RF3806 Ver la hoja de datos (PDF) - RF Micro Devices

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RF3806

GaAs HBT PRE-DRIVER AMPLIFIER

RF Micro Devices 

RF3806

At POUT=26dBm, see that Tj=160°C for ambient (stage) temperature=85°C. At this condition, temperature of case (GND

slug) is calculated:

TCASE=TREF+PDISS*(RTH_BOARD)=94°C+(6.191W)*1°C/W=100.2°C. Note that TREF was elevated to 94°C when stage was

set at 85°C. Thus, thermal resistance results can be subject to where one defines "ambient".

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Using MTTF curve, it is seen that MTTF=80 years for 160°C junction temperature. In a design where higher MTTF is desired,

one option would be to run RF3806 at reduced VCC. Viewing UMTS ACP curves in graph section of data sheet, VCC=6V/25dBm

shows equivalent linearity to VCC=8V/26dBm. Reducing POUT specification to 25dBm will allow for higher MTTF while operat-

ing at VCC=6V. A practical approximation to Tj at adjusted operating condition can be made. Assume TCASE equal to 100.2°C,

as with VCC=8V and 26dBm out (conservative estimate). Dissipated power for 6V/25dBm/85°C is known from test data to

be 4.385W. From data sheet graph, RTH_JC=9.95°C/W. Tj is approximated to be:

Tj = 100.2 + 4.385 * 9.95 = 144°C

MTTF curve shows >450 years for this Tj. As mentioned, the above analysis is not exact, but does give us a practical way to get

an idea of where a condition will fall in terms of Tj and MTTF. Required data to do the calculation: data sheet curves and evalu-

ation board test in temperature chamber (to determine dissipated power).

Note that projected Tj vs Pout curves are included with DCS/PCS data (1800MHz-1990MHz high power application sche-

matic), to illustrate the same type of trade offs between operating at 6V and 8V. These curves are approximate, obtained with

the following method (called out in above paragraph):

1. UMTS evaluation board was converted to matching seen on DCS/PCS application schematic (changes @ input/out-

put/interstage/bias resistors at VREF).

2. Evaluation board was run in oven at 85°C ambient.

3. Dissipated power was calculated at each data point. Using RTH_JREF from data sheet curve, temperature delta to RF3806

junction (Tj) can be obtained. Tj was then plotted, and can be applied to MTTF vs Tj curve.

Finally, a description is included here for running two RF3806 in parallel with hybrid combiners. This approach enables design

to achieve substantial linearity enhancement for a given POUT, while maintaining low die temperature. In this example, hybrid

couplers (combiners) from Anaren (part number XC2100E-03) are used with 2 RF3806 UMTS evaluation boards. The bias con-

dition is VCC=6V, IREF=60mA. ACP performance vs temperature is shown in graph section, which can be compared to that for

single PA.

RFMD can be contacted to obtain RF3806 qualification report, which adheres to demanding infrastructure standards.

Rev A3 DS070509

7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical

support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.

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