Texas Instruments THS3115 EVM, Руководство пользователя

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Noninverting Stage (Channel 2) Operation
3-4
3.2 Noninverting Stage (Channel 2) Operation
Noninverting stage operation was shown in Chapter 2 of this manual. The
default configuration is a 50-
W
terminated input (R8), a 50-
W
matching resistor
output (R11B), and a 100-
W
load (R12B). The terminating and matching values
can be changed if the user requires different termination and matching—for
example, 75-
W
video applications. The load resistor, however, should not be
changed because many op amp specifications are measured at this load. Gain
of the stage can be modified by changing the values of R9 and R10.
Figure 3--2. Noninverting Gain Stage
J9
OUT2
R12B
100
W
J7
+IN2
R8
49.9
W
R10
909
W
R9
909
W
R7
0
R11B
49.9
W
--
+
U1B
THS31x5PWP
12
11
13
The gain of the circuit as populated is 2 with a high impedance load, and 1 with
a 50-
W
load. This circuit does not exhibit the reduction in input voltage level
described for the inverting stage—as the input is connected directly to a high
impedance input of the op amp.
The circuit of Figure 3--2 can be utilized as a video driver if the 49.9-
W
resistors
are removed and 75-
W
resistors are substituted.
3.3 Shut Down Operation (Channels 1 and 2)
The output of channels 1 and 2 can both be shut down simultaneously when
a voltage above 2 VDC is applied to the shut down input (TP2 on the EVM).
In shut down mode, the output goes to ground. Normal operation is restored
for voltages below 0.8 V on the shut down input.