UMX9989AP/TR

Overview

The UMX9989AP/TR is a dual ultra-low magnetic moment fast diode module designed for MRI applications. It integrates two matched anti-parallel diodes in a surface mount package to optimize performance and reduce assembly labor. The device acts as a passive protector for MRI receiver LNAs against high RF energy fields, including long pulses and spikes. Key electrical parameters at 25°C include a forward voltage of ±0.38 V typical at IF = 10 µA and ±1.2 V typical at IF = 1 A. Capacitance is typically 4 pF at VR = 0 V and F = 1 MHz, and 8 pF at 64 MHz. Conductance is 80 µS at 64 MHz, with a parallel resistance of 12 kOhms. Operating temperature ranges from -65°C to +150°C.

Feature Summary

• Ultra-low magnetic construction suitable for sensitive MRI environments
• Matched pairs ensure correct polarity insertion with minimum parasitic inductance
• Surface mount package compatible with automatic insertion equipment
• Metallurgical bond and planar passivated chip for reliability

Applications

• MRI receiver protection from high RF energy fields
• Passive switching of surface coil detuning circuits
• Passive blocking circuits for MRI systems
• Implementation of semi-active detune designs when combined with PIN diodes

Procurement Notes

Verify the specific suffix TR indicates tape and reel packaging configuration by consulting the manufacturer's official documentation or distributor specifications. Confirm RoHS compliance status and current availability directly with Microchip Technology or authorized suppliers, as manufacturing sources may have changed following corporate acquisitions. Ensure ordering requirements align with the latest factory specifications.

Selection Notes

Select this component for MRI applications requiring ultra-low magnetic moment characteristics to prevent interference with imaging quality. The dual anti-parallel configuration simplifies coil design by eliminating polarity errors and reducing parasitic elements. Consider combining with UM7201SM PIN diodes for semi-active detuning implementations that require higher power switching capabilities during transmitter sidelobes.

Part Context

The UMX9989AP is part of Microsemi's (now Microchip) specialized line of MRI protection diodes. It represents an evolution from single diode solutions like the UM9989, offering integrated dual functionality in a compact surface mount package. This integration reduces assembly complexity and improves consistency in MRI coil manufacturing compared to discrete component implementations.

Replacement Considerations

Direct replacements are not explicitly listed in the provided datasheet. Evaluate similar ultra-low magnetic moment diodes from Microchip or other manufacturers specializing in MRI components. Verify magnetic properties, capacitance values, and package compatibility before substitution.