OPA2673 Datasheet, PDF (25/40 Pages) Texas Instruments – Dual, Wideband, High Output Current Operational Amplifier with Active Off-Line Control

OPA2673
www.ti.com..................................................................................................................................................... SBOS382A – JUNE 2008 – REVISED OCTOBER 2008
TOTAL DRIVER POWER FOR LINE DRIVER
APPLICATIONS
The total internal power dissipation for the OPA2673
in a line driver application is the sum of the quiescent
power and the output stage power. The OPA2673
holds a relatively constant quiescent current versus
supply voltage—giving a power contribution that is
simply the quiescent current times the supply voltage
used (the supply voltage is greater than the solution
given in Equation 9). The total output stage power
may be computed with reference to Figure 81.
+V_CC
I_AVG
=
I_P
C_F
DESIGN-IN TOOLS
Demonstration Fixtures
Two printed circuit boards (PCBs) are available to
assist in the initial evaluation of circuit performance
using the OPA2673 in its two package options. Both
of these are offered free of charge as unpopulated
PCBs, delivered with a user’s guide. The summary
information for these fixtures is shown in Table 2.
Table 2. Demonstration Fixtures by Package
PRODUCT
OPA2673IRGV
OPA2673IDGQ
PACKAGE
QFN-16
MSOP-10
ORDERING
NUMBER
DEM-OPA-QFN-2A
DEM-OPA-MSOP-2A
LITERATURE
NUMBER
SBOU067
SBOU068
These demonstration fixtures can be requested
R_T
through the Texas Instruments web site (www.ti.com).
Figure 81. Output Stage Power Model
The two output stages used to drive the load of
Figure 79 can be seen as an H-Bridge in Figure 81.
The average current drawn from the supply into this
H-Bridge and load is the peak current in the load
given by Equation 6 divided by the crest factor (CF).
This total power from the supply is then reduced by
the power in R_T to leave the power dissipated internal
to the drivers in the four output stage transistors. That
power is simply the target line power used in
Equation 7 plus the power lost in the matching
elements (R_M). In the examples here, a perfect match
is targeted giving the same power in the matching
elements as in the load. The output stage power is
then set by Equation 10.
P_OUT =
I_P
C_F
´ V_CC - 2P_L
(10)
The total amplifier power is then:
P_TOT = I_Q ´ V_CC +
I_P
C_F
´ V_CC - 2P_L
(11)
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Macromodels and Applications Support
Computer simulation of circuit performance using
SPICE is often useful when analyzing the
performance of analog circuits and systems. This
technique is particularly true for video and RF
amplifier circuits where parasitic capacitance and
inductance can have a major effect on circuit
performance. A SPICE model for the OPA2673 is
available through the TI web site (www.ti.com). This
model does a good job of predicting small-signal ac
and transient performance under a wide variety of
operating conditions, but does not do as well in
predicting the harmonic distortion or dG/dΦ
characteristics. This model does not attempt to
distinguish between the package types in small-signal
ac performance, nor does it attempt to simulate
channel-to-channel coupling.
OPERATING SUGGESTIONS
Setting Resistor Values to Optimize Bandwidth
A current-feedback op amp such as the OPA2673
can hold an almost constant bandwidth over signal
gain settings with the proper adjustment of the
external resistor values, which are shown in the
Typical Characteristics; the small-signal bandwidth
decreases only slightly with increasing gain. These
characteristic curves also show that the feedback
resistor is changed for each gain setting. The resistor
values on the inverting side of the circuit for a
current-feedback op amp can be treated as frequency
response compensation elements, whereas the ratios
set the signal gain.
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): OPA2673
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