THS4281 Datasheet, PDF (26/43 Pages) Texas Instruments – VERY LOW-POWER, HIGH-SPEED, RAIL-TO-RAIL INPUT AND OUTPUT VOLTAGE-FEEDBACK OPERATIONAL AMPLIFIER

THS4281
SLOS432B – APRIL 2004 – REVISED OCTOBER 2015
8 Application and Implementation
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NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
8.1.1 Single-Supply Operation
The THS4281 is designed to operate from a single 2.7-V to 16.5-V power supply. When operating from a single
power supply, care must be taken to ensure the input signal and amplifier are biased appropriately to allow for
the maximum output voltage swing and not violate V_ICR. The circuits shown in Figure 70 shows inverting and
noninverting amplifiers configured for single-supply operation.
+V_S
50-W Source
+
V_I
R_T 49.9 W _{_}
+V_S
2
R_g
2 kW
+V_S
2
V_O
R_f
2 kW
To Load
Power Supply Bypassing
Not Shown For Simplicity
R_f
50-W Source
R_g
V_I
51.1 W
2 kW
R_T
R_T
2 kW
V_S
_
+
+V_S
+V_S
2
2
C_T
V_O
To Load
Figure 70. DC-Coupled Single Supply Operation
8.1.2 Driving Capacitive Loads
One of the most demanding, and yet common, load conditions for an op amp is capacitive loading. Often, the
capacitive load is the input of an A/D converter, including additional external capacitance, which may be
recommended to improve A/D linearity. A high-speed, high open-loop gain amplifier like the THS4281 can be
susceptible to instability and peaking when a capacitive load is placed directly on the output. When the amplifier
open-loop output resistance is considered, this capacitive load introduces an additional pole in the feedback path
that decreases the phase margin. When the primary considerations are frequency response flatness, pulse
response fidelity, or distortion, a simple and effective solution is to isolate the capacitive load from the feedback
loop by inserting a small series isolation resistor (for example, R_(ISO) = 100 Ω for C_LOAD = 10 pF to R_(ISO) = 10 Ω
for C_LOAD = 1000 pF) between the amplifier output and the capacitive load.
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