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A4979GLPTR-T Datasheet(PDF) 40 Page - Allegro MicroSystems |
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A4979GLPTR-T Datasheet(HTML) 40 Page - Allegro MicroSystems |
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40 / 44 page  Microstepping Programmable Stepper Motor Driver With Stall Detect and Short Circuit Protection A4979 A-6 Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com There are 4 quarter steps for each full step. A full step on the phase diagram is represented by 90°. So each quarter step incre- ments the phase angle by 90° / 4 = 22.5°. In figure A7 the resultant motor current at quarter-step position 8 is one quarter step from the horizontal, so it is at 22.5°. The mag- nitude of the current in phase A at quarter-step position 7, IA7, is therefore sin 22.5°, which is equal to 0.383 or 38.3% of the maximum current. Similarly, the magnitude of the current in phase B at quarter-step position 7, IB7, is therefore cos 22.5°, which is equal to 0.924 or 92.4% of the maximum current. At the 45° positions, 2, 6, 10 and 14, the magnitude of the current in phase A and phase B will be cos 45° = 0.707 or 70.7%, which is the same magnitude as in the half-step case shown in figure A5. Due to symmetry, the phase A current is the same at quarter-step positions 7 and 1. The phase A current at quarter-step positions 9 and 15 also has the same magnitude, but the current is in the opposite direction. In addition the phase B current at quarter- step positions 3, 5, 11, and 13 also have the same magnitude as that of phase A at quarter-step position 7, with a positive current direction for steps 3 and 13 and a negative direction for steps 5 and 11. Similar symmetry can be applied to the phase B current at quarter-step position 7, calculated above. This means that only five discrete current magnitudes are required, including 0% and 100%, in order to drive the stepper motor to all 16 quarter-step positions. Using the same nomencla- ture as figure A7, that is, I Pn , where P is the phase, A or B, and n is the quarter-step number from figure A6, table A1 shows where each of the five magnitude values are used. Figure A8 shows these values plotted as a current sequence diagram. This figure is therefore the time-based equivalent of the phase diagram in figure A6. Table A1. Quarter-Step Phase Current Magnitudes Magnitude (%) Phase B Phase A 0. IA0 –IA8 –– IB4 –IB12 38.3 IA1 IA7 IA9 IA15 IB3 IB5 IB11 IB13 70.7 IA2 IA6 IA10 IA14 IB2 IB6 IB10 IB14 92.4 IA3 IA5 IA11 IA13 IB1 IB7 IB9 IB15 100. –IA4 –IA12 IB0 –IB8 – IB 14 15 0 1 2 3 4 5 6 7 8 9 10 11 12 12 13 IA 38% 70% 92% 100% 0 -38% -70% -92% -100% 38% 70% 92% 100% 0 -38% -70% -92% -100% Figure A8. Phase current sequence for quarter step Figure A9. Measured sixteenth-step phase current sequence |
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