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A3952SW Datasheet(PDF) 9 Page - Allegro MicroSystems |
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A3952SW Datasheet(HTML) 9 Page - Allegro MicroSystems |
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9 / 16 page  3952 FULL-BRIDGE PWM MOTOR DRIVER This also improves the maximum rate at which the load current can increase (as compared to fast decay) due to the slow rate of decay during t off. When the average load current is decreasing, fast-decay mode is used to regulate the load current to the desired level. This prevents tailing of the current profile caused by the back-EMF voltage of the stepper motor. In stepper motor applications applying a constant current to the load, slow-decay mode PWM is used typically to limit the switching losses in the device and iron losses in the motor. DC Motor Applications In closed-loop systems, the speed of a dc motor can be controlled by PWM of the PHASE or ENABLE inputs, or by varying the REF input voltage (V REF). In digital systems (microprocessor controlled), PWM of the PHASE or ENABLE input is used typically thus avoiding the need to generate a variable analog voltage reference. In this case, a dc voltage on the REF input is used typically to limit the maximum load current. In dc servo applications that require accurate position- ing at low or zero speed, PWM of the PHASE input is selected typically. This simplifies the servo-control loop because the transfer function between the duty cycle on the PHASE input and the average voltage applied to the PCB Layout The load supply terminal, V BB, should be decoupled (>47 µF electrolytic and 0.1 µF ceramic capacitors are recommended) as close to the device as is physically practical. To minimize the effect of system ground I•R drops on the logic and reference input signals, the system ground should have a low-resistance return to the load supply voltage. See also “Current Sensing” and “Thermal Consider- ations” above. Fixed Off-Time Selection With increasing values of t off, switching losses de- crease, low-level load-current regulation improves, EMI is reduced, the PWM frequency will decrease, and ripple current will increase. The value of t off can be chosen for optimization of these parameters. For applications where audible noise is a concern, typical values of t off are chosen to be in the range of 15 to 35 µs. Stepper Motor Applications The MODE terminal can be used to optimize the performance of the device in microstepping/sinusoidal stepper motor drive applications. When the average load current is increasing, slow-decay mode is used to limit the switching losses in the device and iron losses in the motor. Typical Bipolar Stepper Motor Application + V BB V CC VBB LOGIC VCC VBB LOGIC Dwg. EP-048 MODE 2 ENABLE 2 PHASE2 V REF2 MODE 1 ENABLE 1 PHASE1 V REF1 47 µF +5 V 0.5 Ω 25 k Ω 820 pF |
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