Monolithic Power Systems, Inc. · NASDAQ:MPWR
Monolithic Power Systems — Technical Presentation (June 2022)
28 slides from Monolithic Power Systems's technical presentation, June 2022
Slide 1: Stepper Motors and Back EMF
Stepper Motors and Back EMF Pete Millett Staff Technical Marketing Engineer June 2022
Slide 2: Pete Millett – Staff Technical Marketing Engineer
Pete Millett – Staff Technical Marketing Engineer 2014–Present • MPS Staff Technical Marketing Engineer for motor driver ICs • Responsible for new product definitions as well as application engineering 2005–2013 • Systems Engineer and Systems Manager at Texas Instruments • Product definition and sys
Slide 3: Stepper Motor Back EMF
Stepper Motor Back EMF What is back EMF? Back EMF in a stepper motor Using back EMF for diagnostics Summary / Q&A
Slide 4: What is Back EMF?
What is Back EMF? Brushed DC Motor Brushless DC Motor Stepper Motor Image by Florida State University, micro.magnet.fsu.edu
Slide 5: Stepper Motor Construction
Stepper Motor Construction Images from www.allaboutcircuits.com Permanent Magnet Stepper Motor Hybrid Stepper Motor
Slide 6: Back EMF in the Stepper Motor
Back EMF in the Stepper Motor
Slide 7: Driving a Stepper Motor
Driving a Stepper Motor Winding current can be modulated so it approaches sine and cosine waveforms.
Slide 8: Effect of BEMF on Winding Current
Effect of BEMF on Winding Current Series Inductance LS Power Source Series Resistance VSRC RS V = L*dI/dt Back EMF VBEMF
Slide 9: Effect of BEMF on Winding Current: Low Voltage
Effect of BEMF on Winding Current Low Voltage Rotor Speed Yellow: Voltage Green: Current
Slide 10: Effect of BEMF on Winding Current: High Step Rate
Effect of BEMF on Winding Current High Step Rate Yellow: Voltage Green: Current
Slide 11: Effect of BEMF on Winding Current: Rotor Stalled
Effect of BEMF on Winding Current Rotor Stalled Yellow: Voltage Green: Current
Slide 12: Constant Current Drive
Constant Current Drive Yellow: Voltage Green: Current
Slide 13: Effect of Supply Voltage on Constant Current: High Voltage
Effect of Supply Voltage on Constant Current High Voltage
Slide 14: Effect of Supply Voltage on Constant Current: Low Voltage
Effect of Supply Voltage on Constant Current Low Voltage
Slide 15: Constant Current & BEMF
Constant Current & BEMF 100% Duty Cycle Yellow: Voltage Green: Current
Slide 16: Constant Current & BEMF
Constant Current & BEMF 100% Duty Cycle Yellow: Voltage Green: Current
Slide 17: Using Back EMF Information
Using Back EMF Information Back EMF vs. Speed 50 45 40 Winding Voltage (V RMS) 35 30 25 20 15 10 5 0 0 100 200 300 400 500 600 700 800 900 Electrical Speed (Hz)
Slide 18: Measuring the Back EMF
Measuring the Back EMF
Slide 19: Back EMF Measurements vs. Rotor Speed
Back EMF Measurements vs. Rotor Speed 400 PPS 600 PPS 800 PPS
Slide 20: How to Measure BEMF?
How to Measure BEMF? VIN VIN MP6602 VCP VIN Gate VCC Drive Reg VCC Internal Supplies VG GND & Ref. AOUT1 Gate nFAULT Driver AOUT2 nRESET STEP PGND DIR ENBL Curr. ISENSE SLEEP Reg. µC nSCS BEMF SCLK SPI A/D SDATI I/F VIN SDATO Control BOUT1 Logic Motor OSC Gate BOUT2 Driver PGND UVLO OVP OTS Curr. IS
Slide 21: Stall Detection
Stall Detection 3.6V 0V Rotating Stalled Back EMF = 3.6V Back EMF = 0
Slide 22: MP6602 Stall Detection
MP6602 Stall Detection STD0 STD1 STD2 STD3 STH0 STH1 STP0 STH2 STP1 STH3 STP2 STH4 Auto hold STP3 STH5 STP4 STH6 ENBL STP5 STH7 TSTP STALL nZCS (Zero CLR Current Step) =0 Decode S ADC H done B B Avg A 4 A A=B STALL AOUT1 S&H ADC A<B U/D D 16 AOUT2 8 Stall counter 5V Ref BOUT1 BOUT2 BE0 BES0 BES1 BE1
Slide 23: Low Step Rates
.0ms 20MSis (ems tacgs
Slide 24: Load Torque Estimation
Load Torque Estimation Unloaded Loaded Magenta: Voltage Yellow: Current
Slide 25: Load Torque Estimation via BEMF Measurement
Load Torque Estimation via BEMF Measurement No Torque Moderate Torque Near Stall
Slide 26: Load Torque vs. BEMF
Load Torque vs. BEMF 300 200 180 250 160 Back EMF Measurement Back EMF Measurement 200 140 AVG 120 AVG 150 MIN 100 MIN MAX 80 MAX 100 60 50 40 20 0 0 0 2 4 Torque 6 8 10 0 0.5 1 1.5Torque 2 2.5 3 3.5
Slide 27: Summary
Summary • Stepper motors have back EMF, like any permanent magnet motor • Back EMF effects the winding current, and the ability to step the motor at high speed • Back EMF measurement can be used to provide stall detection, and in some cases provide diagnostic information
Slide 28: Q&A
Q&A Please submit questions through the “Q&A” menu option in the Zoom app This webinar and others will be available for on-demand streaming at: MonolithicPower.com/webinars
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