V

OUT

R = 20 kW

P

Op Amp V = GND

-

OPA333-Q1

V

IN

V+ = +5 V

-5 V

Additional

Negative

Supply

Copyright © 2017, Texas Instruments Incorporated

10

OPA333-Q1

SBOS522A – JUNE 2010 – REVISED NOVEMBER 2019

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8 Application and Implementation

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

The OPA333-Q1 is a unity-gain stable, precision operational amplifier with very low offset voltage drift. The

device is also free from output phase reversal. Applications with noisy or high-impedance power supplies require

decoupling capacitors close to the device power-supply pins. In most cases, 0.1-μF capacitors are adequate.

8.1.1 Achieving Output Swing to the Op Amp Negative Rail

Some applications require output voltage swings from 0 V to a positive full-scale voltage (such as 2.5 V) with

excellent accuracy. With most single-supply op amps, problems arise when the output signal approaches 0 V,

near the lower output swing limit of a single-supply op amp. A good single-supply op amp may swing close to

single-supply ground, but will not reach ground. The output of the OPA333-Q1 can be made to swing to ground,

or slightly below, on a single-supply power source. To do so requires the use of another resistor and an

additional, more negative, power supply than the op amp negative supply. A pulldown resistor may be connected

between the output and the additional negative supply to pull the output down below the value that the output

would otherwise achieve (see Figure 19).

Figure 19. VOUT Range to Ground

The OPA333-Q1 has an output stage that allows the output voltage to be pulled to its negative supply rail, or

slightly below, using the technique previously described. This technique only works with some types of output

stages. The OPA333-Q1 has been characterized to perform with this technique; however, the recommended

resistor value is approximately 20 k

Ω.

NOTE

This configuration increases the current consumption by several hundreds of microamps.

Accuracy is excellent down to 0 V and as low as –2 mV. Limiting and nonlinearity occur below –2 mV, but

excellent accuracy returns when the output is again driven above –2 mV. Lowering the resistance of the pulldown

resistor allows the op amp to swing even further below the negative rail. Resistors as low as 10 k

Ω can be used

to achieve excellent accuracy down to –10 mV.