RF5110G_15 Datasheet, PDF (9/24 Pages) RF Micro Devices – GENERAL PURPOSE / GSM POWER AMPLIFIER

RF5110G
The RF OUT pin provides the output power. Bias for the final stage is fed to this output line, and the feed must be capable of
supporting the approximately 2A of current required. Care should be taken to keep the losses low in the bias feed and output
components. A narrow microstrip line is recommended because DC losses in a bias choke will degrade efficiency and power.
While the part is safe under CW operation, maximum power and reliability will be achieved under pulsed conditions. The data
shown in this data sheet is based on a 12.5% duty cycle and a 600s pulse, unless specified otherwise.
The part will operate over a 3.0V to 5.0V range. Under nominal conditions, the power at 3.5V will be greater than +34.5dBm at
+90°C. As the voltage is increased, however, the output power will increase. Thus, in a system design, the ALC (Automatic
Level Control) Loop will back down the power to the desired level. This must occur during operation, or the device may be dam-
aged from too much power dissipation. At 5.0V, over +38dBm may be produced; however, this level of power is not recom-
mended, and can cause damage to the device.
The HBT breakdown voltage is >20V, so there are no issue with overvoltage. However, under worst-case conditions, with the RF
drive at full power during transmit, and the output VSWR extremely high, a low load impedance at the collector of the output
transistors can cause currents much higher than normal. Due to the bipolar nature of the devices, there is no limitation on the
amount of current de device will sink, and the safe current densities could be exceeded.
High current conditions are potentially dangerous to any RF device. High currents lead to high channel temperatures and may
force early failures. The RF5110G includes temperature compensation circuits in the bias network to stabilize the RF transis-
tors, thus limiting the current through the amplifier and protecting the devices from damage. The same mechanism works to
compensate the currents due to ambient temperature variations.
To avoid excessively high currents it is important to control the V_APC when operating at supply voltages higher than 4.0V, such
that the maximum output power is not exceeded.
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