STMicroelectronics LD1117AS33TR

Overview

LD1117AS33TR from STMicroelectronics is a fixed-output 3.3 V low-dropout linear voltage regulator delivering up to 1 A output current with 1.15 V typical dropout at full load, ±2% output voltage tolerance at 25 °C, and 80 dB supply voltage rejection at 120 Hz - used for post-regulation in microcontroller power rails, USB peripheral supplies, and industrial sensor interfaces.

For engineers reviewing the LD1117AS33TR datasheet, LD1117AS33TR pinout, LD1117AS33TR application, or LD1117AS33TR equivalent, key selection criteria include dropout voltage at 1 A, thermal resistance (R_thJA = 110 °C/W in SOT-223), minimum stability capacitor (10 µF), quiescent current (5 mA typ.), and fixed 3.3 V output accuracy across 0–125 °C.

Technical Context

The LD1117AS33TR employs an NPN pass transistor architecture enabling low dropout while maintaining high PSRR (60–80 dB) and low output noise (100 µV RMS, 10 Hz–10 kHz). Its internal thermal and current limiting protect against fault conditions without external components.

It operates over 4.75–10 V input range with 3.3 V nominal output, supports 0–1 A load current, and achieves ±0.5% temperature stability and 0.3% long-term drift after 1000 hrs at 125 °C junction temperature - confirming suitability for thermally constrained embedded systems.

Key Specifications

Pinout & Package

LD1117AS33TR is supplied in SOT-223 package with exposed thermal pad electrically connected to V_OUT. The package provides R_thJA = 110 °C/W and R_thJC = 15 °C/W, enabling 1 A operation with minimal heatsinking on standard 2-layer PCBs.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TLV1117-33CDCR and MCP1700-3302E/TO, LD1117AS33TR uniquely balances 1 A capability, 125 °C operation, and 80 dB PSRR in SOT-223 - making it optimal for thermally demanding, noise-sensitive industrial and automotive body applications where both current and robustness are non-negotiable.

Availability

LD1117AS33TR is available at Aetrix Electronics and suitable for industrial PLC I/O modules, USB-C peripheral power designs, and wireless sensor nodes requiring stable component supply with guaranteed long-term manufacturability and consistent parametric performance.

Supply support for LD1117AS33TR 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, power, microcontroller, and sensor solutions for industrial, automotive, and consumer markets.

The LD1117A series was developed as a cost-optimized, high-reliability LDO family targeting space-constrained embedded systems requiring precise, low-noise 3.3 V/1.8 V/1.2 V rails - emphasizing thermal robustness, minimal external components, and wide-temperature operation.

FAQ

What is the minimum input voltage required for stable 3.3 V output at 1 A load?

The LD1117AS33TR requires a minimum input voltage of 4.45 V to maintain regulation at 1 A load, calculated from its 1.15 V typical dropout voltage (3.3 V + 1.15 V). At elevated temperatures or worst-case process corners, the maximum dropout may reach 1.30 V, so 4.6 V headroom is recommended for robust design margin.

Can LD1117AS33TR be used with ceramic output capacitors?

Yes - the LD1117AS33TR is stable with 10 µF ceramic capacitors (X5R/X7R) as specified in the datasheet. Unlike older LDOs, it does not require ESR-based damping; however, ensure the capacitor's DC bias derating maintains ≥10 µF effective capacitance at 3.3 V bias to preserve phase margin and transient response.

How does the thermal pad connection affect performance?

The SOT-223 thermal pad is internally connected to V_OUT, so it must be soldered to a dedicated 3.3 V copper pour with multiple thermal vias to inner ground planes. This connection reduces R_thJA by up to 30 °C/W and prevents thermal shutdown during sustained 1 A operation - floating or grounding the pad degrades thermal performance and risks instability.

Is LD1117AS33TR qualified for automotive applications?

No - LD1117AS33TR is not AEC-Q100 qualified and is specified for industrial temperature range (0 °C to 125 °C junction), not automotive (-40 °C to 150 °C). While it operates within body electronics ambient ranges, ST offers the AEC-Q100 qualified LD1117AV33 (TO-220) and LD1117ADT33TR (DPAK) for automotive-grade deployment.