onsemi RC1117S33T

Overview

RC1117S33T from Fairchild Semiconductor is a fixed-output 3.3V, 1A low-dropout linear regulator in SOT-223 package, featuring 1.2V typical dropout at 1A, ±2% output voltage accuracy, and on-chip thermal shutdown. It serves as a post-regulator for switching supplies and motherboard clock supply in embedded power systems.

For engineers reviewing the RC1117S33T datasheet, pinout, applications, or equivalent options, key selection criteria include dropout voltage under full load, thermal resistance (Θ_JA = 30°C/W with 0.5 in² copper), load regulation (0.05% typ), and compatibility with 4.8V–7V input range for stable 3.3V rail generation.

Technical Context

The RC1117S33T uses a PNP-based pass transistor architecture where quiescent current flows into the load-unlike traditional PNP regulators-improving efficiency. Its trimmed current limit ensures 1.1–1.5A short-circuit protection while maintaining 1A rated output.

Thermal regulation is enforced via on-chip junction temperature sensing (trip at 155°C with 10°C hysteresis), and ripple rejection reaches 72dB at 120Hz with 22µF tantalum output capacitance-critical for noise-sensitive clock and analog subsystems.

Key Specifications

Pinout & Package

RC1117S33T is housed in a 4-lead plastic SOT-223 package with exposed tab electrically connected to V_OUT for thermal conduction. The package requires soldering to ≥0.5 in² copper area over ground plane for specified Θ_JA.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar low-dropout linear regulator applications.

Compared with TLV1117-33CDCR and AP1117SG-33, RC1117S33T offers superior dropout voltage (1.2V @ 1A) and ripple rejection (72dB), making it optimal for noise-critical 3.3V rails where input headroom is constrained and upstream switching noise is high.

Availability

RC1117S33T is available at Aetrix Electronics and suitable for motherboard clock supplies, active SCSI terminators, and post-regulation of switching supplies requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for RC1117S33T 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

Fairchild Semiconductor was a U.S.-based semiconductor company specializing in power management, analog, and discrete components before its acquisition by ON Semiconductor in 2016.

The RC1117 series was designed specifically for low-voltage, high-efficiency linear regulation in space-constrained systems-targeting applications like SCSI termination, clock distribution, and post-regulation where transient response and minimal input overhead are critical.

FAQ

What is the maximum input voltage for RC1117S33T?

The absolute maximum input voltage for RC1117S33T is 7.5V, but the recommended operating range is 4.8V to 7V to guarantee 3.3V output accuracy and thermal stability. Exceeding 7V risks violating safe operating area limits, especially at high ambient temperatures or full load.

Does RC1117S33T require an external resistor divider for 3.3V output?

No-RC1117S33T is a fixed-output variant; its 3.3V regulation is factory-trimmed and does not require external resistors. The ADJ/GND pin (Pin 1) is internally connected to ground and must be tied to system GND; it is not used for adjustment in this version.

What thermal performance can be expected from RC1117S33T in SOT-223?

With proper PCB layout-specifically a 0.5 in² copper pad connected to the exposed tab-RC1117S33T achieves Θ_JA ≈ 30°C/W. Without adequate copper, Θ_JA may exceed 50°C/W, risking thermal shutdown above ~0.6A at 70°C ambient.

Is RC1117S33T compatible with ceramic output capacitors?

Yes-RC1117S33T is stable with low-ESR ceramic capacitors. The datasheet validates operation with a 10µF ceramic input cap and 22µF tantalum output cap, and no minimum ESR requirement means X5R/X7R ceramics (≥10µF) are fully acceptable and commonly used for size and reliability benefits.

How does RC1117S33T handle short-circuit conditions?

RC1117S33T features trimmed current limiting (1.1–1.5A) and thermal shutdown (155°C trip, 10°C hysteresis). Under sustained short-circuit, it enters current-limit mode first, then shuts down if junction temperature exceeds 155°C-restarting automatically once cooled below 145°C.