LD1117STR

Product Overview

The STMicroelectronics LD1117STR is a series of low-dropout (LDO) linear voltage regulators designed to provide a fixed output voltage with high accuracy, low noise, and low dropout voltage. It is tailored for applications that require stable and efficient voltage regulation with minimal external components. The LD1117STR series offers a combination of excellent line and load regulation, making it suitable for powering analog and digital circuits, microcontrollers, sensors, and other sensitive components in various consumer, industrial, and automotive electronic systems.

Key Features

* Fixed output voltage versions available: 1.8 V, 2.5 V, 3.3 V, and 5 V
* Low dropout voltage typically around 1.2 V at full load (800 mA)
* Output current capability up to 800 mA continuous
* Internal current limit and thermal overload protection
* Reverse-battery protection
* Low quiescent current for efficient operation
* Output voltage accuracy within ±1%
* Fast transient response to load changes
* Internal short-circuit current limiting
* Wide input voltage range up to 15 V (depending on output voltage)
* Output voltage tolerance suitable for powering modern digital circuits
* Stable operation with low ESR ceramic or tantalum capacitors on output
* Available in TO-220 and DPAK packages for efficient thermal dissipation

Electrical Specifications

* Input Voltage Range:

* Maximum: 15 V
* Minimum: Typically 1.1 V above output voltage to maintain regulation
* Output Voltage Options:

* Fixed versions: 1.8 V, 2.5 V, 3.3 V, 5.0 V (depending on specific model)
* Output Current: Up to 800 mA continuous
* Dropout Voltage: Typically 1.2 V at 800 mA load current
* Line Regulation: 0.2 % (typical)
* Load Regulation: 0.3 % (typical)
* Output Voltage Accuracy: ±1% at 25°C
* Quiescent Current: Approximately 5 mA at no load
* Temperature Range: -40 °C to +125 °C operating junction temperature
* Thermal Shutdown Threshold: Approximately 150 °C
* Package Types:

* TO-220 (LD1117STR)
* DPAK (surface mount variant)

Protection Features

The LD1117STR incorporates several internal protection mechanisms designed to safeguard the device and the powered system under abnormal conditions:

* Thermal Shutdown: The regulator shuts down if the junction temperature exceeds approximately 150 °C, preventing damage from overheating. It resumes normal operation once temperature drops.
* Current Limiting: An internal current limit protects the regulator against short circuits or excessive load conditions.
* Reverse Polarity Protection: Protects the device from damage if the input voltage is connected in reverse.
* Safe Operating Area (SOA): Designed to maintain stable operation over a wide range of input voltages, output currents, and thermal conditions.

Thermal Performance and Package

The LD1117STR’s thermal design supports high power dissipation with proper heat sinking or PCB thermal management:

* Thermal Resistance Junction-to-Ambient (RθJA): Approximately 50 °C/W (varies with package and heatsink)
* Thermal Resistance Junction-to-Case (RθJC): Approximately 3 to 5 °C/W
* TO-220 package facilitates easy mounting on heatsinks for enhanced thermal dissipation.
* DPAK package allows for compact surface mount designs but requires adequate PCB copper area for heat sinking.

Applications

* Power supply for microcontrollers, DSPs, and microprocessors
* Post-regulation after switching power supplies for noise-sensitive circuits
* Embedded systems requiring stable low-voltage rails
* Consumer electronics such as set-top boxes, audio devices, and portable instruments
* Industrial control and automation equipment
* Automotive electronic modules with voltage regulation needs
* Sensors and instrumentation circuits requiring clean power rails

Typical Application Circuit

The typical application requires a minimum input capacitor (e.g., 10 µF tantalum or ceramic) to stabilize the input voltage and an output capacitor (minimum 10 µF ceramic or tantalum) for output stability and transient response. The dropout voltage and load current determine the minimum input voltage required for regulation.

Conclusion

The STMicroelectronics LD1117STR series provides a reliable, accurate, and efficient solution for fixed voltage linear regulation in a wide range of applications. Its robust internal protection features, low dropout voltage, and fast transient response make it ideal for powering sensitive electronic circuits where low noise and stable voltage are critical. Available in through-hole and surface-mount packages, it offers flexibility in design and is well-suited for both industrial and consumer electronic products.