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 compensa-
tion network.
Figures 3c and 3d show compensation techniques for
noninverting amplifiers. Like the follower circuits, the cir-
cuit 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 600Ω load with power
supply voltages up to
±24V.
Internal power dissipation is
increased when operating at high power supply voltage. The
typical performance 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 device
directly to the circuit board and use wide circuit board
traces.
OUTPUT CURRENT LIMIT
Output current is limited by internal circuitry to approxi-
mately
±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
1
R
3
OPA604
V
O
= 10Vp-p
(3.5Vrms)
10
100
101
101
101
R
1
∞
500Ω
50Ω
R
2
5kΩ
5kΩ
5kΩ
R
3
50Ω
500Ω
∞
Generator
Output
Analyzer
Input
Audio Precision
System One
Analyzer
(1)
R
L
1kΩ
IBM PC
or
Compatible
NOTE: (1) Measurement BW = 80kHz
FIGURE 2. Distortion Test Circuit.
®
OPA604
8
BURR-BROWN [ BURR-BROWN CORPORATION ]
