Microchip Technology UM4901C

Overview

UM4901C from Microsemi is a high-power RF PIN diode designed for low-distortion switching and attenuation in HF–S-band systems. It features 200 V reverse voltage rating, 37.5 W power dissipation (at stud temperature), 0.5 Ω series resistance at 100 MHz, >5 µs carrier lifetime, and low 3 pF capacitance at 100 V reverse bias-enabling precise RF control in antenna couplers and phase shifters.

For engineers reviewing the UM4901C datasheet, UM4901C pinout, UM4901C application, or UM4901C equivalent, key selection criteria include thermal path efficiency, RF voltage handling beyond reverse bias, carrier lifetime impact on distortion, and compatibility with automatic insertion equipment in high-reliability microwave assemblies.

Technical Context

The UM4901C employs a thick intrinsic (I) region and long minority-carrier lifetime (>5 µs) to sustain high RF current with low DC bias, minimizing intermodulation distortion in transmit/receive switching paths. Its non-cavity package design reduces parasitic inductance while enabling direct stud mounting for efficient heat transfer.

It operates with low capacitance (3 pF @ 100 V, 1 MHz) and high parallel resistance (15 kΩ @ 100 V, 100 MHz), supporting stable impedance matching across HF to S-band. The device is qualified for megawatt-peak-power duplexers and UHF phase shifters, with proven reliability over thousands of operational hours.

Key Specifications

Pinout & Package

UM4901C is housed in a ceramic-metal "Style C" isolated stud package with two terminals: anode and cathode. The stud serves as the cathode connection and provides direct thermal and electrical grounding to heatsink or chassis.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-power RF PIN diode applications.

Compared with UM4001C and UM4901D, the UM4901C offers optimal balance of high thermal capability (37.5 W), standardized Style C mounting, and proven field reliability in cavity-based antenna systems-making it preferred for single-stud, space-constrained UHF/S-band front-ends.

Availability

UM4901C is available at Aetrix Electronics and suitable for antenna couplers, UHF phase shifters, megawatt duplexers, and HF–S-band attenuators requiring stable component supply across military, aerospace, and broadcast RF programs.

Supply support for UM4901C 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

Microsemi (now part of Microchip Technology) is a U.S.-based semiconductor company specializing in high-reliability analog and RF components for defense, aerospace, and communications infrastructure.

The UM4000/UM4900 product line was engineered specifically for high-power RF switching and attenuation in mission-critical radar, EW, and satellite ground station systems-emphasizing thermal robustness, distortion control, and long-term field reliability.

FAQ

What is the maximum continuous power dissipation for UM4901C?

The UM4901C has a maximum continuous power dissipation of 37.5 W when mounted on a heatsink held at 25°C stud temperature. This rating assumes proper thermal interface material and mechanical clamping per Microsemi's Style C mounting guidelines. Derating is required above 25°C stud temperature, following the typical power rating curve shown in Figure 4 of the UM4000/UM4900 datasheet. The UM4901C achieves this higher rating than UM4001C due to its optimized thermal path.

Does UM4901C support RoHS compliance?

Yes, the RoHS-compliant version of UM4901C is available as UMX4901C, featuring a matte tin finish instead of Sn/Pb. UMX4901C meets EU Directive 2002/95/EC requirements and retains identical electrical and thermal specifications as UM4901C. No performance trade-offs are introduced in the RoHS variant, and it is fully compatible with standard reflow and hand-soldering processes used for Style C packages.

What is the typical carrier lifetime of UM4901C and why does it matter?

The UM4901C has a minimum carrier lifetime of 5 µs, with typical values reaching 10 µs at 10 mA forward bias. This long lifetime enables linear RF conduction with low intermodulation distortion-critical in analog attenuators and phase shifters where signal fidelity must be preserved. Shorter lifetimes would increase harmonic generation and reduce dynamic range, especially under high RF drive conditions common in radar and EW systems.

Can UM4901C be used in pulsed RF applications?

Yes, UM4901C is qualified for pulsed RF operation up to 100 kW peak power with 1 µs pulse width. Its robust construction and high reverse voltage rating (200 V) allow it to safely clamp and route RF energy far exceeding the applied DC bias-making it ideal for T/R switching in radar duplexers. Pulse thermal impedance data confirms stable junction temperatures under repetitive short-duration loads, as validated in thousands of operational hours.

What package type is UM4901C and how is it mounted?

UM4901C uses Microsemi's "Style C" isolated stud package-a ceramic-metal hermetic enclosure with a threaded metal stud serving as the cathode and primary thermal interface. It is mounted by bolting the stud directly to a heatsink or chassis using specified torque (typically 10–15 in-lb) and thermal interface material. The anode is accessed via a top-side solderable terminal, enabling both RF and DC connections in compact, high-power layouts.