Datasheet
AD824 Data Sheet
3 V, SINGLE SUPPLY STEREO HEADPHONE DRIVER
The AD824 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.
In Figure 35, each channel’s input signal is coupled via a 1 µF
Mylar capacitor. Resistor dividers set the dc voltage at the
noninverting inputs so that the output voltage is midway
between the power supplies (1.5 V). The gain is 1.5. Each half of
the AD824 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, which 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.
L
R
HEADPHONES
32Ω IMPEDANCE
3V
CHANNEL 1
CHANNEL 2
500µF
500µF
1µF
MYLAR
1µF
MYLAR
95.3kΩ
47.5kΩ
47.5kΩ
95.3kΩ
10kΩ
0.1µF 0.1µF
10kΩ
4.99kΩ
4.99kΩ
1/4
AD824
1/4
AD824
00875-035
Figure 35. 3 Volt Single Supply Stereo Headphone Driver
LOW DROPOUT BIPOLAR BRIDGE DRIVER
The AD824 can be used for driving a 350 Ω Wheatstone bridge.
Figure 36 shows one half of the AD824 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 front end. The other half of the
AD824 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 pro-
grammed using an external resistor R
G
and determined by:
1
k
4.
49
+
Ω
=
G
R
G
V
REF
–V
S
+V
S
R
G
–4.5V
R1
20Ω
350Ω
26.4kΩ, 1%
49.9kΩ
350Ω
R2
20Ω
350Ω
350Ω
TO ADC
REFERENCE INPUT
AD589
+1.235V
+5V
GND
+V
S
–V
S
–5V
–V
S
+V
S
7
6
5
4
3
2
1/4
AD824
1/4
AD824
AD824
10kΩ
1%
10kΩ
1%
0.1µF 1µF
0.1µF 1µF
10kΩ
1%
00875-036
Figure 36. Low Dropout Bipolar Bridge Driver
Rev. E | Page 14 of 16