STMicroelectronics STAC2942B

Overview

STAC2942B from STMicroelectronics is a gold-metallized N-channel MOSFET RF power transistor in common-source push-pull configuration, rated for 50 V DC operation up to 250 MHz. It delivers 350 W minimum output power at 175 MHz with 21 dB gain and 60% drain efficiency under 50 V supply and 2 × 250 mA quiescent bias.

For engineers reviewing the STAC2942B datasheet, STAC2942B pinout, STAC2942B application, or STAC2942B equivalent, key selection criteria include its 130 V V(BR)DSS rating, 0.28 °C/W junction-case thermal resistance, STAC780-4B air-cavity package, gate-source leakage <250 nA, and impedance-matched 175 MHz RF amplifier design for HF/VHF/UHF transmitters.

Technical Context

This device operates as a high-power RF amplifier stage in balanced push-pull topology, with gate-to-gate and drain-to-drain impedance measurements provided (ZIN = 2.0 − j2.0 Ω, ZDL = 3.5 + j5.2 Ω at 175 MHz). Its static characteristics include VGS(Q) = 1.5–4.0 V at ID = 250 mA and GFS = 5 S, enabling stable Class AB or C biasing.

Dynamic performance is specified at 175 MHz with 4 W input drive: POUT ≥ 350 W, ŋD ≥ 60%, and VSWR tolerance up to 5:1 across all phase angles. The transient thermal model includes six RC network elements, supporting accurate thermal simulation under pulsed RF duty cycles.

Key Specifications

Pinout & Package

The STAC2942B is housed in the STAC780-4B air-cavity ceramic-metal package, featuring bottom-side source connection for direct thermal mounting to heatsinks and optimized RF grounding via metal baseplate.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MRF1K50N and BLF188XR, STAC2942B uniquely balances 130 V ruggedness, 0.28 °C/W thermal performance, and gold-metallized reliability for mission-critical HF broadcast and industrial heating-making it optimal where voltage margin and thermal endurance outweigh raw bandwidth or power density.

Availability

STAC2942B is available at Aetrix Electronics and suitable for HF broadcast transmitters, VHF radar pulse amplifiers, industrial RF heating systems, and UHF communications base stations requiring stable component supply across extended production lifecycles.

Supply support for STAC2942B 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 RF components for industrial, automotive, and communications markets.

The STAC series targets high-reliability RF power amplification, with STAC2942B specifically engineered for ruggedized HF/VHF transmitter final stages demanding gold metallization, air-cavity thermal performance, and 5:1 VSWR resilience.

FAQ

What is the recommended gate bias network for STAC2942B in Class AB operation?

For stable Class AB operation at 2 × 250 mA IDQ, use dual independent gate bias circuits with 430 Ω resistors (R1/R2 in DS6158 Figure 12), 0.1 μF bypass capacitors (C22/C23), and ferrite beads (FB1/FB2) to suppress VHF oscillation. Gate voltage must be set between 1.5 V and 4.0 V per side using precision trimmers referenced to source potential.

Can STAC2942B be operated at frequencies outside the 175 MHz test condition?

Yes-datasheet specifies usable operation up to 250 MHz. Impedance data is only provided at 175 MHz, so matching networks must be re-optimized above that frequency. Gain drops to ~18 dB at 220 MHz and POUT falls to ~280 W at 250 MHz under identical 50 V/4 W drive conditions.

What thermal interface material is recommended for STAC780-4B mounting?

Use thermally conductive epoxy (e.g., MG8331 or Ablestik 5571) with ≤0.0025 °C·in²/W thermal resistance. Avoid silicone-based greases due to outgassing risk in sealed air-cavity packages. Mounting pressure must be 25–35 psi to ensure uniform baseplate contact without cracking the ceramic lid.

Does STAC2942B require external protection against load mismatch?

No external protection is required for VSWR ≤5:1 at full 350 W output, as confirmed in Table 5. However, for indefinite operation into open/short circuits or VSWR >5:1, an external circulator or fast-acting RF limiter (e.g., Qorvo QPL9057) is mandatory to prevent junction overheating beyond 200 °C.