OP275_ データシートの表示（PDF） - Analog Devices

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OP275_

Low-Noise / Precision Operational Amplifier

Analog Devices 

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 ISC +

= 40 mA and ISC– = –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. VIN (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

VS = ±18V

RL = 600Ω

0.0001

0.5

1

10

OUTPUT SWING – V rms

Figure 4. Headroom, THD + Noise vs. Output Amplitude

(V rms); RLOAD = 600 Ω, VSUP = ±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

VOUT

A1 = 1/2 OP275

Figure 1. Recommended Output Short Circuit Protection

0.010

RL = 600Ω, 2k, 10k

VS = ±15V

VIN = 3V rms

AV = +1

0.0001

0.001

0.01

0.1

RL = 600Ω

VOUT = 10 Vrms @ 1kHz

0.001

0.0005

20

100

1k

FREQUENCY – Hz

10k 20k

Figure 2. THD + Noise vs. Frequency vs. RLOAD

1

0.1

0.010

0.001

600Ω

AV = +1

VS = ±18V

VIN = 10V rms

80kHz FILTER

2k

0.0001

20

10k

100

1k

FREQUENCY – Hz

10k 20k

Figure 3. THD + Noise vs. RLOAD; VIN =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, VS = ±15 V, AV = 1000

REV. A

–7–

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