THS3202 Datasheet, PDF (24/32 Pages) Texas Instruments – 2-GHZ, LOW DISTORTION, CURRENT FEEDBACK AMPLIFIERS

THS3202
SLOS242D − SEPTEMBER 2002 − REVISED JANUARY 2004
www.ti.com
For systems where heat dissipation is more critical, the THS320x family of devices is offered in an 8-pin MSOP with
PowerPAD and the THS3202 is available in the SOIC−8 PowerPAD package offering even better thermal
performance. The thermal coefficient for the PowerPAD packages are substantially improved over the traditional
SOIC. Maximum power dissipation levels are depicted in the graph for the available packages. The data for the
PowerPAD packages assume a board layout that follows the PowerPAD layout guidelines referenced above and
detailed in the PowerPAD application note number SLMA002. The following graph also illustrates the effect of not
soldering the PowerPAD to a PCB. The thermal impedance increases substantially which may cause serious heat
and performance issues. Be sure to always solder the PowerPAD to the PCB for optimum performance.
4.0
TJ = 125°C
3.5
3.0
θ_JA = 58.4°C/W
2.5
θ_JA = 98°C/W
2.0
1.5
1.0
0.5
θ_JA = 158°C/W
0.0
−40 −20 0 20 40 60 80 100
TA − Free-Air Temperature − °C
Results are With No Air Flow and PCB Size = 3”x3”
θ_JA = 58.4°C/W for 8-Pin MSOP w/PowerPad (DGN)
θ_JA = 98°C/W for 8-Pin SOIC High Test PCB (D)
θ_JA = 158°C/W for 8-Pin MSOP w/PowerPad w/o Solder
Figure 94. Maximum Power Dissipation vs Ambient Temperature
When determining whether or not the device satisfies the maximum power dissipation requirement, it is important
to not only consider quiescent power dissipation, but also dynamic power dissipation. Often times, this is difficult to
quantify because the signal pattern is inconsistent, but an estimate of the RMS power dissipation can provide visibility
into a possible problem.
DRIVING A CAPACITIVE LOAD
Driving capacitive loads with high-performance amplifiers is not a problem as long as certain precautions are taken.
The first is to realize that the THS3202 has been internally compensated to maximize its bandwidth and slew-rate
performance. When the amplifier is compensated in this manner, capacitive loading directly on the output decreases
the device’s phase margin leading to high-frequency ringing or oscillations. Therefore, for capacitive loads of greater
than 10 pF, it is recommended that a resistor be placed in series with the output of the amplifier, as shown in Figure 95.
A minimum value of 10 Ω should work well for most applications. For example, in 75-Ω transmission systems, setting
the series resistor value to 75 Ω both isolates any capacitance loading and provides the proper line impedance
matching at the source end.
Rg
Rf
Input
_
THS3202
+
10 Ω
Output
CLOAD
Figure 95. Driving a Capacitive Load
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