8.3.1 Operating Suggestions

8.3.1.1 Setting Resistor Values to Optimize Bandwidth

A current-feedback op amp such as the OPA2675 can hold an almost constant bandwidth over signal

gain settings with the proper adjustment of the external resistor values, which are shown in the Typical

Characteristics; the small-signal bandwidth decreases only slightly with increasing gain. These characteristic

inverting side of the circuit for a current-feedback op-amp can be treated as a frequency response compensation

Figure 8-2 shows the small-signal frequency response analysis circuit for the OPA2675.

V

O

R

G

V

I

R

I

Z

I

a

R

F

I

ERR

Figure 8-2. Current-Feedback Transfer Function

Analysis Circuit

600

500

400

300

200

NoiseGain

0

20

10

15

5

Figure 8-3. Feedback Resistor Versus Noise Gain

The key elements of this current-feedback op amp model are:

α = buffer gain from the noninverting input to the inverting input

NG=NoiseGain=1+

R

G

R

F

(1)

A current-feedback op amp senses an error current in the inverting node (as opposed to a differential input

error voltage for a voltage-feedback op amp) and passes this on to the output through an internal frequency-

dependent transimpedance gain. The Typical Characteristics show this open-loop transimpedance response,

which is analogous to the open-loop voltage gain curve for a voltage-feedback op amp. Refer to the training

videos shown in TI Precision Labs for further understanding on the CFA operating theory.

Typical Characteristics and give a good starting point for designs where bandwidth optimization is desired.

8.3.1.2 Output Current and Voltage

The OPA2675 provides output voltage and current capabilities that are unsurpassed in a low-cost dual

monolithic op amp. Under no-load conditions at +25°C, the output voltage typically swings closer than 1.1 V

to either supply rail; the tested (+25°C) swing limit is within 1.2 V of either rail. The OPA2675 is capable of

delivering around 1000 mA of source and sink current at room temperature. Figure 8-4 and Figure 8-5 shows the

relation between current output of the OPA2675 at different temperatures and maximum voltage swing at that

current output under loaded conditions.

OPA2675

SBOSAA5B – APRIL 2022 – REVISED SEPTEMBER 2022

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