OP275 Datasheet, PDF (7/12 Pages) Analog Devices – Dual Bipolar/JFET, Audio Operational Amplifier

OP275
APPLICATIONS
Short Circuit Protection
The OP275 has been designed with inherent short circuit pro-
tection to ground. An internal 30 Ω 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 out-
put 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 Ω. However,
this is dependent upon the peak output swing. In Figure 2 it is
seen that the THD + Noise with 3 V rms output is below
0.001%. In the following Figure 3, THD + Noise is below
0.001% for the 10 kΩ and 2 kΩ loads but increases to above
0.1% for the 600␣ Ω load condition. This is a result of the output
swing capability of the OP275. Notice the results in Figure 4,
showing THD vs. V_IN (V rms). This figure shows that the THD
+ Noise remains very low until the output reaches 9.5 volts rms.
This performance is similar to competitive products.
RFB
0.010
0.001
V_S = ±18V
R_L = 600Ω
0.0001
0.5
1
10
OUTPUT SWING – V rms
Figure 4. Headroom, THD + Noise vs. Output Amplitude
(V rms); R_LOAD = 600 Ω, V_SUP = ±18 V
The output of the OP275 is designed to maintain low harmonic
distortion while driving 600 Ω loads. However, driving 600 Ω
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 volt 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 perfor-
mance of the OP275 driving 600␣ Ω loads with supply voltages
varying from ± 18 volts to ± 20 volts. Notice that with ± 18 volt
supplies the distortion is fairly high, while with ± 20 volt supplies
it is a very low 0.0007%.
FEEDBACK
RX
332Ω
A1
V_OUT
A1 = 1/2 OP275
Figure 1. Recommended Output Short Circuit Protection
0.010
R_L = 600Ω, 2k, 10k
V_S = ±15V
V_IN = 3V rms
A_V = +1
0.0001
0.001
0.01
0.1
RL = 600Ω
V_OUT = 10 Vrms @ 1kHz
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
600Ω
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,
±18 V Supplies
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 perfor-
mance throughout the full audio range. Figure 6 shows a typical
OP275 with a 1/f corner at 2.24 Hz.
CH A: 80.0 µV FS
10.0 µV/DIV
MKR: 45.6 µV/√Hz
0 Hz
MKR: 2.24 Hz
10 Hz
BW: 0.145 Hz
Figure 6. 1/f Noise Corner, V_S = ±15 V, A_V = 1000
REV. A
–7–