A3955

特点：

• ±1.5A持续电流输出
• 50V额定电压输出
• 内部PWM电流控制
• 3位非先性数模转换器，
• Satlington(TM)能耗驱动器
• 快速、混合和慢速电流衰减模式
• 内部瞬态抑制二极管
• 内部热关断电路
• 交叉电流和UVLO保护

          用来驱动微步运行模式下的双极型步进电机的一个绕组。内部的脉宽调制（PWM）电流控制结合一个内部的非线性数模转换器，使电机的电流可以被控制在全步、半步、四分之一步、八分之一步的模式。非线性增量可使控制线性微步所需的数字量最小化。

  内部电流决定了PWM电流控制电路是工作在慢速（循环）电流衰减，还是快速（再生）电流衰减，或混合电流衰减模式（其关断时间被分为一段快速电流衰减，余下的固定关断时间为慢速电流衰减）。结合可选的电流检测电阻和参考电压，选择输出电流比值的数字量；同时快、慢和混合电流衰减模式给用户提供了一个可变的，较宽的电压控制范围。

  内部保护电路的带滞后时间的热关断保护，瞬态抑制二极管，交叉电流保护。且不需要专门的电源时序。

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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