AD8601/AD8602

–15–

REV. 0

Monitor Output

V

R

R

R

I

SENSE

L

=+ −







×

2

1

(3)

Using the components shown, the monitor output transfer function

is 2.5 V/A.

Using the AD8601 in Single Supply Mixed-Signal Applications

Single supply mixed-signal applications requiring 10 or more bits of

resolution demand both a minimum of distortion and a maximum

range of voltage swing to optimize performance. To ensure the A/D

or D/A converters achieve their best performance an amplifier often

must be used for buffering or signal conditioning. The 750

µV

maximum offset voltage of the AD8601 allows the amplifier to be

used in 12-bit applications powered from a 3 V single supply, and

its rail-to-rail input and output ensure no signal clipping.

Figure 6 shows the AD8601 used as a input buffer amplifier to

the AD7476, a 12-bit 1 MHz A/D converter. As with most A/D

converters, total harmonic distortion (THD) increases with higher

source impedances. By using the AD8601 in a buffer configura-

tion, the low output impedance of the amplifier minimizes THD

while the high input impedance and low bias current of the op

amp minimizes errors due to source impedance. The 8 MHz

gain-bandwidth product of the AD8601 ensures no signal attenu-

ation up to 500 kHz, which is the maximum Nyquist frequency

for the AD7476.

SCLK

C/ P

4

5

1

SDATA

CS

GND

AD7476/AD7477

SERIAL

INTERFACE

5V

SUPPLY

0.1 F

10 F

REF193

0.1 F

1 F

TANT

3V

680nF

Figure 6. A Complete 3 V 12-Bit 1 MHz A/D

Conversion System

Figure 7 demonstrates how the AD8601 can be used as an output

buffer for the DAC for driving heavy resistive loads. The AD5320

is a 12-bit D/A converter that can be used with clock frequencies

up to 30 MHz and signal frequencies up to 930 kHz. The rail-to-

rail output of the AD8601 allows it to swing within 100 mV of the

positive supply rail while sourcing 1 mA of current. The total

current drawn from the circuit is less than 1 mA, or 3 mW from

a 3 V single supply.

3

4

5

1

0V TO 3.0V

AD5320

2

1

3V

1 F

3-WIRE

SERIAL

INTERFACE

4

5

6

Figure 7. Using the AD8601 as a DAC Output Buffer to

Drive Heavy Loads

The AD8601, AD7476, and AD5320 are all available in space-

saving SOT-23 packages.

PC100 Compliance for Computer Audio Applications

Because of its low distortion and rail-to-rail input and output, the

AD860x is an excellent choice for low cost, single supply audio

applications, ranging from microphone amplification to line output

buffering. TPC 34 shows the total harmonic distortion plus noise

(THD + N) figures for the AD860x. In unity gain, the amplifier

has a typical THD + N of 0.004%, or –86 dB, even with a load

resistance of 600

Ω. This is compliant with the PC100 specification

requirements for audio in both portable and desktop computers.

Figure 8 shows how an AD8602 can be interfaced with an AC’97

codec to drive the line output. Here, the AD8602 is used as a

unity-gain buffer from the left and right outputs of the AC’97

CODEC. The 100

µF output coupling capacitors block dc current

and the 20

Ω series resistors protect the amplifier from short-circuits

at the jack.

U1-A

R2

2k

4

C1

100 F

+5V

1

8

2

3

+5V

AD1881

(AC97)

R4

20

5

6

7

R5

20

C2

100 F

NOTE: ADDITIONAL PINS

OMITTED FOR CLARITY

U1-B

U1 = AD8602D

R3

2k

28

35

36

Figure 8. A PC100 Compliant Line Output Amplifier

SPICE Model

The SPICE macro-model for the AD860x amplifier is available

and can be downloaded from the Analog Devices website at

http://www.analog.com. The model will accurately simulate a

number of both dc and ac parameters, including open-loop gain,

bandwidth, phase margin, input voltage range, output voltage

swing versus output current, slew rate, input voltage noise, CMRR,

PSRR, and supply current versus supply voltage. The model is

optimized for performance at 27

°C. Although it will function at

different temperatures, it may lose accuracy with respect to the

actual behavior of the AD860x.