–16–

AD822

REV. A

MYLAR

1µF

1/2

AD822

L

R

HEADPHONES

32

Ω IMPEDANCE

4.99k

MYLAR

1µF

4.99k

1/2

AD822

10k

10k

47.5k

95.3k

47.5k

500µF

500µF

1

1

3

+3V

2

4

7

5

6

95.3k

8

0.1µF

0.1µF

CHANNEL 1

CHANNEL 2

Low Dropout Bipolar Bridge Driver

The AD822 can be used for driving a 350 ohm Wheatstone

bridge. Figure 47 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 A/D 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. Resistors R1 and

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

by:

G

=

49.4 k

Ω

R

G

+ 1

350

Ω

350

Ω

350

Ω

350

Ω

AD620

4

2

6

5

7

3

R2

20

Ω

–4.5V

10k

10k

10k

26.4k, 1%

R1

20

Ω

TO A/D CONVERTER

REFERENCE INPUT

AD589

49.9k

+1.235V

0.1µF

1µF

+5V

1µF

GND

1%

1%

1%

1/2

AD822

1

1

3

2

8

1/2

AD822

4

7

6

5

0.1µF

–5V

Figure 47. Low Dropout Bipolar Bridge Driver

Figure 46. 3 Volt Single Supply Stereo Headphone Driver

3 Volt, Single Supply Stereo Headphone Driver

The AD822 exhibits good current drive and THD+N perfor-

mance, 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 which consume more power and cannot run on

3 V power supplies.

In Figure 46, 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 head-

phones, which can be modeled as 32 ohm load resistors to

ground. This ensures that all signals in the audio frequency

range (20 Hz–20 kHz) are delivered to the headphones.

Cerdip (Q) Package

0.005 (0.13) MIN

0.055 (1.35) MAX

0.405 (10.29) MAX

0.150

(3.81)

MIN

0.200

(5.08)

MAX

0.070 (1.78)

0.030 (0.76)

0.200 (5.08)

0.125 (3.18)

0.023 (0.58)

0.014 (0.36)

0.100 (2.54)

BSC

SEATING

PLANE

0.060 (1.52)

0.015 (0.38)

4

1

5

8

0.310 (7.87)

0.220 (5.59)

0.320 (8.13)

0.290 (7.37)

0

°-15°

0.015 (0.38)

0.008 (0.20)

SOIC (R) Package

0.019 (0.48)

0.014 (0.36)

0.050

(1.27)

BSC

0.102 (2.59)

0.094 (2.39)

0.197 (5.01)

0.189 (4.80)

0.010 (0.25)

0.004 (0.10)

0.098 (0.2482)

0.075 (0.1905)

0.190 (4.82)

0.170 (4.32)

0.030 (0.76)

0.018 (0.46)

10

°

0

°

0.090

(2.29)

8

°

0

°

0.020 (0.051) x 45

°

CHAMF

1

8

5

4

PIN 1

0.157 (3.99)

0.150 (3.81)

0.244 (6.20)

0.228 (5.79)

0.150 (3.81)

Mini-DIP (N) Package

0.011

±0.003

(0.28

±0.08)

0.30 (7.62)

REF

15

°

0

°

PIN 1

4

5

8

1

0.25

(6.35)

0.31

(7.87)

0.10

(2.54)

BSC

SEATING

PLANE

0.035

±0.01

(0.89

±0.25)

0.18

±0.03

(4.57

±0.76)

0.033

(0.84)

NOM

0.018

±0.003

(0.46

±0.08)

0.125

(3.18)

MIN

0.165

±0.01

(4.19

±0.25)

0.39 (9.91) MAX

OUTLINE DIMENSIONS

Dimensions shown in inches and (mm).