Microchip Technology UM4901A

Overview

UM4901A 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 (Style C), 0.5 Ω typical series resistance at 100 MHz, >5 µs carrier lifetime, and low 2.4–3 pF capacitance at 100 V reverse bias-enabling precise RF control in high-power phase shifters and duplexers.

For engineers reviewing the UM4901A datasheet, UM4901A pinout, UM4901A application, or UM4901A equivalent, key selection criteria include thermal path efficiency (shorter than UM4000 series), reverse voltage tolerance, RF power handling up to 100 kW pulsed, and compatibility with automatic insertion equipment in high-reliability microwave subsystems.

Technical Context

The UM4901A is a silicon PIN diode with a thick intrinsic (I) region optimized for high RF power handling and low distortion. Its long carrier lifetime (>5 µs) and low series resistance (0.3–0.5 Ω) support efficient RF current control under modest DC bias, while its low capacitance (2.4–3 pF at 100 V) ensures minimal signal loading in tuned circuits.

Thermally, the UM4901A (Style C) is rated for 37.5 W at 25 °C stud temperature with a thermal resistance of 4 °C/W-significantly lower than the UM4001C (6 °C/W)-due to an engineered shorter thermal path from chip to package stud, enabling higher continuous RF power operation in compact UHF antenna systems.

Key Specifications

Pinout & Package

UM4901A is supplied in Style C package: isolated stud-mount metal-ceramic housing with anode and cathode terminals on opposite sides of the stud. The package provides direct thermal conduction from die to mounting surface and electrical isolation between terminals and stud.

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 UMX4901C, the UM4901A delivers superior thermal performance for continuous high-power operation, while UMX4901C offers identical functionality with mandatory environmental compliance-making UM4901A ideal for legacy thermal designs and UMX4901C for new RoHS-aligned programs.

Availability

UM4901A is available at Aetrix Electronics and suitable for UHF phase shifters, megawatt peak-power duplexers, and antenna selector networks requiring stable component supply across extended production lifecycles and demanding RF reliability standards.

Supply support for UM4901A 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 applications.

The UM4900 series was developed specifically for high-power microwave switching in radar, EW, and SATCOM systems where thermal efficiency, RF linearity, and long-term parameter stability are mission-critical.

FAQ

What is the maximum reverse voltage rating for UM4901A?

The UM4901A has a reverse voltage rating of 200 V at 10 µA leakage current. This rating is verified per Microsemi's absolute maximum ratings table and applies under steady-state DC reverse bias conditions. The device can withstand transient RF peak voltages well in excess of this value due to its thick I-region and long carrier lifetime, making it suitable for high-peak-power S-band switching applications where UM4901A is deployed.

Which package style does UM4901A use, and what are its thermal characteristics?

UM4901A uses Style C packaging: an isolated stud-mount metal-ceramic case with electrically isolated anode and cathode terminals. Its thermal resistance is 4 °C/W from junction to stud at 25 °C, enabling 37.5 W power dissipation-25% higher than the UM4001C variant. This makes UM4901A especially effective in thermally constrained UHF phase shifter modules where UM4901A's shorter thermal path improves reliability.

How does UM4901A differ from UM4001A in terms of RF performance?

UM4901A and UM4001A share identical electrical parameters-including 200 V reverse voltage, 0.5 Ω series resistance, and >5 µs carrier lifetime-but differ thermally: UM4901A achieves 37.5 W dissipation (Style C) versus 25 W for UM4001C due to a shorter thermal path. RF performance is functionally equivalent, but UM4901A supports higher continuous RF power in the same footprint, making UM4901A preferable for high-duty-cycle radar subsystems.

Is UM4901A RoHS compliant, and what is the compliant alternative?

The standard UM4901A is not RoHS compliant; it uses Sn/Pb finish. The RoHS-compliant alternative is UMX4901A, which substitutes matte tin plating while retaining identical electrical, thermal, and mechanical specifications. UMX4901A is drop-in compatible with UM4901A in all applications requiring EU Directive 2002/95/EC compliance, and UM4901A users may migrate to UMX4901A without redesign.

What is the typical capacitance of UM4901A at zero bias, and why does it matter?

UM4901A exhibits low capacitance-2.4–3 pF at 100 V reverse bias and 1 MHz-though zero-bias capacitance is not explicitly specified in the datasheet. Its low capacitance minimizes reactive loading on RF filter and cavity networks during OFF-state operation, preserving impedance matching and reducing insertion loss. This behavior is critical in antenna selector and coupler-switching applications where UM4901A maintains signal integrity across multi-octave bands.