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Related Links:

Datasheets:
A3955: Full-Bridge PWM Microstepping Motor Driver (PDF)

Selection Guides:
Power Integrated Circuits,

Power Motor Drivers,

Power Motor Drivers - Full-Bridge

when this product is updated

Technical Publications:
Monolithic, Programmable, Full-Bridge Motor Driver Integrates PWM Current Control and Mixed-Mode Microstepping  (PDF),

Smart, Constant-Torque, Microstepping Drive Circuitry for Under $10 (PDF)

FAQs:
3955: Full-Bridge PWM Microstepping Motor Driver FAQ

Press Releases:
Full-Bridge PWM Microstepper for Digital Control of Bipolar Stepper Motors

A3955
Full-Bridge PWM Microstepping Motor Driver

Features

• ±1.5 A continuous output current
• 50 V output voltage rating
• Internal PWM current control
• 3-bit nonlinear DAC
• Fast, mixed fast/slow, and slow current-decay modes
• Internal transient-suppression diodes
• Internal thermal shutdown circuitry
• Crossover-current and UVLO protection

Description

The A3955 is designed to drive one winding of a bipolar stepper motor in a microstepping mode. The outputs are rated for continuous output currents to ±1.5 A and operating voltages to 50 V. Internal pulse width modulated (PWM) current control combined with an internal three-bit nonlinear digitalto- analog converter allows the motor current to be controlled in full-, half-, quarter-, or eighth-step (microstepping) modes. Nonlinear increments minimize the number of control lines necessary for microstepping. Microstepping provides increased step resolution, and reduces torque variations and resonance problems at low speed.

Internal circuitry determines whether the PWM current-control circuitry operates in a slow (recirculating) current-decay mode, fast (regenerative) current-decay mode, or in a mixed current-decay mode in which the off-time is divided into a period of fast current decay and with the remainder of the fixed off-time spent in slow current decay. The combination of user-selectable current-sensing resistor and reference voltage, digitally selected output current ratio; and slow, fast, or mixed current-decay modes provides users with a broad, variable range of motor control.

Internal circuit protection includes thermal shutdown with hysteresis, transient-suppression diodes, and crossover-current protection. Special power-up sequencing is not required.

The A3955 is supplied in a choice of two power packages; a 16-pin dual-in-line plastic package with copper heat-sink tabs (suffix ‘B’), and a 16-lead plastic SOIC with internally fused pins (suffix ‘LB’). For both package styles, the thermally enhanced pins are at ground potential and need no electrical isolation. Both packages are lead (Pb) free, with leadframe plating 100% matte tin.

Functional Block Diagram

Complete Part Numbers

Part Number	Package Type	RoHS Compliant	Part Composition/ RoHS Data	Temperature	Comments	Samples	Distributor Stock
A3955SB-T	16-pin DIP	Yes	view data	-20 °C to  85 °C		Contact Local Sales Representative
A3955SLB-T	16-lead SOIC	Yes	view data	-20 °C to  85 °C		Contact Local Sales Representative
A3955SLBTR-T	16-lead SOIC	Yes	view data	-20 °C to  85 °C		Contact Local Sales Representative

Allegro's products are not to be used in life support devices or systems, if a failure of an Allegro product can reasonably be expected to cause the failure of that life support device or system, or to affect the safety or effectiveness of that device or system.