A4950ELJTR-T

The A4950ELJTR-T is a fully integrated DMOS full-bridge motor driver IC from Allegro MicroSystems. It provides a complete single-chip solution for driving DC brushed motors with pulse-width modulation (PWM) control, featuring integrated power MOSFETs, current sensing, and comprehensive fault protection.

Capable of sourcing and sinking up to 3.5A peak output current and operating from supply voltages between 8V and 40V, the A4950 is well-suited for a wide range of motor applications including office automation, industrial equipment, consumer products, and automotive subsystems. The full-bridge topology supports both forward and reverse motor operation as well as coast and brake modes, all controlled via the two logic input pins (IN1 and IN2).

A key feature of the A4950 is its integrated current regulation system. The VREF pin sets the current limit threshold, and an internal current sense amplifier with a typical gain of 10V/V provides proportional current sensing through the LSS (low-side sense) pin. This allows the system designer to implement accurate current limiting for motor torque control or stall detection without external current sense amplifiers.

Synchronous rectification is automatically activated during PWM operation, significantly reducing power dissipation by conducting current through the low-resistance MOSFET channel instead of the body diode. This improves efficiency and reduces thermal buildup, especially at higher current levels.

The device incorporates a comprehensive set of protection features including overcurrent protection, motor short-to-ground and short-to-supply detection, thermal shutdown with hysteresis, undervoltage lockout, and crossover-current (shoot-through) protection. The A4950ELJTR-T is supplied in an 8-pin SOICN package with an exposed thermal pad for optimal thermal performance, with 3000 pieces per 13-inch reel.

The A4950 full-bridge motor driver operates by controlling four DMOS power transistors arranged in an H-bridge configuration to drive a DC motor. Here’s a breakdown of its operation:

1. Full-Bridge Power Stage: Four N-channel DMOS transistors are arranged in an H-bridge (full-bridge) topology. Two high-side MOSFETs connect the motor terminals to VBB, while two low-side MOSFETs connect them to ground (LSS). By selectively turning on different pairs of MOSFETs, current can be directed through the motor in either direction (forward/reverse), or the motor can be shorted (brake) or disconnected (coast).

2. Input Logic and Decoding: The IN1 and IN2 logic inputs control the bridge configuration. A truth table determines the output state: IN1=H/IN2=L = forward (OUT1=VBB, OUT2=GND); IN1=L/IN2=H = reverse (OUT1=GND, OUT2=VBB); IN1=L/IN2=L = coast (both high-side off); IN1=H/IN2=H = brake/slow decay (both low-side on). Inputs are 3.3V/5V compatible with hysteresis for noise immunity.

3. Charge Pump: Since all four MOSFETs are N-channel, an internal charge pump generates a voltage above VBB to properly drive the gates of the high-side MOSFETs. The charge pump operates at high frequency and requires no external components.

4. Current Sensing and Regulation: The low-side MOSFETs have integrated current sensing that produces a proportional current at the LSS pin. An internal sense amplifier with a gain of approximately 10V/V compares the sensed current with the VREF reference voltage. When the load current reaches the threshold set by VREF, the current limit circuit activates, cycling the output to maintain constant current.

5. Synchronous Rectification: During PWM operation (when the current is recirculating), the A4950 automatically turns on the appropriate MOSFETs to conduct the recirculation current through the low RDS(on) channel rather than through the body diode. This reduces power dissipation and improves efficiency significantly compared to diode-based freewheeling.

6. Overcurrent Protection (OCP): If the output current exceeds the OCP threshold (significantly above the normal operating range), the device immediately limits the current to protect the power MOSFETs and the load. This protects against short-circuit conditions at the motor terminals.

7. Thermal Shutdown: An on-chip temperature sensor monitors the junction temperature. If TJ exceeds approximately 165°C, the device enters thermal shutdown, disabling all outputs. Hysteresis of approximately 25°C ensures the device restarts only after sufficient cooling.

8. Undervoltage Lockout (UVLO): If the supply voltage VBB drops below the UVLO threshold, all outputs are disabled to prevent undefined operation. The device automatically restarts when VBB returns above the threshold with hysteresis to prevent chattering.

Package: SOICN-8 (8-lead small outline package with exposed thermal pad). Body dimensions: approximately 4.9mm × 3.9mm, 1.27mm lead pitch. Exposed pad on bottom for enhanced thermal dissipation.

• Office Automation Equipment: Paper feed motors, carriage drives, and stepper motor replacements in printers, scanners, multifunction devices, and copiers, where the A4950 provides efficient PWM speed control with built-in current limiting and protection.
• Robotics and Actuators: DC motor drive for small robotic platforms, robotic arms, grippers, and linear actuators in industrial automation, educational robots, and hobbyist robotics projects requiring bidirectional speed control.
• Home Appliances: Motor control in white goods such as washing machines, dishwashers, refrigerators, and small kitchen appliances, driving pumps, valves, fans, and actuator motors with reliable overcurrent and thermal protection.
• Consumer Electronics: Camera lens autofocus and zoom motors, projector lens controls, DVD/Blu-ray drive motors, and other consumer devices requiring compact, efficient, low-voltage DC motor control with minimal external components.
• Industrial Valves and Solenoids: Driving solenoid valves and proportional solenoids in industrial process control, pneumatic systems, and hydraulic control systems, where the current regulation feature enables precise force or position control.
• Automotive Subsystems: Non-safety automotive applications such as seat adjustment motors, mirror positioning, HVAC blower motors, and small actuators (note: A4950K automotive grade version available for AEC-Q100 requirements).
• Battery-Powered Motor Control: Portable and battery-operated motor drives in power tools, garden equipment, and handheld devices, where the low standby current (10µA) helps preserve battery life during idle periods.
• Medical and Healthcare Devices: Small motor and pump control in medical infusion pumps, diagnostic equipment, dental tools, and lab automation devices requiring reliable, compact motor drive with overcurrent protection for safety.

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