Datasheet
–16–
AD822
REV. A
MYLAR
1µF
1/2
AD822
L
R
HEADPHONES
32Ω IMPEDANCE
4.99k
MYLAR
1µF
4.99k
1/2
AD822
10k
10k
47.5k
95.3k
47.5k
500µF
500µF
11
3
+3V
2
4
7
5
6
95.3k
8
0.1µF0.1µF
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
is programmed using an external resistor R
G
, and determined
by:
G =
49.4 kΩ
R
G
+1
350Ω
350Ω
350Ω
350Ω
V
REF
–V
S
+V
S
AD620
4
2
6
5
7
3
R
G
R2
20Ω
–4.5V
10k
10k
10k
26.4k, 1%
R1
20Ω
TO A/D CONVERTER
REFERENCE INPUT
AD589
49.9k
+1.235V
0.1µF
1µF
+5V
1µF
GND
1%
1%
1%
1/2
AD822
11
3
2
8
1/2
AD822
4
7
6
5
+V
S
+V
S
+V
S
–V
S
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.
C1821a–10–9/94
PRINTED IN U.S.A.
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)
41
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).