7 Detailed Description

7.1 Overview

The OPA145 and OPA2145 (OPAx145) operational amplifiers are part of a family of low-power JFET input

amplifiers that feature superior drift performance and low input bias current. The rail-to-rail output swing and

input range that includes V– allow designers to use the low-noise characteristics of JFET amplifier while also

interfacing to modern, single-supply, precision, analog-to-digital converters (ADCs) and digital-to-analog

converters (DACs). The OPAx145 achieve 5.5-MHz gain-bandwidth product and 20-V/μs slew rate and consume

only 445 µA (typical) of quiescent current, making these devices an excellent choice for low-power applications.

These devices operate on a single 4.5-V to 36-V supply or dual ±2.25-V to ±18-V supplies.

The OPAx145 are fully specified from –40°C to +125°C for use in the most challenging environments. The

single-channel OPA145 is available in 5-pin SOT-23, 8-pin SOIC, and 8-pin VSSOP packages. The dual-channel

OPA2145 is available in 8-pin SOIC and 8-pin VSSOP packages.

Section 7.2 shows the simplified diagram of the OPAx145.

7.2 Functional Block Diagram

IN–

Pre-Output Driver

OUT

IN+

V+

V–

Copyright © 2017, Texas Instruments Incorporated

7.3 Feature Description

7.3.1 Capacitive Load and Stability

The dynamic characteristics of the OPAx145 have been optimized for commonly encountered gains, loads, and

operating conditions. The combination of low closed-loop gain and high capacitive loads decreases the phase

margin of the amplifier and can lead to gain peaking or oscillations. As a result, heavier capacitive loads must be

for example) in series with the output.

Figure 6-27 illustrates the effects on small-signal overshoot for several capacitive loads. Also, see Feedback

Plots Define Op Amp AC Performance, available for download from the TI website, for details of analysis

techniques and application circuits.

OPA145,, OPA2145

SBOS427E – JUNE 2017 – REVISED OCTOBER 2020

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