Specifications and information are subject to change without notice.

2003-11

Sumitomo Electric Industries, Ltd. 1,Taya-cho, Sakae-ku, Yokohama, 244-8588 Japan

Phone: +81-45-853-7263 Fax: +81-45-853-1291

-9-

Technical Note

P0120003P

800mW GaAs Power FET (Pb-Free Type)

SUMITOMO ELECTRIC

♦Caution: Power Supply Sequence

P0110003P

P0120003P

Application

Circuit

R4

Q1a

GND

R2

Vgs

+6V

Vds

R1

-5V

R3

R5

Q1b

GND

For safe operation, electric power should be supplied in

following sequence. First, the negative voltage should be

applied on the gate, and the voltage should be more negative

than the pinch-off voltage when you turn on the power

supply. Then, drain bias can be applied. Finally, you can turn

on the RF signal.

When turning off the power supply, the sequence should be

(1)RF signal (2)Drain (3)Gate.

Gate

Voltage

0V

Bias Voltage

Drain

Voltage

On

On

0V

More Than 1mS

Off

Bias Voltage

More Than 1mS

Off

Gate

Voltage

0V

Bias Voltage

Drain

Voltage

On

On

0V

More Than 1mS

Off

Bias Voltage

More Than 1mS

Off

Gate

Voltage

0V

Bias Voltage

Drain

Voltage

On

On

0V

More Than 1mS

Off

Bias Voltage

More Than 1mS

Off

Vds

+5.9V

Ids

220mA

Q1

UMT1N (Rohm)

R1

16Ω 1/10W

R2

1.8kΩ 1/10W

R3

0.22Ω RL series (SUSUMU)

R4

1kΩ 1/10W

R5

1.3kΩ 1/10W

♦Bias Circuit

[Passive Biasing]

If you use a fixed bias circuit, you sometimes need to control

the gate bias to get the same Ids, since the devices have some

margin of pinch-off voltage (Vp) variation depending on the

wafer lots. If you employ a fixed Vgs biasing for your

system, you should closely monitor the drain current,

particularly when new wafer lots are introduced.

If you used Ids other than 220mA, you can calculate the

resistance values as follows:

[Active Biasing]

We recommend using an active bias circuit, which can

eliminate the influence of Vp variation. An example of an

active bias circuit called “current mirror ” is shown below.

Here, two PNP transistors having the minimum variation of

Ibe characteristics are used. These transistors adjust Vgs by

changing Vds automatically. It will realize the constant

current characteristics, regardless of the temperature.

The circuit should be connected directly in line with where

the voltage supplies would be normally connected with the

application circuit. Of course a matching circuit is required,

but it is not shown in this figure.

♦Attention to Heat Radiation

In the layout design of the printed circuit board (PCB) on

which the power FETs are attached, the heat radiation to

minimize the device junction temperature should be taken

into account, since it significantly affects the MTTF and RF

performance. In any environment, the junction temperature

should be lower than the absolute maximum rating during

the device operation and it is recommended that the thermal

design has enough margin.

[Note]

In the measurements of RF performance (Pout vs Pin, etc)

using the application circuit described before, the active bias

circuit herein was not utilized. The application circuits were

biased directly from two power supplies.