OP162GS datasheet(16/20 Pages) AD

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OP162/OP262/OP462

Rev. F | Page 16 of 20

APPLICATION CIRCUITS

SINGLE-SUPPLY STEREO HEADPHONE DRIVER

Figure 46 shows a stereo headphone output amplifier that can

operate from a single 5 V supply. The reference voltage is

derived by dividing the supply voltage down with two 100 kΩ

resistors. A 10 µF capacitor prevents power supply noise from

contaminating the audio signal and establishes an ac ground for

the volume control potentiometers.

The audio signal is ac-coupled to each noninverting input

through a 10 µF capacitor. The gain of the amplifier is con-

trolled by the feedback resistors and is (R2/R1) + 1. For this

example, the gain is 6. By removing R1, the amplifier would

have unity gain. To short-circuit protect the output of the

device, a 169 Ω resistor is placed at the output in the feedback

network. This prevents any damage to the device if the head-

phone output becomes shorted. A 270 µF capacitor is used at

the output to couple the amplifier to the headphone. This value

is much larger than that used for the input because of the low

impedance of headphones, which can range from 32 Ω to 600 Ω

or more.

OP262-A

169

Ω

270

µF

47k

Ω

L VOLUME

CONTROL

R1 = 10k

Ω

µF

10k

Ω

100k

Ω

µF

100k

Ω

R2 = 50k

Ω

LEFT IN

OP262-B

169

Ω

270

µF

47k

Ω

HEADPHONE

RIGHT

HEADPHONE

LEFT

10k

Ω

R VOLUME

CONTROL

µF

RIGHT IN

R2 = 50k

Ω

µF

R1 = 10k

Ω

Figure 46. Headphone Output Amplifier

INSTRUMENTATION AMPLIFIER

Because of their high speed, low offset voltages, and low noise

characteristics, the OP162/OP262/OP462 can be used in a wide

variety of high speed applications, including precision instru-

mentation amplifiers. Figure 47 shows an example of such an

application.

OP462-A

OP462-B

OP462-C

OP462-D

–VIN

+VIN

Ω

10k

Ω

1.9k

Ω

200

Ω

10 TURN

(OPTIONAL)

OUTPUT

Ω

10k

Ω

Figure 47. High Speed Instrumentation Amplifier

The differential gain of the circuit is determined by RG, where

DIFF

1 +

with the RG resistor value in kΩ. Removing RG sets the circuit

gain to unity.

The fourth op amp, OP462-D, is optional and is used to

improve CMRR by reducing any input capacitance to the

amplifier. By shielding the input signal leads and driving the

shield with the common-mode voltage, input capacitance is

eliminated at common-mode voltages. This voltage is derived

from the midpoint of the outputs of OP462-A and OP462-B by

using two 10 kΩ resistors followed by OP462-D as a unity-gain

buffer.

It is important to use 1% or better tolerance components for the

2 kΩ resistors, as the common-mode rejection is dependent on

their ratios being exact. A potentiometer should also be connected

in series with the OP462-C noninverting input resistor to ground

to optimize common-mode rejection.

The circuit in Figure 47 was implemented to test its settling

time. The instrumentation amp was powered with −5 V, so the

input step voltage went from −5 V to +4 V to keep the OP462

within its input range. Therefore, the 0.05% settling range is

when the output is within 4.5 mV. Figure 48 shows the positive

slope settling time to be 1.8 µs, and Figure 49 shows a settling

time of 3.9 µs for the negative slope.

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