AD822
+3V
3
Low D r opout Bipolar Br idge D r iver
T he 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. T he output
of +4.5 V can be used to drive an A/D converter front end. T he
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. T he AD620
low power instrumentation amplifier is used to condition the
differential output voltage of the bridge. T he gain of the AD620
is programmed using an external resistor RG, and determined
by:
0.1µF
0.1µF
95.3k
47.5k
1µF
8
CHANNEL 1
1/2
AD822
1
MYLAR
500µF
2
L
4.99k
95.3k
10k
10k
HEADPHONES
32Ω IMPEDANCE
R
4.99k
7
49.4 kΩ
6
G =
+1
1/2
47.5k
1µF
AD822
RG
500µF
CHANNEL 2
5
4
MYLAR
+V
S
49.9k
Figure 46. 3 Volt Single Supply Stereo Headphone Driver
R1
20Ω
+1.235V
8
3
2
3 Volt, Single Supply Ster eo H eadphone D r iver
T he AD822 exhibits good current drive and T HD+N perfor-
mance, even at 3 V single supplies. At 1 kHz, total harmonic
distortion plus noise (T HD+N) equals –62 dB (0.079%) for a
300 mV p-p output signal. T his is comparable to other single
supply op amps which consume more power and cannot run on
3 V power supplies.
1/2
AD822
TO A/D CONVERTER
REFERENCE INPUT
1
AD589
26.4k, 1%
350Ω
10k
1%
+V
S
350Ω
7
3
2
AD620
R
6
G
350Ω
350Ω
5
4
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). T he 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. T his ensures that all signals in the audio frequency
range (20 Hz–20 kHz) are delivered to the headphones.
10k
1%
V
REF
–V
S
10k
1%
6
5
1/2
AD822
+V
S
+5V
–5V
–4.5V
7
1µF
1µF
0.1µF
4
R2
20Ω
GND
0.1µF
+V
S
–V
S
Figure 47. Low Dropout Bipolar Bridge Driver
O UTLINE D IMENSIO NS
D imensions shown in inches and (mm).
Mini-D IP (N) P ackage
Cer dip (Q ) P ackage
SO IC (R) P ackage
0.005 (0.13) MIN
0.055 (1.35) MAX
0.150 (3.81)
8
5
0.25
(6.35)
8
5
0.31
8
1
5
4
PIN 1
0.310 (7.87)
0.244 (6.20)
0.228 (5.79)
(7.87)
0.157 (3.99)
0.150 (3.81)
0.220 (5.59)
1
4
1
4
PIN 1
0.070 (1.78)
0.030 (0.76)
0.39 (9.91) MAX
0.035±0.01
(0.89±0.25)
0.405 (10.29) MAX
0.165±0.01
(4.19±0.25)
0.200
0.060 (1.52)
0.015 (0.38)
0.197 (5.01)
0.189 (4.80)
(5.08)
MAX
0.18±0.03
(4.57±0.76)
0.125
(3.18)
MIN
0.102 (2.59)
0.094 (2.39)
0.150
(3.81)
MIN
0.010 (0.25)
0.004 (0.10)
0.200 (5.08)
0.125 (3.18)
0.10
(2.54)
0.018±0.003
(0.46±0.08)
0.033
(0.84)
NOM
0.019 (0.48)
0.014 (0.36)
0.050
(1.27)
BSC
SEATING
PLANE
SEATING
PLANE
0.023 (0.58)
0.014 (0.36)
0.100 (2.54)
BSC
BSC
0.30 (7.62)
REF
0.320 (8.13)
0.020 (0.051) x 45
CHAMF
°
0.290 (7.37)
0.190 (4.82)
0.170 (4.32)
8
0
°
°
0.090
(2.29)
0.011±0.003
(0.28±0.08)
10
°
0.015 (0.38)
0.008 (0.20)
0°
0.030 (0.76)
0.018 (0.46)
0.098 (0.2482)
0.075 (0.1905)
15
°
0
°
0°-15°
REV. A
–16–
ADI [ ADI ]
