OP275_15 Datasheet, PDF (7/12 Pages) Analog Devices – Dual Bipolar/JFET, Audio Operational Amplifier

OP275
APPLICATIONS
Circuit Protection
OP275 has been designed with inherent short-circuit protection
to ground. An internal 30  resistor, in series with the output,
limits the output current at room temperature to I_SC+ = 40 mA
and I_SC– = –90 mA, typically, with ±15 V supplies.
However, shorts to either supply may destroy the device when
excessive voltages or currents are applied. If it is possible for a
user to short an output to a supply for safe operation, the output
current of the OP275 should be design-limited to ±30 mA, as
shown in Figure 1.
Total Harmonic Distortion
Total Harmonic Distortion + Noise (THD + N) of the OP275 is
well below 0.001% with any load down to 600 . However, this is
dependent upon the peak output swing. In Figure 2, the THD +
Noise with 3 V rms output is below 0.001%. In Figure 3, THD +
Noise is below 0.001% for the 10 k and 2 k loads but increases
to above 0.1% for the 600  load condition. This is a result of the
output swing capability of the OP275. Notice the results in Figure 4,
showing THD versus V_IN (V rms). This figure shows that the THD
+ Noise remains very low until the output reaches 9.5 V rms. This
performance is similar to competitive products.
R_FB
FEEDBACK
–
R_X
332 
A1
V_OUT
+
A1 = 1/2 OP275
Figure 1. Recommended Output Short-Circuit Protection
0.010
R_L = 600, 2k, 10k
V_S = 15V
V_IN = 3V rms
A_V = +1
0.001
0.0005
20
100
1k
FREQUENCY – Hz
10k 20k
Figure 2. THD + Noise vs. Frequency vs. R_LOAD
1
0.1
0.010
0.001
600
A_V = +1
V_S = 18V
V_IN = 10V rms
80kHz FILTER
2k
0.0001
20
10k
100
1k
FREQUENCY – Hz
10k 20k
Figure 3. THD + Noise vs. R_LOAD; V_IN =10 V rms
0.010
0.001
V_S = 18V
R_L = 600
0.0001
0.5
1
10
OUTPUT SWING – V rms
Figure 4. Headroom, THD + Noise vs. Output
Amplitude (V rms); R_LOAD = 600  , V_SUP = ±18 V
The output of the OP275 is designed to maintain low harmonic
distortion while driving 600  loads. However, driving 600 
loads with very high output swings results in higher distortion if
clipping occurs. A common example of this is in attempting to
drive 10 V rms into any load with ±15 V supplies. Clipping will
occur and distortion will be very high. To attain low harmonic
distortion with large output swings, supply voltages may be
increased. Figure 5 shows the performance of the OP275 driving
600  loads with supply voltages varying from ±18 V to ±20 V.
Notice that with ±18 V supplies the distortion is fairly high, while
with ±20 V supplies it is a very low 0.0007%.
0.0001
0.001
0.01
RL = 600
V_OUT = 10V rms @ 1kHz
0.1
0
17
18
19
20
21
22
SUPPLY VOLTAGE – V
Figure 5. THD + Noise vs. Supply Voltage
Noise
The voltage noise density of the OP275 is below 7 nV/^Hz from
30 Hz. This enables low noise designs to have good performance
throughout the full audio range. Figure 6 shows a typical OP275
with a 1/f corner at 2.24 Hz.
CH A: 80.0V FS
10.0V/DIV
MKR: 45.6V/ Hz
0Hz
MKR: 2.24Hz
10Hz
BW: 0.145Hz
Figure 6. 1/f Noise Corner, V_S = ±15 V, A_V = 1000
REV. C
–7–