V

OUT

500µA

OPA365

V

IN

V+=+5V

Op Amp

Negative

Supply

Grounded

−V = −5V

(Additional

Negative Supply)

OPA365-EP

SLOS735

– AUGUST 2011

www.ti.com

Achieving an Output Level of Zero Volts (0V)

Certain single-supply applications require the op amp output to swing from 0 V to a positive full-scale voltage and

have high accuracy. An example is an op amp employed to drive a single-supply ADC having an input range

from 0 V to 5 V. Rail-to-rail output amplifiers with very light output loading may achieve an output level within

as the load current required increases. This increased deviation is a result of limitations of the CMOS output

stage.

When a pulldown resistor is connected from the amplifier output to a negative voltage source, the OPA365 can

achieve an output level of 0 V, and even a few millivolts below 0 V. Below this limit, nonlinearity and limiting

conditions become evident. Figure 8 illustrates a circuit using this technique.

Figure 8. Swing-to-Ground

A pulldown current of approximately 500

µA is required when OPA365 is connected as a unity-gain buffer. A

resistors that load the output during positive output voltage excursions.

Note that this technique does not work with all op amps and should only be applied to op amps such as the

OPA365 that have been specifically designed to operate in this manner. Also, operating the OPA365 output at

0 V changes the output stage operating conditions, resulting in somewhat lower open-loop gain and bandwidth.

Keep these precautions in mind when driving a capacitive load because these conditions can affect circuit

transient response and stability.

12

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