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SLA7071M Arkusz danych(PDF) 7 Page - Allegro MicroSystems |
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SLA7071M Arkusz danych(HTML) 7 Page - Allegro MicroSystems |
7 / 12 page SLA7070M, SLA7071M, SLA7072M, and SLA7073M Motor Driver ICs 7 www.allegromicro.com PWM Current Control The description in this section is applicable to the PR and R products. • Blanking time The actual operating waveforms on the SENSEx pins when driving a motor are shown in figure 1. Immediately after PWM turns OFF, ringing (or spike) noise on the SENSEx pins is ob- served for a few μs. Ringing noise can be generated by various causes, such as capacitance between motor coils and inappropri- ate motor wiring. Each pair of outputs is controlled by a fixed off-time (7 to 12 μs, depending on stepping mode) PWM current-control cir- cuit that limits the load current to a desired value, ITRIP. Initially, an output is enabled and current flows through the motor wind- ing and the current-sense resistors. When the voltage across the current-sense resistor equals the DAC output voltage, VTRIP, the current-sense comparator resets the PWM latch. This turns off the driver for the fixed off-time, during which the load induc- tance causes the current to recirculate for the off-time period. Therefore, if the ringing noise on the sense resistor equals and surpasses VTRIP, PWM turns off. To prevent this phenomenon, the blanking time is set to override signals from the current-sense comparator for a certain period right after PWM turns on (figure 2). FUNCTIONAL DESCRIPTION Figure 1. Operating waveforms on the SENSEx pins during PWM chopping Out Out 0 5 μs/Div. 500 ITRIP Expanded Time Scale t Figure 2. SENSEx pins pattern during PWM control tON Blanking Time A A 0 ITRIP tOFF (Fixed) PWM Pulse Width t |
Podobny numer części - SLA7071M |
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Podobny opis - SLA7071M |
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