LDL1117S25R

The STMicroelectronics LDL1117S25R is a 1.2A high-PSRR low-dropout linear voltage regulator providing a fixed 2.5V output from an input voltage range of 2.6V to 18V. With a typical dropout voltage of only 350mV at 1.2A, it is suitable for applications where the input-to-output differential is small. The high power supply rejection ratio of 87dB at 120Hz, rolling down to more than 40dB at 100kHz, makes the LDL1117 particularly suitable for direct regulation in switch-mode power supplies and secondary linear regulation in DC-DC converters. The device includes comprehensive protection with current limit, safe operating area (SOA), and thermal shutdown. Stable operation is achieved with ceramic output capacitors as small as 1uF.

The LDL1117S25R operates as a series-pass linear regulator with four key functional blocks: 1) Bandgap Reference: A precision bandgap voltage reference generates the internal reference voltage. The 2.5V output is derived from this reference through laser-trimmed resistive dividers, ensuring +-2% initial accuracy. 2) Error Amplifier: The error amplifier compares a fraction of the output voltage with the bandgap reference and drives the pass transistor to maintain regulation. The compensation is designed for stability with ceramic capacitors from 1uF to 100uF. 3) Pass Element: The NPN pass transistor provides the current path from input to output with low dropout voltage of 350mV at 1.2A. 4) Protection Circuits: Current limiting, SOA protection, and thermal shutdown (junction temperature limit) safeguard the device against overload, excessive power dissipation, and thermal stress conditions.

• SMPS secondary-side post-regulation for noise-sensitive circuits
• Point-of-load 2.5V regulation on industrial and consumer motherboards
• DC-DC converter output cleanup with high PSRR
• Battery-powered devices requiring stable 2.5V rail
• Low-voltage FPGA and CPLD core power supply