OP275
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
THD + NOISE – %
APPLICATIONS
Circuit Protection
0.010
V
S
=
18V
R
L
= 600
0.001
0.0001
0.5
1
OUTPUT SWING – V rms
10
Figure 4. Headroom, THD + Noise vs. Output
Amplitude (V rms); R
LOAD
= 600
, V
SUP
= ±18 V
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
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
–
A1
+
R
X
332
FEEDBACK
V
OUT
0.001
R
L
= 600
V
OUT
= 10V rms @ 1kHz
0.01
A1 = 1/2 OP275
Figure 1. Recommended Output Short-Circuit Protection
0.010
THD + NOISE – %
R
L
= 600
, 2k
, 10k
V
S
=
15V
V
IN
= 3V rms
A
V
= +1
THD – %
0.1
0
17
0.001
18
19
20
SUPPLY VOLTAGE – V
21
22
0.0005
Figure 5. THD + Noise vs. Supply Voltage
20
100
FREQUENCY – Hz
1k
10k
20k
Noise
Figure 2. THD + Noise vs. Frequency vs. R
LOAD
1
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
MKR: 45.6
V/
Hz
10.0
V/DIV
THD + NOISE – %
0.1
600
0.010
A
V
= +1
V
S
=
18V
V
IN
= 10V rms
80kHz FILTER
2k
0.001
10k
0.0001
20
100
FREQUENCY – Hz
1k
10k
20k
Figure 3. THD + Noise vs. R
LOAD
; V
IN
=10 V rms
0Hz
MKR:
2.24Hz
10Hz
BW: 0.145Hz
Figure 6. 1/f Noise Corner, V
S
= ±15 V, A
V
= 1000
REV. C
–7–
AD [ ANALOG DEVICES ]
