STMicroelectronics LD1117ASTR

Overview

LD1117ASTR from STMicroelectronics is an adjustable low-dropout linear voltage regulator delivering up to 1 A output current with a 1.25 V internal reference voltage, 1.15 V typical dropout at 1 A, ±2% output voltage tolerance at 25 °C, and high 80 dB supply voltage rejection - used in post-regulation stages of power supplies for microcontrollers and analog sensors.

For engineers reviewing the LD1117ASTR datasheet, LD1117ASTR pinout, LD1117ASTR application, or LD1117ASTR equivalent, key selection criteria include dropout voltage at full load, thermal resistance in SOT-223 package, minimum 10 µF output capacitance requirement, and adjustment pin current (60–120 µA) for precision external resistor networks.

Technical Context

The LD1117ASTR uses an NPN pass transistor architecture enabling low dropout while maintaining stability with only 10 µF ceramic or electrolytic output capacitance. Its internal 1.25 V bandgap reference is thermally stabilized and trimmed to ±2% accuracy at 25 °C, supporting precise external voltage setting via two-resistor feedback.

Thermal regulation is managed by integrated current and thermal limiting circuits, with junction-to-ambient thermal resistance of 110 °C/W in SOT-223. The ADJ pin draws only 60 µA typ., minimizing error contribution from resistor divider current mismatch across temperature and load conditions.

Key Specifications

Pinout & Package

LD1117ASTR is supplied in SOT-223 package with exposed thermal pad connected internally to VOUT. This configuration provides 110 °C/W junction-to-ambient thermal resistance and requires PCB copper pour under the tab for effective heat dissipation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TLV1117-ADJ and MCP1703T-ADJ, the LD1117ASTR balances moderate dropout (1.15 V), industry-standard 5 mA IQ, and full adjustability - making it optimal for industrial and embedded designs requiring both precision and thermal robustness without sacrificing layout simplicity.

Availability

LD1117ASTR is available at Aetrix Electronics and suitable for industrial PLC I/O modules, medical sensor front-ends, and IoT edge node power management requiring stable component supply across multi-year production cycles.

Supply support for LD1117ASTR 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 silicon solutions for automotive, industrial, and consumer markets since 1987.

The LD1117A series belongs to ST's legacy linear regulator product line, engineered specifically for cost-sensitive, thermally demanding applications where reliability, wide input range, and compatibility with standard passive components are prioritized over ultra-low IQ or digital control.

FAQ

What is the minimum output capacitance required for LD1117ASTR stability?

The LD1117ASTR requires a minimum 10 µF output capacitor with ≤1 Ω ESR for guaranteed stability across all loads and temperatures. Aluminum electrolytic, tantalum, or polymer capacitors meeting this specification are acceptable; ceramic capacitors may require series resistance to meet ESR requirements.

Can LD1117ASTR be used in parallel to increase output current?

No - LD1117ASTR is not designed for parallel operation. Its output voltage tolerance (±2%) and thermal drift characteristics prevent balanced current sharing. For >1 A applications, select a higher-current regulator or implement active current-sharing circuitry with external op-amps and sense resistors.

What is the maximum allowable input-to-output voltage differential for continuous operation?

The absolute maximum input voltage is 15 V, but continuous operation depends on power dissipation. At 1 A output and 1.15 V dropout, 13.85 V input yields 12.7 W dissipation - exceeding the 12 W absolute maximum rating for SOT-223. Derating is required above ~11 V input at full load to maintain safe junction temperature.

How does the ADJ pin current affect output voltage accuracy in adjustable configurations?

The ADJ pin draws 60–120 µA, flowing through the lower resistor (R1) in the feedback divider. This introduces a systematic offset: VOUT = VREF × (1 + R2/R1) + I_ADJ × R2. For R2 = 2.4 kΩ, this adds up to 0.288 mV error - negligible for most applications but must be compensated in precision metrology designs using low-R2 values or buffered references.