Datasheet

R
T
+V
CC
I =
AVG
I
P
C
F
P =
OUT
C
F
I
P
´ -
CC
V 2P
L
P =I V +
TOT
Q
´
CC
C
F
I
P
´ -
CC
V 2P
L
OPA2673
www.ti.com SBOS382F –JUNE 2008–REVISED MAY 2010
TOTAL DRIVER POWER FOR LINE DRIVER DESIGN-IN TOOLS
APPLICATIONS
Demonstration Fixture
The total internal power dissipation for the OPA2673
in a line driver application is the sum of the quiescent A printed circuit board (PCB) is available to assist in
power and the output stage power. The OPA2673 the initial evaluation of circuit performance using the
holds a relatively constant quiescent current versus OPA2673 in its QFN package option. This demo
supply voltage—giving a power contribution that is board is offered free of charge as an unpopulated
simply the quiescent current times the supply voltage PCB, delivered with a user’s guide. The summary
used (the supply voltage is greater than the solution information for this fixture is shown in Table 2.
given in Equation 9). The total output stage power
may be computed with reference to Figure 81. Table 2. Demonstration Fixture by Package
ORDERING LITERATURE
PRODUCT PACKAGE NUMBER NUMBER
OPA2673IRGV QFN-16 DEM-OPA-QFN-2A SBOU067
This demonstration fixture can be requested through
the Texas Instruments web site (www.ti.com).
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
Figure 81. Output Stage Power Model
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
The two output stages used to drive the load of
and transient performance under a wide variety of
Figure 79 can be seen as an H-Bridge in Figure 81.
operating conditions, but does not do as well in
The average current drawn from the supply into this
predicting the harmonic distortion or dG/dΦ
H-Bridge and load is the peak current in the load
characteristics. This model does not attempt to
given by Equation 6 divided by the crest factor (CF).
distinguish between the package types in small-signal
This total power from the supply is then reduced by
ac performance, nor does it attempt to simulate
the power in R
T
to leave the power dissipated internal
channel-to-channel coupling.
to the drivers in the four output stage transistors. That
power is simply the target line power used in
OPERATING SUGGESTIONS
Equation 7 plus the power lost in the matching
elements (R
M
). In the examples here, a perfect match
Setting Resistor Values to Optimize Bandwidth
is targeted giving the same power in the matching
elements as in the load. The output stage power is
A current-feedback op amp such as the OPA2673
then set by Equation 10.
can hold an almost constant bandwidth over signal
gain settings with the proper adjustment of the
external resistor values, which are shown in the
(10)
Typical Characteristics; the small-signal bandwidth
decreases only slightly with increasing gain. These
The total amplifier power is then:
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
(11)
current-feedback op amp can be treated as frequency
space
response compensation elements, whereas the ratios
set the signal gain.
space
space
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