THS3202_16 Datasheet, PDF (23/37 Pages) Texas Instruments – 2-GHz, LOW DISTORTION, DUAL CURRENT-FEEDBACK AMPLIFIERS

THS3202
www.ti.com
SLOS242F – SEPTEMBER 2002 – REVISED JANUARY 2010
For systems where heat dissipation is more critical, the THS320x family of devices is offered in an MSOP-8 with
PowerPAD. 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
T_J = 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
T_A − 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 81. 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 82. 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.
R_g
R_f
Input
_
THS3202
+
10 Ω
Output
C_LOAD
Figure 82. Driving a Capacitive Load
Copyright © 2002–2010, Texas Instruments Incorporated
Product Folder Link(s): THS3202
Submit Documentation Feedback
23