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High-Performance Power ICs and Hall-Effect Sensors
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Datasheets:
A3955: Full-Bridge PWM Microstepping Motor Driver (PDF)
Selection Guides:
Power Integrated Circuits,
Power Motor Drivers,
Power Motor Drivers - Full-Bridge
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
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FAQs - A3955 Single Full-Bridge PWM Motor Driver 
Q1: Can I microstep with the A3955?
Q2: Is the A3955 available in surface-mount and through-hole packages?
Q3: Removed.
Q4: What is the maximum allowable motor supply voltage and current?
Q5: Can the A3955 drive a stepper motor?
Q6: What protection features come with the A3955?
Q7: Do I need any external components?
Q8: Are there layout concerns that I should be aware of?
Q9: Is this a constant-current or constant-voltage controlled device?
Q10: How can I increase the current in the winding and not exceed the power rating of the package?
Q11: Has a technical paper been written for the A3955?
Q1: Can I microstep with the A3955?
Yes. Due to an internal 3-bit DAC, motor current can be controlled in full, half, quarter, or 1/8th step modes.
Q2: Is the A3955 available in surface-mount and through-hole packages?
Yes. Package options include a 16-lead batwing SOIC and a 16-pin batwing DIP.
Removed.
Q4: What is the maximum allowable motor supply voltage and current?
50 V and 1.5 A.
Q5: Can the A3955 drive a stepper motor?
Two A3955s, when used in a dual full-bridge configuration, can drive a stepper motor.
Q6: What protection features come with the A3955?
- Thermal shutdown (TSD)
- Crossover current protection
- Under-voltage lockout (UVLO)
- Internal transient-supression diodes
Q7: Do I need any external components?
Yes. The following components are required:
- RS - the external sense resistor. This should be non-inductive.
- RT - the external resistive component needed to set the off time for the PWM current regulator.
- CT - the external active component needed to set the off time for the PWM current regulator. CT also sets the blanking time.
- Decoupling capacitor - logic supply. A 0.01 µF ceramic capacitor is recommended.
- Decoupling capacitor - load supply. A 47 µF electrolytic capacitor is recommended.
Q8: Are there layout concerns that I should be aware of?
Yes. Power ground for the sense resistor, RS, should be connected as close to the device as possible. Also, RS should be non-inductive, and the circuit board ground run should be as large as physically possible. For further layout consideration, please refer to application note 29501.5A "Improving Batwing Power Dissipation."
Q9: Is this a constant-current or constant-voltage controlled device?
Constant-current. Motor winding current is controlled by internal fixed off-time, PWM current-control circuitry.
Q10: How can I increase the current in the winding and not exceed the power rating of the package?
Use external Schottky diodes in parallel with the internal diodes. Heat sinks are also a possibility. However, Schottky diodes are typically the preferred solution.
Q11: Has a technical paper been written for the A3955?
Yes. STP97.5.
Q12: In a dual full-bridge configuration, can one resistor/divider be used to generate both reference voltages and another resistor/divider be used to generate the PFD voltages?
One divider can be used to generate the VREF signal. These pins can be tied together since the internal DAC takes the external signal and processes it. One divider can also be used to provide both PFD inputs, provided that the user does not change modes, i.e. fast, slow, or mixed. To dynamically change the PFD input, the user will have to provide external signals.