UMX9989AP_09 Datasheet, PDF (1/3 Pages) Microsemi Corporation – DUAL ULTRA LOW MAGNETIC MOMENT FAST DIODES FOR MRI APPLICATIONS

UMX9989AP™
DUAL ULTRA LOW MAGNETIC MOMENT
FAST DIODES FOR MRI APPLICATIONS
RoHS compliant
DESCRIPTION
The UMX9989AP is the first MRI switching diode module, designed to optimize
performance and reduce assembly labor, cost, and polarity errors.
There are two principle applications for which the UMX9989AP modules are
intended:
1) MRI receiver protection from high RF energy fields, including long RF pulses
and RF spike pulses present in most MRI machines. The UMX9989AP acts as a
passive protector (limiter) for the MRI receiver’s LNA. The diode assembly
exhibits extremely low insertion loss, both in the “on” state (high power present)
and the “off” state (receiver power present) so the Receiver’s Noise Figure is not
increased by the protector circuit.
2) Passive switching of surface coil detuning and blocking circuits. In this case, the
flow of loop current during transmitter pulse turns on the diodes, without a switch
driver.
If the UMX9989AP is combined with a PIN diode (UM7201SM) the combination
can be used to implement a semi-active detune or block circuit design. The
UMX9989AP’s turn on the PIN diode (used for higher power switching) during
the sinc(x) sidelobes, before the main pulse of the transmitter waveform, sinc(x) =
[sin (x)]/x, occurs. The mechanical drawing shows the structure of the diode pair.
Manufacture of dual anti-parallel pairs of UMX9989’s ensures that the matched
pair of diodes can be inserted in a coil with the correct diode polarities and with the
minimum parasitic inductance and capacitance, thermal impedance and labor for
the coil manufacturer.
IMPORTANT:
For the most current data, consult our website: www.MICROSEMI.com
ABSOLUTE MAXIMUM RATINGS AT 25º C
(UNLESS OTHERWISE SPECIFIED)
Rating
Symbol
Value
Unit
Non-Repetitive Peak Forward Surge Current
8.3ms Single half sine wave
I_FSM
2
A
Storage Temperature
T stg -65 to +150
ºC
Operating Temperature
T op -65 to +150
ºC
KEY FEATURES
 Ultra low magnetic construction
 RoHS compliant
 Matched pairs available
 Surface mount package.
 Metallurgical bond
 Planar passivated chip
 Non cavity design
 Thermally matched configuration
 Low capacitance at 0 V bias
 Low conductance at 0 V bias
 Compatible with automatic
insertion equipment
APPLICATIONS/BENEFITS
 MR passive receiver protection
 MR passive blocking circuits
 MR passive detuning circuits
 MR passive disable circuits
Copyright  2007
Rev: 2009-01-19
Microsemi
Microwave Products
75 Technology Drive, Lowell, MA. 01851, 978-442-5600, Fax: [phone]
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