LD1117S50CTR

The STMicroelectronics LD1117S50CTR is a low-drop positive voltage regulator capable of providing up to 800mA of output current at a fixed 5.0V. The NPN pass transistor ensures high efficiency since the quiescent current flows mostly into the load, unlike PNP-based LDOs. The on-chip trimming allows the regulator to achieve very tight output voltage tolerance of +-1% at 25C. With a typical dropout voltage of only 1V at 800mA, the LD1117 is suitable for applications where the input-to-output voltage differential is limited. A minimum 10uF output capacitor is required for stability. The device includes internal current limiting and thermal shutdown protection for reliable operation.

The LD1117S50CTR operates as a series-pass linear regulator using an NPN pass transistor topology: 1) Reference and Error Amplifier: A bandgap voltage reference generates a stable internal reference voltage. The error amplifier continuously compares the output feedback with this reference and drives the NPN pass transistor to maintain the output at 5.0V. 2) NPN Pass Element: Unlike PNP-based LDOs, the NPN pass transistor draws its base current from the input supply, and the quiescent current flows into the load rather than to ground. This results in higher efficiency, especially at lighter loads. The dropout voltage is determined by the VCE(sat) of the NPN transistor, typically 1V at 800mA. 3) Protection: Internal current limiting prevents excessive output current, and thermal shutdown protects the device from overheating during fault conditions.

• 5V power regulation from 6.5V-15V sources in embedded systems
• Post-regulation after switching converters for low-noise 5V rails
• Battery-powered equipment requiring efficient 5V regulation
• Consumer electronics and computer peripheral power supplies
• Industrial control systems with 9V or 12V input sources