Applications Hint

Amplifier Topolgy

The topology chosen for the LMC6034, shown in

Figure 1,is

unconventional (compared to general-purpose op amps) in

that the traditional unity-gain buffer output stage is not used;

instead, the output is taken directly from the output of the in-

tegrator, to allow a larger output swing. Since the buffer tra-

ditionally delivers the power to the load, while maintaining

high op amp gain and stability, and must withstand shorts to

either rail, these tasks now fall to the integrator.

As a result of these demands, the integrator is a compound

affair with an embedded gain stage that is doubly fed forward

(via C

driver. In addition, the output portion of the integrator is a

push-pull configuration for delivering heavy loads. While

sinking current the whole amplifier path consists of three

gain stages with one stage fed forward, whereas while

sourcing the path contains four gain stages with two fed

forward.

Output Characteristics

Current Sourcing

DS011134-27

Input Voltage Noise

vs Frequency

DS011134-28

CMRR vs Frequency

DS011134-29

Open-Loop Frequency

Response

DS011134-30

Frequency Response

vs Capacitive Load

DS011134-31

Non-Inverting Large Signal

Pulse Response

DS011134-32

Stability vs

Capacitive Load

DS011134-33

Stability vs

Capacitive Load

DS011134-34

Note: Avoid resistive loads of less than 500

Ω, as they may cause instability.

www.national.com

5