STMicroelectronics LD1117S12CTR

Overview

LD1117S12CTR from STMicroelectronics is a fixed-output 1.2 V low-dropout linear voltage regulator in SOT-223 package, delivering up to 800 mA output current with 1.0 V typical dropout at 100 mA, ±1 % output voltage tolerance at 25 °C, and 75 dB supply voltage rejection at 120 Hz - used for post-regulation of 3.3 V or 5 V rails in embedded microcontroller power supplies.

For engineers reviewing the LD1117S12CTR datasheet, LD1117S12CTR pinout, LD1117S12CTR application, or LD1117S12CTR equivalent, key selection criteria include dropout voltage under load, thermal resistance (R_thJA = 110 °C/W), minimum load requirement (2–5 mA), stability with 10 µF ceramic output capacitor, and compatibility with standard SOT-223 PCB footprints.

Technical Context

The LD1117S12CTR employs an NPN pass transistor architecture, enabling high efficiency by routing quiescent current primarily into the load rather than ground - unlike PNP-based regulators. Its internal bandgap reference and error amplifier maintain regulation across input voltages from 2.4 V to 15 V (with ≥1.4 V headroom).

Thermal protection and current limiting are implemented on-die, with junction temperature operating range of −40 °C to +125 °C (C-grade). The device achieves tight initial accuracy via laser trimming and supports stable operation with only a 10 µF output capacitor, eliminating need for ESR-tuned tantalum or electrolytic types.

Key Specifications

Pinout & Package

SOT-223 package (4-pin, single-gauge leadframe) with exposed thermal pad connected internally to V_OUT; pin 1 = IN, pin 2 = GND, pin 3 = OUT, pin 4 = TAB/V_OUT.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TLV70012DCKR and MCP1700T-1202E/TT, LD1117S12CTR provides superior thermal robustness (integrated shutdown), higher output current headroom, and tighter initial accuracy - making it preferred for industrial and medical designs requiring long-term reliability and load flexibility.

Availability

LD1117S12CTR is available at Aetrix Electronics and suitable for industrial automation controllers, medical diagnostic peripherals, and automotive body electronics requiring stable component supply with guaranteed long-term availability and RoHS-compliant packaging.

Supply support for LD1117S12CTR 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 sensor solutions for industrial, automotive, and consumer markets.

The LD1117 series belongs to ST's high-reliability linear regulator product line, engineered specifically for cost-sensitive yet thermally demanding applications where simplicity, robustness, and wide input voltage range are critical.

FAQ

What is the minimum input voltage required for stable 1.2 V output at 800 mA?

The LD1117S12CTR requires a minimum input-to-output differential voltage of 1.10 V at 800 mA (per Table 3, "Vd Dropout voltage" row). Therefore, minimum input voltage is 1.2 V + 1.10 V = 2.3 V. However, ST specifies absolute minimum VIN as 2.4 V in practice to ensure margin across temperature and process variation.

Can LD1117S12CTR operate without an output capacitor?

No. The LD1117S12CTR requires a minimum 10 µF ceramic output capacitor for stability, as confirmed in Section 4 ("Schematic application") and Table 3 notes. Omitting it causes oscillation and unregulated output due to phase margin loss in the internal control loop.

Is the SOT-223 thermal pad electrically isolated?

No. Per Figure 2 and datasheet note "The TAB is connected to the VOUT", the SOT-223 thermal pad (Pin 4) is internally bonded to the output terminal. It must be routed to the same net as V_OUT and soldered to a dedicated copper pour - not to ground or any other potential.

Does LD1117S12CTR support reverse-voltage protection?

No. The LD1117S12CTR lacks built-in reverse-voltage protection. If input polarity may be reversed, an external series Schottky diode (e.g., 1N5819) must be added between VIN and the regulator input pin to prevent catastrophic failure.