STMicroelectronics SD2903

Overview

SD2903 from STMicroelectronics is a gold-metallized N-channel MOSFET RF power transistor designed for large-signal amplification in HF/VHF/UHF bands (2–500 MHz) at 28 V DC supply, delivering 30 W output power with ≥13 dB gain and 45–50% drain efficiency at 400 MHz under Class A/AB operation in common-source configuration.

For engineers reviewing the SD2903 datasheet, SD2903 pinout, SD2903 application, or SD2903 equivalent, this device is selected for high-reliability RF final-stage amplifiers where thermal stability, VSWR tolerance (5:1), and consistent gain across temperature are critical design requirements.

Technical Context

The SD2903 operates as a single-ended common-source amplifier with gate-controlled transconductance (gFS = 0.6 mho) and optimized input/output impedance matching (ZIN = 4.6 − j12 Ω, ZDL = 13.6 + j10 Ω at 400 MHz). Its gold metallization ensures stable interconnect performance under RF stress and thermal cycling.

Designed for fixed-bias or self-bias Class A/AB operation, it supports 100 mA quiescent drain current (IDQ) and withstands 65 V drain-source breakdown voltage, enabling robust operation in mismatched load conditions up to 5:1 VSWR without failure.

Key Specifications

Pinout & Package

SD2903 uses the M229 hermetically sealed 4-lead flatpack package (230 × 360 mil, flanged), with dual-drain configuration for improved thermal conduction and current sharing. The case serves as the RF ground reference and primary heat path.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar RF power amplifier applications.

Compared with MRF454 and BLF278, the SD2903 offers superior thermal resistance (1.75 °C/W vs ≥2.5 °C/W) and hermetic reliability in harsh environments, but requires careful gate drive isolation due to parallel-gate layout.

Availability

SD2903 is available at Aetrix Electronics and suitable for HF/VHF/UHF transmitter final stages, land mobile repeaters, and avionics communication amplifiers requiring stable component supply and long-term obsolescence management.

Supply support for SD2903 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, specializing in power management, analog, and RF solutions for industrial, automotive, and communications markets.

The SD2903 belongs to ST's legacy RF power transistor family, engineered specifically for high-reliability, high-efficiency linear amplification in mission-critical HF/VHF/UHF transmitters where thermal stability and load mismatch resilience are non-negotiable.

FAQ

What is the recommended gate bias voltage for Class AB operation at 400 MHz?

The SD2903 achieves optimal linearity and efficiency at IDQ = 100 mA with VGS ≈ 3.2–3.8 V (measured at Tc = 25°C). Gate voltage must be stabilized using low-thermal-drift resistors and bypassed with RF chokes and ceramic capacitors to prevent oscillation.

Can SD2903 be used in push-pull configuration?

Yes - the dual-drain, dual-gate layout and matched internal die structure support push-pull operation. External balancing components (gate resistors, emitter degeneration, and symmetrical layout) are required to maintain amplitude/phase balance and suppress even-order harmonics.

What heatsink interface material meets the Rth(c-s) = 0.40 °C/W specification?

Dow Corning 340 thermal compound-or equivalent silicone-based grease with 0.8–1.2 W/m·K conductivity-is validated for use with flat aluminum or copper heatsinks. Surface finish ≤ 1.6 µm Ra and mounting pressure ≥ 25 psi are required to achieve the specified Rth(c-s).

Is SD2903 still in active production?

No - SD2903 is marked "Obsolete Product(s)" in the official STMicroelectronics datasheet (Rev. November 1999). Aetrix Electronics maintains limited legacy stock with full traceability and provides engineering support for redesign alternatives including BLF278 and MRF454.