Product Overview

The STMicroelectronics L9651 is a dedicated stepper motor driver IC designed for driving bipolar stepper motors in a cost-effective and compact manner. It integrates a full H-bridge output stage with embedded current regulation, allowing precise control of the motor current and thereby improving motor performance and efficiency. The device supports microstepping, enabling smooth and quiet motor operation, which is especially important in applications requiring high precision and low noise.

The L9651 is optimized for use in applications such as printers, scanners, office automation equipment, robotics, and other embedded systems where efficient and reliable stepper motor control is essential. It features built-in protections including thermal shutdown, undervoltage lockout, and short-circuit protection, ensuring robust operation under adverse conditions.

Housed in a compact PowerSO-20 package, the L9651 simplifies the overall design by reducing the external component count and saving board space, while providing flexible control and adjustable current settings.

Key Features

* Bipolar stepper motor driver with full H-bridge outputs
* Integrated current regulation with adjustable output current up to 1.5 A RMS
* Supports microstepping with up to 1/16 step resolution
* Operating supply voltage (motor voltage) up to 40 V
* Logic supply voltage range: 4.5 V to 5.5 V
* PWM current control with programmable decay modes (fast, slow, mixed)
* Step and direction inputs compatible with TTL/CMOS logic levels
* Built-in protection features: thermal shutdown, undervoltage lockout, short-circuit protection, and overcurrent detection
* Low quiescent current consumption in standby mode
* Fault output indicator to signal driver or motor faults
* Operating temperature range: –40°C to +125°C
* Compact PowerSO-20 package ensuring efficient thermal dissipation and easy mounting
* Minimal external components required for current sensing and filtering

Electrical Specifications

* Motor Supply Voltage (VM): 8 V to 40 V
* Logic Supply Voltage (VDD): 4.5 V to 5.5 V
* Output Current (IO): Up to 1.5 A RMS continuous per phase
* Peak Output Current: Approximately 2.0 A (limited by package thermal dissipation)
* Step Input Frequency: Up to 100 kHz typical
* Output Voltage Drop: 1.3 V typical at 1 A load
* PWM Frequency: Adjustable, typically in the range 20 kHz to 30 kHz
* Thermal Shutdown Threshold: Typically 150°C junction temperature
* Undervoltage Lockout Threshold: Approximately 3.8 V for logic supply
* Input Logic Thresholds: TTL/CMOS compatible (minimum VIH = 2.0 V, maximum VIL = 0.8 V)
* Standby Current: Less than 5 mA typical
* Operating Temperature Range: –40°C to +125°C
* Package: PowerSO-20

Functional Description

The L9651 integrates a dual full-bridge driver capable of independently controlling two phases of a bipolar stepper motor. The motor current is regulated through a closed-loop PWM scheme using an external sense resistor. This current regulation reduces power dissipation and improves motor torque consistency across varying speeds.

The device accepts step and direction signals for motor positioning, simplifying the control interface. The microstepping capability divides each full step into smaller steps, thereby reducing vibration and noise, and enhancing positional accuracy.

Multiple decay modes are supported for current regulation to optimize motor performance under different load and speed conditions. The user can select between fast decay, slow decay, and mixed decay via external pin configurations.

Protection circuits within the L9651 include thermal shutdown to prevent overheating, undervoltage lockout to avoid malfunction under low voltage conditions, and short-circuit detection to protect the device and motor in fault conditions. A fault output pin signals any detected abnormal conditions for system-level fault management.

The device requires only a few external components such as sense resistors, decoupling capacitors, and a bootstrap diode for proper operation, minimizing overall system complexity.

Typical Applications

* Printers and scanners requiring precise stepper motor control
* Office automation equipment such as copiers and fax machines
* Robotics and automated machinery
* Textile and packaging machines with stepper motor drives
* CNC machines and positioning systems
* Consumer electronics with stepper motor actuation
* Medical devices requiring reliable motor positioning

Design Considerations

* Sense Resistor Selection: Choose low-inductance precision resistors with appropriate power rating for current sensing to achieve accurate current regulation.
* Power Supply Decoupling: Use low-ESR ceramic capacitors close to the VM and VDD pins to minimize voltage spikes and improve switching stability.
* Thermal Management: Ensure adequate heat sinking and PCB copper area for thermal dissipation, especially when driving currents near maximum ratings.
* Input Signal Integrity: Provide clean, debounce-free step and direction signals to avoid missteps or erratic motor behavior.
* Bootstrap Circuitry: Proper bootstrap diode and capacitor sizing is required for the high-side MOSFET driver to maintain stable high-side voltage.
* PCB Layout: Minimize parasitic inductance on sense resistor and gate drive traces to enhance performance and reduce EMI.
* Current Limiting and Protection: Design system-level safeguards in conjunction with the internal protection features to ensure safe operation.
* Fault Handling: Monitor fault output pin for timely detection and mitigation of fault conditions.

Summary

The STMicroelectronics L9651 is a highly integrated, robust stepper motor driver IC providing accurate current control, microstepping capability, and extensive protection features in a compact package. Its flexible PWM current regulation and selectable decay modes ensure optimized motor performance across various operating conditions. With minimal external components and a straightforward control interface, the L9651 facilitates the design of efficient, precise, and quiet bipolar stepper motor drive systems suitable for a broad range of industrial and consumer applications.