THS6182_08 Datasheet, PDF (22/35 Pages) Texas Instruments – LOW-POWER DISSIPATION ADSL LINE DRIVER

THS6182
SLLS544H – SEPTEMBER 2002 – REVISED JUNE 2007
APPLICATION INFORMATION (continued)
ǒ Ǔ PD +
TMAX–TA
q_JA
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Where:
P_D = Maximum power dissipation of THS6182 (watts)
T_MAX = Absolute maximum operating junction temperature (125°C)
T_A = Free-ambient air temperature (°C)
θ_JA = θ_JC + θ_CA
θ_JC = Thermal coefficient from junction to case. See the Package Dissipation Ratings table.
θ_CA = Thermal coefficient from case to ambient determined by PCB layout and construction.
More complete details of the PowerPAD installation process and thermal management techniques can be found
in the Texas Instruments Technical Brief, PowerPAD Thermally Enhanced Package. This document can be
found at the TI web site (www.ti.com) by searching on the key word PowerPAD. The document can also be
ordered through your local TI sales office. Refer to literature number SLMA002 when ordering.
GENERAL CONFIGURATIONS
A common error for the first-time CFB user is to create a unity gain buffer amplifier by shorting the output directly
to the inverting input. A CFB amplifier in this configuration oscillates and is not recommended. The THS6182,
like all CFB amplifiers, must have a feedback resistor for stable operation. Additionally, placing capacitors
directly from the output to the inverting input is not recommended. This is because, at high frequencies, a
capacitor has a very low impedance. This results in an unstable amplifier and should not be considered when
using a current-feedback amplifier. Because of this, integrators and simple low-pass filters, which are easily
implemented on a VFB amplifier, have to be designed slightly differently. If filtering is required, simply place an
RC-filter at the noninverting terminal of the operational-amplifier (see Figure 75).
R_G
R_F
V_I
R1
−
+
C1
V_O
ǒ Ǔǒ Ǔ ^VO
VI
+
1
)
RF
RG
1
1 ) sR1C1
f–3dB
+
1
2pR1C1
Figure 75. Single-Pole Low-Pass Filter
If a multiple pole filter is required, the use of a Sallen-Key filter can work very well with CFB amplifiers. This is
because the filtering elements are not in the negative feedback loop and stability is not compromised. Because
of their high slew-rates and high bandwidths, CFB amplifiers can create very accurate signals and help minimize
distortion. An example is shown in Figure 76.
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