MGA-72543-TR1 Avago Technologies US Inc., MGA-72543-TR1 Datasheet - Page 16

• Manufacturer Part Number: MGA-72543-TR1
• Description: IC,Microwave/Millimeter Wave Amplifier,GAAS,SOT-343R,PLASTIC
• Manufacturer: Avago Technologies US Inc.

Specifications of MGA-72543-TR1

• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Controlling the Switch
The state of the MGA-72543 (amplifier or bypass mode)
is controlled by the device current. For device currents
greater than 5 mA, the MGA-72543 functions as an am-
plifier. If the device current is set to zero, the MGA- 72543
is switched into a bypass mode in which the amplifier is
turned off and the signal is routed around the amplifier
with a loss of approximately 2.5 dB.
The bypass state is normally engaged in the presence of
high input levels to prevent distortion of the signal that
might occur in the amplifier. In the bypass state, the input
TOI is very high, typically +39 dBm at 1900 MHz.
The simplest method of placing the MGA-72543 into the
bypass mode is to open-circuit the ground terminals at
Pins 1 and 4. With the ground connection open, the inter-
nal control circuit of the MGA-72543 auto-switches from
the amplifier mode into a bypass state and the device
current drops to near zero. Nominal current in the bypass
state is 2 µA with a maximum of 15 µA.
Figure 9. MGA-72543 Amplifier/Bypass State Switching.
An electronic switch can be used to control states as
shown in Figure 9. The control switch could be imple-
mented with either a discrete transistor or simple IC.
The speed at which the MGA-72543 switches between
states is extremely fast and will normally be limited by the
time constants of external circuit components, such as the
bias circuit and the bypass and blocking capacitors.
The input and output of the MGA-72543 while in the
bypass state are internally matched to 50 É∂. The input
return loss can be further improved at 1900 MHz by
adding a 2.7 to 3.9 nH series inductor added to the input.
This is the same approximate value of inductor that is
used to improve input match when the MGA-72543 is in
the amplifier state.
16
3
1
R
bias
4
2
Bypass Switch
Enable
Thermal Considerations
Good thermal design is always an important consideration
in the reliable use of any device, since the Mean Time To
Failure (MTTF) of semiconductors is inversely proportional
to the operating temperature.
The MGA-72543 is a comparatively low power dissipation
device and, as such, operates at conservative tempera-
tures. When biased at 3 volts and 20 mA for LNA applica-
tions, the power dissipation is 3.0 volts x 20 mA, or 60
mW. The temperature increment from the RFIC channel
to its case is then 0.060 watt x 200°C/watt, or only 12°C.
Subtracting the channel-to-case temperature rise from
the suggested maximum junction temperature of 150°C,
the resulting maximum allowable case temperature is
138°C.
The worst case thermal situation occurs when the MGA-
72543 is operated at its Maximum Operating conditions in
an effort to maximize output power or achieve minimum
distortion. A similar calculation for the Maximum Operat-
ing bias of 4.2 volts and 60 mA yields a maximum allow-
able case temperature of 100°C. This calculation further
assumes the worst case of no RF power being extracted
from the device. When operated in a saturated mode,
both power-added efficiency and the maximum allowable
case temperature will increase.
Note: “Case” temperature for surface mount packages
such as the SOT-343 refers to the interface between the
package pins and the mounting surface, i.e., the tempera-
ture at the PCB mounting pads. The primary heat path
from the RFIC chip to the system heatsink is by means of
conduction through the package leads and ground vias
to the groundplane of the PCB.
PCB Layout and Grounding
When laying out a printed circuit board for the MGA-
72543, several points should be considered. Of primary
concern is the RF bypassing of the ground terminals when
the device is biased using the source resistor method.