Understanding DRV8846 Winding Waveform and System Design Input Parameters

Explore the DRV8846 winding waveform and system design input parameters including VM, Vref, Imax, Torque DAC, RL, Rsense, and Ichop calculations. Questions arise regarding waveform stability, current saturation, and appropriate settings for optimal motor performance.

• DRV8846
• Winding Waveform
• System Design
• Torque DAC
• Current Saturation

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1. DRV8846 winding waveform TI Confidential NDA Restrictions TI Confidential NDA Restrictions

2. System design input parameters VM 5 V Rsense RL Vref Imax Torque DAC Full Step peak 3.9 60 3.3 /phase V mA % % mA 128.21 75 70 67.31 Full step 71% winding current A/B Ichop Ichop(A) 0.0683 mA 0.0770 mA (3) (4) VREF*TORQUE DAC*71%/6.6*RISENSE VM/RL+1ohm+Rsense from next slide, use 70% as full step winding current A/B TI Confidential NDA Restrictions 2

3. Ichop=3.3V*0.75*0.70/6.6*3.9=67.3mA VREF*TORQUE DAC*70%/6.6*RISENSE Full step current / phase M0 M1 DEC0 DEC1 TOFF_SEL current L L Z Z Z 6 Full Step (70%)Increase:Mix decay Decrease:Mix decayToff=10us 67.3mA From the beginning of switching to end of switching, dv/dt changes. It this normal behavior? VM 5 V Rsense RL Vref Imax Torque DAC Full Step peak 3.9 60 3.3 /phase V mA % % mA 128.21 75 70 67.31 TI Confidential NDA Restrictions 3

4. Ichop=3.3V*0.875*0.70/6.6*3.9=78.5mA VREF*TORQUE DAC*70%/6.6*RISENSE Full step current / phase M0 M1 DEC0 DEC1 TOFF_SEL current L L Z Z Z 7 Full Step (70%)Increase:Mix decay Decrease:Mix decayToff=10us 78.5mA RL=60 and Rsense=3.9 so VM/Rtotal=5/63.9=78mA. (not include Rdson). 78mA=156mApk-pk so 156mA looks correct but the waveform looks unstable. Is this normal behavior? VM 5 V Rsense RL Vref Imax Torque DAC Full Step peak 3.9 60 3.3 /phase V mA % % mA 128.21 75 70 67.31 TI Confidential NDA Restrictions 4

5. Ichop=3.3V*1.00*0.70/6.6*3.9=89mA VREF*TORQUE DAC*70%/6.6*RISENSE Full step current / phase M0 M1 DEC0 DEC1 TOFF_SEL current L L Z Z Z 8 Full Step (70%)Increase:Mix decay Decrease:Mix decayToff=10us 89mA when Torque DAC=100%, VREF*TORQUE DAC*70%/6.6*RISENSE) > 78mA(VM/RL+Rsense) Is it ok to use this Ichop > 78mA_Imax setting? VM 5 V Rsense RL Vref Imax Torque DAC Full Step peak 3.9 60 3.3 /phase V mA % % mA 128.21 75 70 67.31 TI Confidential NDA Restrictions 5

6. Question Question 1 From the beginning of switching to end of switching, dv/dt changes. It this normal behavior? Question 2 RL=60 and Rsense=3.9 so VM/Rtotal=5/63.9=78mA(not include Rdson). 78mA=156mApk-pk so 156mA looks correct but the waveform looks unstable. Is this normal behavior? Question 3 when Torque DAC=100%, 89mA (VREF*TORQUE DAC*70%/6.6*RISENSE) > 78mA (VM/RL+Rsense). Is it ok to use this Ichop > 78mA_Irmax setting? motor saturation current is higher than 80mA so motor current doesn t saturate in all waveform. TI Confidential NDA Restrictions 6