Microchip Technology UM4902D

Overview

UM4902D from Microsemi is a high-power RF PIN diode designed for low-distortion switching and attenuation in HF–S-band systems. It features 400 V reverse voltage rating, 37.5 W power dissipation (at 25°C stud temperature), 0.5 Ω typical series resistance at 100 MHz, >5 µs carrier lifetime, and 3 pF capacitance at 100 V reverse bias. It is used in UHF phase shifters and megawatt peak-power duplexers.

For engineers reviewing the UM4902D datasheet, UM4902D pinout, UM4902D application, or UM4902D equivalent, key selection criteria include thermal path efficiency (shorter than UM4000 series), RF voltage handling beyond applied reverse bias, low-conductance/low-capacitance behavior at 0 V, and compatibility with automatic insertion equipment in high-reliability RF front-end assemblies.

Technical Context

The UM4902D employs a non-cavity, thermally matched PIN structure with a thick intrinsic region enabling long minority-carrier lifetime (>5 µs) and high charge storage. Its design supports high RF signal control with low DC bias current while maintaining low distortion across HF to S-band frequencies.

It operates as a voltage-controlled RF resistor in forward bias and a low-loss RF capacitor in reverse bias. The UM4902D's shorter thermal path-relative to UM4000-series counterparts-enables higher continuous power dissipation (37.5 W at 25°C stud temp) without derating, critical for pulsed and CW high-power RF switching.

Key Specifications

Pinout & Package

UM4902D is housed in Style "D" isolated stud-mount package: copper-tungsten base with solderable anode/cathode terminals, insulated mounting stud, and non-cavity construction for stable RF performance. Thermal path from chip to stud is optimized for lower junction-to-case resistance vs. UM4000 series.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UM4002D and MADP-000907, UM4902D delivers superior thermal performance in stud-mounted configurations, enabling higher average power handling and longer operational life in mission-critical UHF/S-band systems where thermal management and pulse robustness are decisive.

Availability

UM4902D is available at Aetrix Electronics and suitable for UHF phase shifters, megawatt peak-power duplexers, antenna selector networks, and RF cavity tuning applications requiring stable component supply across extended production lifecycles.

Supply support for UM4902D 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 aerospace, defense, and industrial markets.

The UM4900 series was developed specifically for high-power RF switching and attenuation in radar, EW, and communications systems where thermal robustness, low distortion, and proven field reliability are mandatory.

FAQ

What is the maximum continuous power dissipation for UM4902D?

The UM4902D has a maximum power dissipation of 37.5 W at 25°C stud temperature. This rating reflects its optimized thermal path versus the UM4000 series. Derating is required above 25°C per the typical power rating curve on page 4 of the datasheet. For pulsed operation, thermal impedance curves support 100 kW peak power at 1 µs pulse width.

Does UM4902D have RoHS-compliant variants?

Yes - RoHS-compliant versions of UM4902D are available as UMX4902D, featuring a matte tin finish per EU Directive 2002/95/EC. The UMX prefix denotes full RoHS compliance, including lead-free terminations and packaging. Electrical and thermal specifications remain identical to the standard UM4902D.

What is the typical series resistance of UM4902D at RF frequencies?

The UM4902D exhibits a typical series resistance of 0.5 Ω at 100 MHz under 100 mA forward bias. Measured values range from 0.3 Ω (min) to 0.5 Ω (typ), directly impacting insertion loss in RF switch and attenuator designs. Lower R_S contributes to higher power-handling capability and reduced self-heating during RF conduction.

How does UM4902D differ from UM4002D in thermal performance?

UM4902D achieves higher power dissipation (37.5 W vs. 25 W) due to a shorter thermal path between the silicon die and the mounting stud. This results in lower thermal resistance (θ = 4°C/W vs. 6°C/W for UM4002D under Condition C), enabling more efficient heat extraction in high-duty-cycle RF applications such as active phased arrays.

Is UM4902D suitable for use in S-band (2–4 GHz) applications?

Yes - UM4902D is qualified for operation through S-band, supported by measured data showing stable C_T, R_S, and R_P up to 3 GHz. Its >5 µs carrier lifetime and low capacitance (3 pF) ensure low distortion and predictable impedance behavior in S-band switches, attenuators, and phase shifters used in radar and SATCOM systems.