MRF275G_15 Datasheet, PDF (18/19 Pages) M/A-COM Technology Solutions, Inc. – The RF MOSFET Line

MRF275G
The RF MOSFET Line
150W, 500MHz, 28V
Gate Termination — The gates of this device are essen-
tially capacitors. Circuits that leave the gate open–circuited
or floating should be avoided. These conditions can result in
turn–on of the devices due to voltage build–up on the input
capacitor due to leakage currents or pickup.
Gate Protection — These devices do not have an inter-
nalmonolithic zener diode from gate–to–source. If gate pro-
tection is required, an external zener diode is recommended.
Using a resistor to keep the gate–to–source impedance low
also helps damp transients and serves another important
function. Voltage transients on the drain can be coupled to
the gate through the parasitic gate–drain capacitance. If the
gate–to–source impedance and the rate of voltage change
on the drain are both high, then the signal coupled to the
gate may be large enough to exceed the gate–threshold
voltage and turn the device on.
HANDLING CONSIDERATIONS
When shipping, the devices should be transported only in
antistatic bags or conductive foam. Upon removal from the
packaging, careful handling procedures should be adhered
to. Those handling the devices should wear grounding
straps and devices not in the antistatic packaging should be
kept in metal tote bins. MOSFETs should be handled by the
case and not by the leads, and when testing the device, all
leads should make good electrical contact before voltage is
applied. As a final note, when placing the FET into the sys-
tem it is designed for, soldering should be done with
grounded equipment.
DESIGN CONSIDERATIONS
The MRF275G is a RF power N–channel enhancement
M/A-COM Products
Released - Rev. 07.07
mode field–effect transistor (FETs) designed for HF, VHF
and UHF power amplifier applications. M/A-COM RF MOS-
FETs feature a vertical structure with a planar design. M/A-
COM Application Note AN211A, FETs in Theory and Prac-
tice, is suggested reading for those not familiar with the con-
struction and characteristics of FETs. The major advantages
of RF power FETs include high gain, low noise, simple bias
systems, relative immunity from thermal runaway, and the
ability to withstand severely mismatched loads without suf-
fering damage. Power output can be varied over a wide
range with a low power dc control signal.
DC BIAS
The MRF275G is an enhancement mode FET and, there-
fore, does not conduct when drain voltage is applied. Drain
current flows when a positive voltage is applied to the gate.
RF power FETs require forward bias for optimum perform-
ance. The value of quiescent drain current (IDQ) is not criti-
cal for many applications. The MRF275G was characterized
at IDQ = 100 mA, each side, which is the suggested mini-
mum value of IDQ. For special applications such as linear
amplification, IDQ may have to be selected to optimize the
critical parameters. The gate is a dc open circuit and draws
no current. Therefore, the gate bias circuit may be just a
simple resistive divider network. Some applications may
require a more elaborate bias system.
GAIN CONTROL
Power output of the MRF275G may be controlled from its
rated value down to zero (negative gain) by varying the dc
gate voltage. This feature facilitates the design of manual
gain control, AGC/ALC and modulation systems.
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and/or prototype measurements. Commitment to develop is not guaranteed.
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Solutions has under development. Performance is based on engineering tests. Specifications are
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typical. Mechanical outline has been fixed. Engineering samples and/or test data may be available. _{M/A-COM Technology Solutions Inc. and its affiliates reserve the right to make}
Commitment to produce in volume is not guaranteed.
changes to the product(s) or information contained herein without notice.