For the unity-gain buffer, Figure 3a, stability is preserved by
adding a phase-lead network, R
C
and C
C
. Voltage drop
across R
C
will reduce output voltage swing with heavy loads.
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.
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 600Ω 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.
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
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.
R
1
R
2
SIG. DIST.
GAIN GAIN
R
1
∞
R
2
R
3
1
R
3
OPA604
101
101
101
5k
Ω
5k
Ω
5k
Ω
50
Ω
500
Ω
∞
V
O
= 10Vp-p
(3.5Vrms)
10
100
500
Ω
50
Ω
Generator
Output
Analyzer
Input
Audio Precision
System One
Analyzer
(1)
R
L
1k
Ω
IBM PC
or
Compatible
NOTE: (1) Measurement BW = 80kHz
FIGURE 2. Distortion Test Circuit.
8
OPA604
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SBOS019A
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