The RF MOSFET Line
100W, 400MHz, 28V
Rev. V1
MRF175LU
1
1
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Product Image
Designed for broadband commercial and military applications using single
ended circuits at frequencies to 400 MHz. The high power, high gain and
broadband performance of each device makes possible solid state trans-
mitters for FM broadcast or TV channel frequency bands.
N-Channel enhancement mode
ï‚· Guaranteed performance
 MRF175LU @ 28 V, 400 MHz (―U‖ Suffix)
Output power — 100 W
Power gain — 10 dB typ
Efficiency — 55% typ
ï‚· 100% ruggedness tested at rated output power
ï‚· Low thermal resistance
 Low Crss — 20 pF Typ @ VDS = 28 V
CASE 333–04, STYLE 2
The RF MOSFET Line
100W, 400MHz, 28V
Rev. V1
MRF175LU
2
2
M/A-COM Technology Solutions Inc. (MACOM) and its affiliates reserve the right to make changes to the product(s) or information contained herein without notice.
Visit www.macom.com for additional data sheets and product information.
For further information and support please visit:
https://www.macom.com/support
2
The RF MOSFET Line
100W, 400MHz, 28V
Rev. V1
MRF175LU
3
3
M/A-COM Technology Solutions Inc. (MACOM) and its affiliates reserve the right to make changes to the product(s) or information contained herein without notice.
Visit www.macom.com for additional data sheets and product information.
For further information and support please visit:
https://www.macom.com/support
3
The RF MOSFET Line
100W, 400MHz, 28V
Rev. V1
MRF175LU
4
4
M/A-COM Technology Solutions Inc. (MACOM) and its affiliates reserve the right to make changes to the product(s) or information contained herein without notice.
Visit www.macom.com for additional data sheets and product information.
For further information and support please visit:
https://www.macom.com/support
4
The RF MOSFET Line
100W, 400MHz, 28V
Rev. V1
MRF175LU
5
5
M/A-COM Technology Solutions Inc. (MACOM) and its affiliates reserve the right to make changes to the product(s) or information contained herein without notice.
Visit www.macom.com for additional data sheets and product information.
For further information and support please visit:
https://www.macom.com/support
5
The RF MOSFET Line
100W, 400MHz, 28V
Rev. V1
MRF175LU
6
6
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MOSFET CAPACITANCES
The physical structure of a MOSFET results in capacitors
between the terminals. The metal oxide gate structure de-
termines the capacitors from gate–to–drain (Cgd), and gate–
to–source (Cgs). The PN junction formed during the fabrica-
tion of the MOSFET results in a junction capacitance from
drain–to–source (Cds).
These capacitances are characterized as input (Ciss),
output (Coss) and reverse transfer (Crss) capacitances on
data sheets. The relationships between the inter–terminal
capacitances and those given on data sheets are shown
below. The Ciss can be specified in two ways:
1. Drain shorted to source and positive voltage at the
gate.
2. Positive voltage of the drain in respect to source
and zerovolts at the gate. In the latter case the
numbers are lower. However, neither method
represents the actual operating conditions in RF
applications.
The Ciss givenin the electrical characteristics table was
measured using method 2 above. It should be noted that-
Ciss, Coss, Crss are measured at zero drain current and are
provided for general information about the device. They are
not RF design parameters and no attempt should be made
to use them as such.
LINEARITY AND GAIN CHARACTERISTICS
In addition to the typical IMD and power gain, data pre-
sented in Figure 3 may give the designer additional infor-
mation on the capabilities of this device. The graph repre-
sents the small signal unity current gain frequency at a
given drain current level. This is equivalent to fT for bipolar
transistors. Since this test is performed at a fast sweep
speed, heating of the device does not occur. Thus, in nor-
mal use, the higher temperatures may degrade these char-
acteristics to some extent.
DRAIN CHARACTERISTICS
One figure of merit for a FET is its static resistance in the
full–on condition. This on–resistance, VDS(on), occurs in the
linear region of the output characteristic and is specified un-
der specific test conditions for gate–source voltage and drain
current. For MOSFETs, VDS(on) has a positive temperature
coefficient and constitutes an important design consideration
at high temperatures, because it contributes to the power
dissipation within the device.
GATE CHARACTERISTICS
The gate of the MOSFET is a polysilicon material, and is
electrically isolated from the source by a layer of oxide. The
input resistance is very high — on the order of 109 ohms —
resulting in a leakage current of a few nanoamperes. Gate
control is achieved by applying a positive voltage slightly in
excess of the gate–to–source threshold voltage, VGS(th).
Gate Voltage Rating — Never exceed the gate voltage rat-
ing (or any of the maximum ratings on the front page). Ex-
ceeding the rated VGS can result in permanent damage to
the oxide layer in the gate region.
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 internal
monolithic zener diode from gate–to–source. If gate protec-
tion 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 MRF175L is a RF power N–channel enhancement
mode field–effect transistor (FETs) designed for HF, VHF
andUHF power amplifier applications. M/A-COM RF MOS-
FETs feature a vertical structure with a planar design. M/A-
RF POWER MOSFET CONSIDERATIONS
The RF MOSFET Line
100W, 400MHz, 28V
Rev. V1
MRF175LU
7
7
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Visit www.macom.com for additional data sheets and product information.
For further information and support please visit:
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7
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 mis-
matched loads without suffering damage. Power output can
be varied over a wide range with a low power dc control sig-
nal.
DC BIAS
The MRF175L 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 critical
for many applications. The MRF175L was characterized at
IDQ = 100 mA, each side, which is the suggested minimum-
value of IDQ. For special applications such as linear amplifi-
cation, IDQ may have to be selected to optimize the critical
parameters. The gate is a dc open circuit and draws no cur-
rent. 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 MRF175L 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.
The RF MOSFET Line
100W, 400MHz, 28V
Rev. V1
MRF175LU
8
8
M/A-COM Technology Solutions Inc. (MACOM) and its affiliates reserve the right to make changes to the product(s) or information contained herein without notice.
Visit www.macom.com for additional data sheets and product information.
For further information and support please visit:
https://www.macom.com/support
8
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