REV. D

AD8601/AD8602/AD8604

–15–

For the high-side monitor, the monitor output voltage is

Monitor Output

R

R

R

I

SENSE

L

=× 







×

2

1

(3)

Using the components shown, the monitor output transfer func-

tion 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 that the A/D or D/A converters achieve their best perfor-

mance, 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 an 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

configuration, the low output impedance of the amplifier mini-

mizes 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 attenuation up to 500 kHz, which is the maximum Nyquist

frequency for the AD7476.

SCLK

C/ P

4

5

1

2

AD8601

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 frequen-

cies 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

2

AD8601

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 distor-

tion 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 cur-

rent 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

(AC'97)

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

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.