Microchip Technology UM4901D

Overview

UM4901D 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 typical series resistance at 100 MHz, >5 µs carrier lifetime, and low 3 pF capacitance at 100 V reverse bias-enabling precise RF control in high-power phase shifters and duplexers.

For engineers reviewing the UM4901D datasheet, UM4901D pinout, UM4901D application, or UM4901D equivalent, key selection criteria include thermal path efficiency (shorter than UM4000 series), reverse voltage capability, RF power handling up to 100 kW pulsed, and compatibility with automatic insertion equipment in surface-mount or stud-mounted configurations.

Technical Context

The UM4901D operates as a current-controlled RF resistor with long minority-carrier lifetime (>5 µs) and thick intrinsic region, enabling high RF signal control with low DC bias current. Its non-cavity package design minimizes parasitic inductance and supports stable performance under megawatt-peak RF stress.

Thermally matched configuration and shorter thermal path between chip and package allow UM4901D to achieve higher continuous power ratings than UM4001D-37.5 W at 25°C stud temperature versus 25 W-while maintaining identical electrical characteristics including 200 V reverse voltage and sub-0.5 Ω series resistance at 100 MHz.

Key Specifications

Pinout & Package

UM4901D is housed in Style "D" isolated stud-mount package: anodized aluminum body with insulated mounting stud, solderable cathode terminal, and axial anode lead. Thermal path optimized for direct stud-to-heatsink coupling.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UM4001D, UM4901D delivers +50% continuous power capacity without altering RF linearity or switching speed; compared with UMX4901D, it shares all performance metrics but uses Sn/Pb finish-making UM4901D optimal for legacy rework or non-RoHS environments where solder joint reliability under thermal cycling is prioritized.

Availability

UM4901D is available at Aetrix Electronics and suitable for high-power RF switches, radar duplexers, and UHF phase shifters requiring stable component supply across extended production lifecycles and demanding thermal environments.

Supply support for UM4901D 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) specializes in high-reliability analog and RF semiconductors for aerospace, defense, and communications infrastructure.

The UM4900 series was engineered specifically for high-power microwave switching and attenuation in mission-critical radar, SATCOM, and electronic warfare systems where thermal resilience and RF linearity are non-negotiable.

FAQ

What is the maximum continuous power dissipation for UM4901D?

The UM4901D has a maximum continuous power dissipation of 37.5 W when mounted on a heatsink at 25°C stud temperature. This rating reflects its optimized thermal path versus the UM4001D series. Derating is required above 25°C per the published thermal impedance curve. The UM4901D must be used with proper thermal interface material and mechanical mounting torque to maintain this rating in actual deployment.

Does UM4901D support RoHS-compliant assembly?

Standard UM4901D uses Sn/Pb finish and is not RoHS compliant. For RoHS compliance, specify UMX4901D-the exact same device with matte tin plating meeting EU Directive 2002/95/EC. Electrical, thermal, and RF performance are identical between UM4901D and UMX4901D; only the finish differs.

What is the typical series resistance of UM4901D at RF frequencies?

The UM4901D exhibits a typical series resistance of 0.5 Ω at 100 MHz under 100 mA forward bias. This value remains stable across HF–S-band frequencies due to its long carrier lifetime and thick I-region design. Lower RS directly reduces insertion loss in RF switch and attenuator applications, making UM4901D suitable for high-efficiency signal routing.

Can UM4901D replace UM4001D in existing designs without modification?

UM4901D is mechanically and electrically pin-compatible with UM4001D in Style "D" packaging and can be substituted directly. However, its higher 37.5 W power rating may alter thermal management requirements-verify heatsink adequacy and junction temperature margins. No PCB layout or bias network changes are needed, but system-level thermal validation is recommended after substitution.

What RF frequency range is UM4901D validated for?

UM4901D is characterized and qualified for operation from HF through S-band (3–4 GHz), with verified performance in 100 kW pulsed duplexers and high-power UHF phase shifters. Graphs in the official datasheet confirm stable Rs, Ct, and Rp behavior up to 3 GHz. Performance beyond 4 GHz is not specified and requires application-specific validation.