motor 1206 or larger 0402 or smaller 0.22 µf VCP CPH µf CPL AVDD 0.47 µf 1 ma DVDD 0.47 µf STEP DIR ENABLE nsleep M[1:0] DECAY TRQ RREF RREF nfault DVDD DVDD DVDD DVDD IREF Power Charge Pump 5.0V LDO 3.3V LDO Control Inputs Analog Input Output Adaptive Blanking Core Logic Protection Overcurrent Undervoltage Thermal Microstepping Indexer up to 1/16 Offtime PWM Offtime PWM Gate Drive Gate Drive Gate Drive Gate Drive AIREF IREF AIREF 4 AIREF SINE DAC BIREF IREF BIREF 4 BIREF SINE DAC AOUT1 AOUT2 PGND BOUT1 BOUT2 PGND Step Motor GND GND PPAD GND PPAD DRV10970: 3phase sensored BLDC driver with single/3 Hall support and integrated current sensing

41 DRV888x current sense accuracy Traditional Stepper: ±8% DRV888x family: ±6.25% 24 V 24 V LDO LDO ±2% Driver DRV8X STEP STEP DIR DIR MCU VREF Divider ±5% VREF ±1% MCU ±6.25% RREF Already includes ±1% from RREF Resistor <±1% ±1% TI Information Selective Disclosure

42 Integrated current sensing technology Available on DRV8871, DRV8876 (BrushedDC) and DRV8884/5/6/6AT (Stepper) Eliminates all current sense resistors while providing accurate current regulation Key Benefits from integrated current sensing: Removed sense resistors and reduced board size (system cost) No power loss over the sense resistor (power budget) Fewer components on the board (manufacturability) Easy device layout with no sense routing (development) To find out more visit

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