Datasheet

THS452x
V
OUT-
V
OUT+
R
F
R
F
R
G
R
G
Single-Ended
Input
Differential
Output
V
S+
V
S-
THS452x
V
OUT-
V
IN-
V
OUT+
V
IN+
R
F
R
F
R
G
R
G
Differential
Input
Differential
Output
V
S+
V
S-
V
OUT+
´
R
R +R
G
G F
V
IN-
´
R
R +R
F
G F
+
THS4521
THS4522
THS4524
www.ti.com SBOS458F –DECEMBER 2008–REVISED SEPTEMBER 2011
APPLICATION INFORMATION
The following circuits show application information for
the THS4521, THS4522, and THS4524 family. For
simplicity, power-supply decoupling capacitors are
not shown in these diagrams; see the EVM and
Layout Recommendations section for suggested
guidelines. For more details on the use and operation
of fully differential op amps, refer to the Application
Report Fully-Differential Amplifiers (SLOA054),
available for download from the TI web site at
www.ti.com.
Differential Input to Differential Output
Amplifier
The THS4521, THS4522, and THS4524 family are
fully-differential operational amplifiers that can be
Figure 61. Single-Ended Input to Differential
used to amplify differential input signals to differential
Output Amplifier
output signals. Figure 60 shows a basic block
diagram of the circuit (V
OCM
and PD inputs not
shown). The gain of the circuit is set by R
F
divided by
Input Common-Mode Voltage Range
R
G
.
The input common-mode voltage of a fully-differential
op amp is the voltage at the + and – input pins of the
device.
It is important to not violate the input common-mode
voltage range (V
ICR
) of the op amp. Assuming the op
amp is in linear operation, the voltage across the
input pins is only a few millivolts at most. Therefore,
finding the voltage at one input pin determines the
input common-mode voltage of the op amp.
Treating the negative input as a summing node, the
voltage is given by Equation 1:
(1)
Figure 60. Differential Input to Differential Output
To determine the V
ICR
of the op amp, the voltage at
Amplifier
the negative input is evaluated at the extremes of
V
OUT+
. As the gain of the op amp increases, the input
Single-Ended Input to Differential Output
common-mode voltage becomes closer and closer to
Amplifier
the input common-mode voltage of the source.
The THS4521, THS4522, and THS4524 family can
also amplify and convert single-ended input signals to
Setting the Output Common-Mode Voltage
differential output signals. Figure 61 illustrates a basic
The output common-model voltage is set by the
block diagram of the circuit (V
OCM
and PD inputs not
voltage at the V
OCM
pin. The internal common-mode
shown). The gain of the circuit is again set by R
F
control circuit maintains the output common-mode
divided by R
G
.
voltage within 5-mV offset (typ) from the set voltage.
If left unconnected, the common-mode set point is set
to midsupply by internal circuitry, which may be
overdriven from an external source.
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Product Folder Link(s): THS4521 THS4522 THS4524