The STMicroelectronics L4940V5 is a low-dropout (LDO) linear voltage regulator designed to provide a fixed 5 V output from a higher input voltage while delivering high output current with low quiescent current. Part of ST’s L4940 series, it combines excellent line and load regulation, thermal protection, and short-circuit protection in a compact package, making it suitable for a wide range of industrial, consumer, and automotive applications. The L4940V5 is particularly optimized for powering digital circuits, microcontrollers, sensors, and peripheral devices that require stable 5 V operation even under varying input and load conditions.

## Electrical Specifications

The L4940V5 is designed to operate with a maximum output current of 1 A and provides a nominal 5 V output with high accuracy. Its electrical characteristics include:

* Input voltage range (V_IN): 6 V to 20 V, allowing operation from standard 12 V or 24 V power rails.
* Output voltage (V_OUT): 5 V nominal, with a typical tolerance of ±2% under full load.
* Maximum output current: 1 A continuous.
* Dropout voltage (V_DO): typically 0.5 V at full load (1 A), ensuring regulated output even when input voltage is close to the output.
* Line regulation: typically 0.2% over the full input range.
* Load regulation: typically 0.3% for load changes from 10 mA to 1 A.
* Quiescent current (I_Q): approximately 6 mA under no-load conditions, minimizing power loss.
* Output noise: typically 40 μV RMS in the 10 Hz–100 kHz bandwidth.

The device includes thermal shutdown with hysteresis, ensuring safe operation in case of overtemperature conditions. It also incorporates short-circuit protection with constant current limiting to protect both the regulator and downstream circuits.

## Thermal and Mechanical Characteristics

The L4940V5 is packaged in a TO-220 or TO-220F plastic package with three leads, allowing straightforward mounting on PCBs with or without heatsinks. Its junction temperature range is specified from −40°C to +150°C, and the device operates reliably under extended thermal conditions typical of automotive and industrial environments.

The regulator features low thermal resistance (R_θJA and R_θJC) allowing efficient heat dissipation when paired with appropriate copper planes on the PCB or an external heatsink. Maximum power dissipation is a function of the voltage drop between input and output multiplied by the output current; careful thermal design is required to ensure the junction temperature does not exceed the maximum rating during high-current or high-dropout operation.

## Protection Features

The L4940V5 integrates multiple protection mechanisms:

* Thermal shutdown: disables output when junction temperature exceeds 150°C, automatically restoring operation once temperature falls below the threshold.
* Short-circuit protection: limits output current to a safe value to prevent damage during accidental shorts or load faults.
* Safe area protection: prevents the internal pass transistor from exceeding safe power dissipation under high input voltage and full-load conditions.

These protections enhance reliability and system safety in applications prone to transients, overloads, or thermal stress.

## Performance Characteristics

The L4940V5 maintains excellent transient response with minimal output voltage deviation for fast load changes, making it suitable for digital circuits requiring stable supply during sudden current spikes. The device achieves low output noise and high ripple rejection (typically 60 dB at 120 Hz), ensuring clean 5 V power for sensitive analog and digital devices.

The dropout voltage is characterized under various load currents, remaining below 0.7 V for currents up to 1 A. Line and load regulation ensure minimal voltage variation over wide input voltage swings and load changes, keeping output voltage within tight limits.

## Applications

The L4940V5 is widely used in applications where regulated 5 V power is required with high reliability and compact design:

* Industrial control systems and automation electronics
* Microcontroller and FPGA power supply rails
* Automotive electronics including sensors, actuators, and infotainment modules
* Consumer electronics such as set-top boxes, home appliances, and networking equipment
* Point-of-load regulation for distributed power architectures
* Instrumentation and measurement systems requiring low-noise 5 V supply

Its low dropout, protection features, and thermal robustness make it suitable for both board-mounted and embedded power solutions.

## Performance Parameters Summary

* Input voltage range: 6–20 V
* Output voltage: 5 V ±2%
* Maximum output current: 1 A
* Dropout voltage: 0.5 V typical at 1 A
* Line regulation: 0.2% typical
* Load regulation: 0.3% typical
* Quiescent current: 6 mA typical
* Output noise: 40 μV RMS typical
* Thermal shutdown: Yes, with hysteresis
* Short-circuit protection: Yes, constant current limiting
* Junction temperature range: −40°C to +150°C
* Package: TO-220 or TO-220F plastic, 3-pin, with heatsink compatibility
* Ripple rejection: 60 dB typical at 120 Hz
* Environmental compliance: RoHS

## Design Considerations

Designers must ensure proper heat dissipation when operating near maximum current and input voltage to prevent thermal shutdown. Adequate copper area on the PCB or the use of external heatsinks reduces junction temperature rise. Input and output capacitors are recommended for stability and transient suppression, typically a 0.33 μF ceramic input capacitor and a 22 μF electrolytic or tantalum output capacitor. The choice of capacitor ESR affects loop stability and transient performance.

For automotive applications, careful consideration of load dumps, input surges, and transients is necessary, and protective components such as TVS diodes can be included. Layout should minimize inductive loops and place bypass capacitors close to the regulator pins to ensure low-noise operation.

## Summary

The STMicroelectronics L4940V5 is a robust, low-dropout linear regulator delivering 5 V at up to 1 A with low quiescent current, excellent line and load regulation, and integrated thermal and short-circuit protections. Its compact TO-220 package, low noise, and high reliability make it suitable for industrial, automotive, and consumer applications requiring stable 5 V power under variable input and load conditions. The device’s combination of performance, protection, and thermal efficiency provides designers with a versatile solution for regulated 5 V power in a wide range of systems.