STMicroelectronics LDL1117S18R

Overview

LDL1117S18R from STMicroelectronics is a fixed 1.8 V, 1.2 A low-dropout linear voltage regulator in SOT223 package, featuring 350 mV typical dropout at full load, 87 dB PSRR at 120 Hz, and operation from 2.5 V to 18 V input. It delivers stable local regulation for FPGA core supplies, microcontroller I/O rails, and industrial sensor interfaces requiring tight output accuracy (±2% at 25°C) and thermal robustness (−40°C to 125°C).

For engineers reviewing the LDL1117S18R datasheet, LDL1117S18R pinout, LDL1117S18R application, or LDL1117S18R equivalent, this page provides verified technical context, validated pin functions, confirmed thermal protection behavior, and real-world use cases in DC-DC post-regulation and motherboard point-of-load systems.

Technical Context

The LDL1117S18R employs a PNP pass transistor architecture enabling low dropout and high PSRR across low-to-mid frequencies. Its internal current limiting (typ. 2 A), SOA-based power foldback, and thermal shutdown (175°C trip, 150°C recovery) operate without external components.

Stability is guaranteed with ≥1 μF input and ≥4.7 μF ceramic output capacitance (X5R/X7R recommended); ESR requirements are relaxed due to internal compensation. The device supports fast transient response in SMPS secondary regulation thanks to its 60 µV_RMS output noise (10 Hz–100 kHz) and 80 dB PSRR at 1 kHz.

Key Specifications

Pinout & Package

LDL1117S18R uses the SOT223 package with exposed thermal tab connected internally to VOUT, enabling direct PCB copper pour for enhanced thermal dissipation (θ_J-C = 15°C/W). Mounting requires soldering the tab to a large copper area for optimal junction temperature control.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar LDO regulator applications.

Compared with TLV1117-18CDCYR and MCP1703T-1802E/MB, the LDL1117S18R uniquely combines 1.2 A capability, 350 mV dropout, and SOA-based current limiting - making it the only option among the three qualified for sustained 1.2 A loads in thermally constrained industrial enclosures.

Availability

LDL1117S18R is available at Aetrix Electronics and suitable for FPGA core supply, industrial sensor node, and SMPS post-regulation applications requiring stable component supply, long-term lifecycle assurance, and traceable sourcing.

Supply support for LDL1117S18R includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing analog, MCU, power, and sensing solutions for industrial, automotive, and consumer markets.

The LDL1117 series belongs to ST's high-PSRR, high-current LDO portfolio, engineered specifically for demanding DC-DC post-regulation and motherboard point-of-load applications where noise immunity and thermal resilience are critical.

FAQ

What is the minimum input voltage required for stable 1.8 V output at 1.2 A?

The LDL1117S18R requires VIN ≥ VOUT + VDROP = 1.8 V + 0.6 V = 2.4 V (max dropout) to maintain regulation at full load. With typical dropout of 350 mV, 2.15 V input suffices under nominal conditions. Absolute minimum VIN per datasheet is 2.5 V for guaranteed operation across temperature and process variation.

Can the SOT223 thermal tab be left floating during PCB layout?

No - the tab is internally connected to VOUT per datasheet Table 1 and Figure 2. Leaving it unconnected creates a parasitic thermal bottleneck and risks exceeding θ_J-A = 120°C/W, leading to premature thermal shutdown. It must be soldered to a dedicated VOUT copper pour with ≥4 thermal vias to inner ground planes.

Does the LDL1117S18R require an external shutdown pin for power sequencing?

No - the device has no enable/shutdown pin. It turns on automatically when VIN exceeds the 2.4 V turn-on threshold with 200 mV hysteresis. For controlled sequencing, an external MOSFET switch on VIN or a discrete supervisor IC is required to gate input power.

How does the SOA protection differ from standard current limiting?

Standard current limiting clamps output at ~2 A regardless of VIN–VOUT. SOA protection reduces that limit proportionally as (VIN–VOUT) increases - e.g., at 5 V dropout, peak current drops to ~1.5 A - preventing simultaneous high voltage and high current that would exceed safe operating area and cause junction overheating.