OPA604

8

SBOS019A

www.ti.com

For the unity-gain buffer, Figure 3a, stability is preserved by

An alternate circuit, Figure 3b, does not limit the output with

low load impedance. It provides a small amount of positive

feedback to reduce the net feedback factor. Input impedance

of this circuit falls at high frequency as op amp gain rolloff

reduces the bootstrap action on the compensation network.

Figures 3c and 3d show compensation techniques for

noninverting amplifiers. Like the follower circuits, the circuit in

Figure 3d eliminates voltage drop due to load current, but at

the penalty of somewhat reduced input impedance at high

frequency.

Figures 3e and 3f show input lead compensation networks

for inverting and difference amplifier configurations.

NOISE PERFORMANCE

Op amp noise is described by two parameters—noise volt-

age and noise current. The voltage noise determines the

noise performance with low source impedance. Low noise

bipolar-input op amps such as the OPA27 and OPA37

provide very low voltage noise. But if source impedance is

greater than a few thousand ohms, the current noise of

bipolar-input op amps react with the source impedance and

will dominate. At a few thousand ohms source impedance

and above, the OPA604 will generally provide lower noise.

POWER DISSIPATION

The OPA604 is capable of driving a 600

Ω load with power-

supply voltages up to

±24V. Internal power dissipation is

increased when operating at high power supply voltage. The

typical characteristic curve, Power Dissipation vs Power

Supply Voltage, shows quiescent dissipation (no signal or no

load) as well as dissipation with a worst case continuous sine

wave. Continuous high-level music signals typically produce

dissipation significantly less than worst-case sine waves.

Copper leadframe construction used in the OPA604 im-

proves heat dissipation compared to conventional plastic

packages. To achieve best heat dissipation, solder the de-

vice directly to the circuit board and use wide circuit board

traces.

OUTPUT CURRENT LIMIT

Output current is limited by internal circuitry to approximately

±40mA at 25°C. The limit current decreases with increasing

temperature as shown in the typical curves.

FIGURE 2. Distortion Test Circuit.

R

2

OPA604

R

1

R

3

V

(3.5Vrms)

Generator

Output

Analyzer

Input

Audio Precision

System One

R

L

1k

Ω

IBM PC

or

Compatible

SIG.

GAIN

DIST.

GAIN

R

1

R

2

R

3

∞

500

Ω

50

Ω

5k

Ω

5k

Ω

5k

Ω

50

Ω

500

Ω

∞

1

10

100

101

101

101

NOTE: (1) Measurement BW = 80kHz