Microchip Technology UMX9989AP

Overview

UMX9989AP from Microsemi is a dual ultra-low magnetic moment PIN diode module designed for passive RF protection and switching in MRI systems. It features matched anti-parallel diode pairs, ±0.45 V forward voltage at 1 A, 8 pF capacitance at 0 V/1 MHz, <80 µS conductance at 0 V/64 MHz, and operates from –65°C to +150°C. It serves as a limiter for MRI receiver LNAs and enables passive surface coil detuning without driver circuitry.

For engineers reviewing the UMX9989AP datasheet, UMX9989AP pinout, UMX9989AP application, or UMX9989AP equivalent, key selection criteria include ultra-low magnetic construction for MRI compatibility, matched pair symmetry for coil assembly accuracy, low insertion loss in both on/off states, and surface-mount footprint supporting automated placement in medical RF assemblies.

Technical Context

The UMX9989AP integrates two anti-parallel silicon PIN diodes in a single non-cavity, planar passivated package with metallurgical bonding. Its ultra-low magnetic moment avoids image distortion in high-field MRI scanners, while its thermally matched configuration ensures balanced RF conduction during transmitter pulses.

It operates in self-biasing mode: loop current from MRI transmit pulses turns on the diodes to detune surface coils or clamp receiver inputs. No external bias control is required-enabling fully passive, driverless operation in sinc(x)-gated pulse sequences.

Key Specifications

Pinout & Package

UMX9989AP uses a proprietary surface-mount dual-diode module package with two terminals: one common anode/cathode node and one differential pair node. The mechanical outline (Style "UM9989AP") specifies a compact, non-cavity, leadless footprint optimized for minimal parasitic inductance and thermal impedance in MRI RF coils.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar MRI passive diode applications.

Compared with UMX9989A and UM7201SM, the UMX9989AP uniquely delivers factory-matched anti-parallel operation in a single RoHS-compliant SMT package-reducing coil assembly time by >40%, eliminating polarity errors, and ensuring repeatable RF performance across production MRI coil batches without driver components.

Availability

UMX9989AP is available at Aetrix Electronics and suitable for MRI receiver protection, surface coil detuning, and passive blocking circuits requiring stable component supply in medical imaging OEM programs.

Supply support for UMX9989AP 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 semiconductor company specializing in high-reliability analog, RF, and radiation-hardened components for aerospace, defense, and medical applications.

The UMX9989AP belongs to Microsemi's MRI-optimized RF diode product line, engineered specifically to meet ultra-low magnetic moment, thermal symmetry, and passive switching requirements of clinical and research MRI systems.

FAQ

What is the primary function of the UMX9989AP in MRI systems?

The UMX9989AP serves as a dual anti-parallel passive RF switch and limiter in MRI systems. It protects receiver LNAs from high-power transmit pulses and enables passive detuning of surface coils by turning on via induced loop current-without external bias. Its ultra-low magnetic construction prevents image distortion, making it essential for clinical MRI coil designs where field homogeneity is critical. The UMX9989AP achieves this through matched silicon PIN diodes in a non-cavity, planar package.

Does the UMX9989AP require external bias or driver circuitry?

No, the UMX9989AP operates in fully passive mode-no external bias or driver circuitry is needed. It turns on automatically when RF-induced loop current flows through the surface coil during MRI transmit pulses. This self-biasing behavior is enabled by its matched anti-parallel configuration and low forward voltage (±0.45 V). The UMX9989AP is therefore ideal for simplifying coil architecture and improving reliability in MRI hardware where space, heat, and EMI constraints prohibit active drivers.

How does the UMX9989AP differ from standard PIN diodes like the UM7201SM?

The UMX9989AP is a factory-matched dual anti-parallel module designed specifically for MRI passive switching, whereas the UM7201SM is a single high-power PIN diode requiring external bias and driver support. Unlike UM7201SM, the UMX9989AP provides inherent symmetry, ultra-low magnetic content, and zero-bias operation-eliminating polarity errors and reducing assembly labor. The UMX9989AP also features lower parasitic capacitance (8 pF) and optimized thermal matching not found in discrete alternatives.

Is the UMX9989AP RoHS compliant and suitable for medical device manufacturing?

Yes, the UMX9989AP is explicitly marked RoHS compliant in its official documentation and manufactured using lead-free materials compatible with medical device regulatory requirements. Its non-cavity, surface-mount construction supports automated reflow assembly per ISO 13485-aligned processes. The UMX9989AP's ultra-low magnetic moment, wide temperature range (–65°C to +150°C), and tested surge robustness make it qualified for use in Class IIa/IIb MRI accessories and OEM coil assemblies subject to IEC 60601-2-33 compliance.

Can the UMX9989AP be used outside of MRI applications?

The UMX9989AP is engineered exclusively for MRI-grade passive RF protection and detuning, with design priorities including ultra-low magnetic moment, thermal symmetry, and self-biasing behavior under pulsed RF fields. While its electrical parameters (e.g., 8 pF capacitance, ±0.45 V VF) may appear usable in other RF switching contexts, its non-standard package, lack of DC bias terminals, and absence of characterization for non-MRI frequencies or waveforms make it unsuitable for general-purpose RF switching. Use of UMX9989AP outside MRI systems is not supported by Microsemi's specifications or qualification data.