A4950
Full-bridge motor driver with PWM current control for brushed DC motors up to 40V and 3.5A.
Product Overview
Description
The A4950 is a full-bridge DC motor driver designed to drive brushed DC motors in automotive and industrial applications. The device features internal PWM current control that regulates motor current without microcontroller intervention, simplifying system design.
The integrated charge pump eliminates the need for external capacitors while providing sufficient gate drive voltage for low RDS(on) operation. The A4950 can drive motors with supply voltages up to 40V and continuous currents up to 3.5A, with peak currents up to 5A.
Comprehensive protection features include overcurrent protection, thermal shutdown, undervoltage lockout, and cross-conduction prevention. The device includes diagnostic outputs that indicate fault conditions to the system controller.
Product Series
A
Primary Application
Automotive HVAC actuators
Key Features
- Internal PWM current control
- Integrated charge pump
- Low RDS(on) for efficient operation
- Simple logic-level control inputs
- Current sense output for monitoring
- Comprehensive fault protection
- Diagnostic fault output
- AEC-Q100 automotive qualified
Specifications
| Motor Type | Brushed DC |
|---|---|
| Supply Voltage | 8V to 40V |
| Output Current | 3.5A continuous, 5A peak |
| RDS(on) | 350mΩ total (high+low side) |
| PWM Frequency | Up to 50kHz |
| Current Control | Internal PWM regulation |
| Protection | OCP, OTP, UVLO, cross-conduction |
| Package | SOIC-8, QFN-16 |
| Temperature Range | -40°C to +125°C |
Applications
Automotive HVAC actuators
Automotive and EV electronics
Mirror adjustment motors
Motor drive and control systems
Seat adjustment systems
Electronic system design
Window lift motors
Motor drive and control systems
Industrial valve control
Industrial automation and control
Pump and fan drives
Motor drive and control systems
FAE Expert Insights
"The A4950 is my go-to solution for automotive DC motor control. The internal PWM current control is a standout feature - it automatically regulates motor current without requiring the microcontroller to generate PWM signals. This simplifies software development and reduces EMI by using the driver's internal oscillator. The integrated charge pump is another plus, eliminating external capacitors and reducing BOM cost. I've used this part in mirror adjustment, HVAC flap control, and seat adjustment applications with excellent reliability. The diagnostic output is valuable for automotive systems - it can detect open-load, short-circuit, and overtemperature conditions. Key design tips: Use the current sense resistor to set the current limit based on motor specifications; ensure adequate PCB copper area for thermal management; the device can get warm at 3.5A continuous operation. The AEC-Q100 qualification is essential for automotive applications. Overall, a reliable and easy-to-use DC motor driver."
Internal PWM current control simplifies design; integrated charge pump reduces BOM; diagnostic output for fault detection
— Mark Thompson, BeiLuo
Frequently Asked Questions
How does the internal PWM current control work?
The A4950's internal PWM current control automatically regulates motor current: Current sensing - internal sense resistor monitors motor current; Comparator - compares sensed current to reference; PWM generation - internal oscillator generates PWM when current exceeds limit; H-bridge control - PWM modulates bridge to maintain average current. Operation: When current < limit: both low-side switches on, current increases; When current > limit: switches alternate, current decreases; Average current maintained at programmed level. Benefits: No microcontroller PWM required; fixed frequency reduces EMI; automatic current regulation; protects motor from overcurrent. Configuration: Set current limit via sense resistor; PWM frequency fixed at ~25kHz (inaudible); Current ripple typically 10-20% of limit. The internal control loop operates independently, freeing the microcontroller for other tasks.
Internal PWM eliminates MCU PWM generation; fixed 25kHz frequency; automatic current regulation.
What is the diagnostic output used for?
The A4950 diagnostic output (DIAG) provides fault indication: Fault types detected - Overcurrent (short circuit); Overtemperature (thermal shutdown); Undervoltage (UVLO active); Open load (no motor connected). Output behavior: Normal operation: DIAG pin high (pulled up); Fault condition: DIAG pin low (pulled down); Multiple faults: Pin stays low until all faults cleared. Connection options: Connect to microcontroller GPIO with pull-up; Or connect to LED with current limit resistor; Or use for system shutdown circuit. Software implementation: Poll DIAG pin periodically; Or configure as interrupt for immediate response; Read pin state to detect faults; Take appropriate action (stop motor, log fault, etc.). The diagnostic feature is essential for automotive applications requiring fault detection and reporting.
DIAG pin goes low during faults; connect to MCU or LED; essential for automotive fault detection.
How do I set the current limit for my motor?
Setting the A4950 current limit: Formula - I_limit = V_ref / (8 × R_sense); Where V_ref is internal 1V reference, R_sense is external sense resistor. Calculation example: For 2A current limit: R_sense = 1V / (8 × 2A) = 0.0625Ω = 62.5mΩ; Use standard 62mΩ resistor. For 3A current limit: R_sense = 1V / (8 × 3A) = 0.0417Ω = 41.7mΩ; Use standard 43mΩ or 39mΩ resistor. Resistor selection: Use low-inductance resistors (metal film or chip resistors); Power rating: P = I² × R (e.g., 3A × 3A × 0.043Ω = 0.39W, use 1W resistor); Tolerance: 1% or better for accurate current limit. Verification: Measure voltage across sense resistor at max current; Should be V = I × R_sense; Adjust resistor if needed. Always set current limit 20-30% above motor rated current for margin.
Use I_limit = V_ref / (8 × R_sense); set 20-30% above motor rating; use 1% tolerance resistors.
What thermal management is required for A4950?
A4950 thermal management guidelines: Power dissipation calculation - P = I² × Rds(on) for conduction losses; Rds(on) = 350mΩ total (high+low side); At 3A: P = 9 × 0.35 = 3.15W; At 2A: P = 4 × 0.35 = 1.4W. Temperature rise: T_rise = P × θja; θja depends on PCB design (typically 40-60°C/W for SOIC-8); At 3A with 50°C/W: T_rise = 3.15 × 50 = 157°C (exceeds limit). Thermal design: Use large copper area (≥ 1 oz) for heat spreading; Add thermal vias under package to inner layers; Consider exposed pad package for better thermal performance; Add heatsink for continuous high-current operation. Operating limits: Maximum junction temperature: 150°C; Recommended maximum: 125°C for reliability; Thermal shutdown activates at 165°C. For continuous 3A operation, forced air cooling or heatsink may be required.
Calculate P = I² × Rds(on); use copper area and vias; consider heatsink for > 2.5A continuous.
Can A4950 drive motors in both directions?
Yes, the A4950 full-bridge configuration supports bidirectional motor control: Forward direction - IN1 high, IN2 low: current flows from OUT1 to OUT2; motor rotates clockwise; Reverse direction - IN1 low, IN2 high: current flows from OUT2 to OUT1; motor rotates counter-clockwise; Brake/coast - both inputs high or both low: motor braking or coasting. Control logic: IN1 | IN2 | Function; 0 | 0 | Coast (both outputs high-impedance); 1 | 0 | Forward (current OUT1→OUT2); 0 | 1 | Reverse (current OUT2→OUT1); 1 | 1 | Brake (both outputs low). PWM speed control: Apply PWM to enable pin for speed control; Or alternate between forward and coast for PWM control; Current regulation active in all modes. The full-bridge topology provides complete motor control with direction, speed, and braking capability using just two logic inputs.
Full-bridge supports forward, reverse, brake, coast; use IN1/IN2 inputs for direction control.