AD822ARM-R2 datasheet(23/28 Pages) AD

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AD822

Rev. G | Page 23 of 28

3 V, SINGLE-SUPPLY STEREO HEADPHONE

DRIVER

The AD822 exhibits good current drive and THD + N

performance, even at 3 V single supplies. At 1 kHz, total

harmonic distortion plus noise (THD + N) equals –62 dB

(0.079%) for a 300 mV p-p output signal. This is comparable to

other single-supply op amps that consume more power and

cannot run on 3 V power supplies.

95.3kΩ

47.5kΩ

10kΩ

4.99kΩ

95.3kΩ

HEADPHONES

Ω IMPEDANCE

4.99kΩ

0.1µF

500µF

1µF

MYLAR

1µF

MYLAR

CHANNEL 1

CHANNEL 2

1/2

AD822

–

1/2

AD822

Figure 50. 3 V Single-Supply Stereo Headphone Driver

In Figure 50, each channel’s input signal is coupled via a 1 μF

Mylar capacitor. Resistor dividers set the dc voltage at the non-

inverting inputs so that the output voltage is midway between the

power supplies (1.5 V). The gain is 1.5. Each half of the AD822

can then be used to drive a headphone channel. A 5 Hz high-pass

filter is realized by the 500 μF capacitors and the headphones that

can be modeled as 32 Ω load resistors to ground. This ensures

that all signals in the audio frequency range (20 Hz to 20 kHz) are

delivered to the headphones.

LOW DROPOUT BIPOLAR BRIDGE DRIVER

The AD822 can be used for driving a 350 Ω Wheatstone bridge.

Figure 51 shows one-half of the AD822 being used to buffer the

AD589, a 1.235 V low power reference. The output of 4.5 V can

be used to drive an ADC converter front end. The other half of

the AD822 is configured as a unity gain inverter and generates

the other bridge input of −4.5 V. Resistor R1 and Resistor R2

provide a constant current for bridge excitation. The AD620 low

power instrumentation amplifier is used to condition the

differential output voltage of the bridge. The gain of the AD620 is

programmed using an external resistor RG and determined by

+1.235V

49.9kΩ

20Ω

25.4kΩ 1%

10kΩ 1%

350Ω

AD589

10kΩ 1%

20Ω

–4.5V

GND

+5V

–5V

1/2

AD822

–

1/2

AD822

+VS

–VS

VREF

+VS

–VS

AD820

–

0.1µF

1µF

TO A/D CONVERTER

REFERENCE INPUT

Figure 51. Low Dropout Bipolar Bridge Driver

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