OPA3690ID Datasheet, PDF (17/39 Pages) Texas Instruments – Triple, Wideband, Voltage-Feedback OPERATIONAL AMPLIFIER with Disable

OPA3690
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BUFFERED 2 x 1 MULTIPLEXER
Using two of the three channels in an OPA3690 to
select one of two possible input signals, then using
the 3rd to isolate the summing point and drive the
load, will give a very flexible, wideband, multiplexing
capability. See Figure 44 for one example of this
where the two input stages have been set up for a
gain of +2.
Summing the two output signals together at the
output stage buffer noninverting input through 400Ω
resistors allows excellent isolation between the two
channels to be maintained. When one channel is
operating, the other will see an attenuated version of
the active channel signal on its inverting node. In this
circuit, that signal is attenuated by 20dB at this
inactive inverting input—this will keep the swing low
enough on the off channel to avoid parasitic turn-on
at that input stage. The desired signal is attenuated
by 0.6V/V due to this resistor divider, then recovered
by the gain set in the output stage.
One modification to this circuit would give a
high-speed switched gain. The same signal would be
fed into both inputs and each amplifier would be set
to a different gain.
TRIPLE ADC DRIVER
Figure 43 shows the OPA3690 driving a triple ADC.
Most ADCs are defined for single +5V operation. The
SBOS237G – MARCH 2002 – REVISED MARCH 2010
OPA3690 can be adapted to single +5V as well,
using the techniques described for Figure 37. The
signal flowthrough pinout for the OPA3690 allows a
higher signal fidelity through higher frequencies due
to the simplified PCB layout requirements.
200W
V₁
402W
1/3
OPA3690
402W
24.9W
100pF
200W
V₂
402W
1/3
OPA3690
402W
24.9W
100pF
Triple
ADC
200W
V₃
402W
1/3
OPA3690
402W
24.9W
100pF
Figure 43. Triple ADC Driver
+5V
V_DIS
2kW
+5V
Video 1
75W
49.9W
1/3 ^DIS
OPA3690
402W
100W
100W
Video 2
75W
49.9W
2kW
-5V
100W
100W
+5V
1/3
OPA3690
DIS
-5V
402W
+5V
1/3
OPA3690
DIS
75W
-5V
249W
374W
Figure 44. Buffered 2 x 1 Multiplexer
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Product Folder Link(s): OPA3690
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