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

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-

1

k

4

.

49

+

Ω

=

G

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

–5V

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%

Figure 36. Low Dropout Bipolar Bridge Driver

Rev. E | Page 14 of 16